Uptake Of O2 Research Articles

Rates of carbonate dissolution in permeable sediments estimated from pore‐water profiles: The role of sea grasses

In this study we estimate sediment carbonate dissolution rates for sandy sea grass sediments on the Bahamas Bank using an inverse pore‐water advection/diffusion/reaction model constrained by field observations. This model accounts for sea grass O2 input to these sediments, and also parameterizes pore‐water advection through these permeable sediments as a nonlocal exchange process. The resulting rates of carbonate dissolution are positively correlated with sea grass density, and are comparable with previous rate estimates for Florida Bay sediments. In contrast, the advective uptake of O2 by these sediments decreased with increasing sea grass density. This suggests that the competing interplay between bottom‐water flow, near‐seabed pressure gradients, and the presence of a sea grass canopy is important in controlling this type of sediment oxygen uptake. When the carbonate dissolution rates estimated here are examined in the context of carbonate budgets for shallow‐water carbonate platforms systems, they suggest that carbonate dissolution may be a significant loss term in these budgets. Sea grass‐mediated carbonate dissolution may also exert a negative feedback on rising atmospheric CO2, although the magnitude of this effect remains to be quantified.

Papel del túbulo en la vasoconstricción renal inducida por ciclosporina

Introduction:Cyclosporine (CyA) has proved to induce cell apoptosis on cultured proximal tubule cells. However, there is no much data about the in vivo functional consequences of this injury or the long time observed CyA-induced renal vasoconstriction. Material and Methods:In a swine model of subacute CyA nephrotoxicity (10 mg/ Kg. d x 15 days), we performed a right nephrectomy, followed by left renal artery, vein and ureter catheterisation. After inducing water diuresis, three clearance periods of 15 minutes were performed before and after a furosemide 1 mg/kg infusion. Plasma and urine electrolytes, blood gas, acid excretion, plasma renin activity and aldosterone concentration, GFR, RPF, RBF, intra-renal vascular resistances, glomerular filtration pressure, distal Cl- delivery, water clearance and TTKG were measured or estimated on 7 control and 7 treated animals. Right kidney was processed for NaKATPase activity and immunostaining. Results:Treated animals presented detaching proximal cells, luminal blebbing and loss of tight junctions. Cortical but not medullar sodium pump was internalised and partially inactive. Treated animals showed much lower fractional excretions of Na+, with significantly higher distal fractional reabsorption of Cl-. Distal shift in fluid load resulted in a significant rise in renal O2 consumption, and modifications in the global renal estequiometry of Na+ transport/O2 uptake. Several consequences followed this situation: preglomerular resistances increased 3 times with only minor changes in postglomerular resistances and renal blood and plasma flow were significantly reduced. Furosemide partially reversed these effects. A slight increase in fractional filtration prevented GFR differences to become statistically significant. Conclusión:subacute CyA treatment even al doses not modifying GFR, may cause proximal tubule Na+ transport impairment, resulting in increased rates of distal delivery and absorption of fluid load. Renal uptake of O2 may be increased and tubule glomerular feedback should be expected to be activated. Absence of changes of GFR with furosemide is an early sign of CyA renal damage.

Role of wind stress and heat fluxes in interannual‐to‐decadal variability of air‐sea CO2 and O2 fluxes in the North Atlantic

A coupled ecosystem‐circulation model of the North Atlantic is used to examine the individual contributions by wind stress and surface heat fluxes to naturally driven interannual‐to‐decadal variability of air‐sea fluxes of CO2 and O2 during 1948–2002. The model results indicate that variations in O2 fluxes are mainly driven by variations in surface heat fluxes in the extratropics (15°N to 70°N), and by wind stress in the tropics (10°S to 15°N). Conversely, variations in simulated CO2 fluxes are predominantly wind‐stress driven over the entire model domain (18°S to 70°N); while variability in piston velocity and surface heat fluxes is less important. The simulated uptake of O2 by the North Atlantic amounts to 70 ± 11 Tmol yr−1 to which the subpolar region (45°N to 70°N) contributes by 62 ± 10 Tmol yr−1. Whereas the subpolar North Atlantic takes up more than 2/3 of the total carbon absorbed by the North Atlantic in our model (about 0.3 Pg C yr−1), interannual variability of air‐sea CO2 fluxes reaches similar values (about 0.01 Pg C yr−1 each) in the subpolar (45°N to 70°N), the subtropical (15°N to 45°N) and the equatorial (10°S to 15°N) Atlantic.

Superoxide production and oxygen consumption in endothelium-intact and -denuded artery stimulated by angiotensin II

Arteries stimulated by angiotensin II (AII) to contract do not display the expected augmentation of O2 consumption seen with other cardiovascular contractile agonists. We tested the hypothesis that superoxide (O2-) or other reactive oxidant species generated by AII played a role in the paradoxical O2 consumption response in porcine carotid artery, with or without an intact endothelium. Endothelium-denuded arteries were incubated with either 1 microM diphenylene iodonium (DPI), an inhibitor of NAD(P)H oxidase, 300 u/ml superoxide dismutase (SOD), a scavenger of O2-, or 20 U/ml catalase, an enzyme which promotes conversion of O2- (scavenged in the form of H2O2) to O2. DPI treatment resulted in the expected increase in O2 consumption upon contractile activation with AII challenge (1.05+/- 0.23 micromol/g/min; n = 6, p < .01), as did treatment with SOD (0.67+/- 0.20 micromol/g/min; n = 4, p < .05). Catalase incubation resulted in a burst of O2 generation upon AII challenge (1.30 +/- 0.21 micromol/g/min; n = 10, p < .001). In endothelium-intact arteries, O2 consumption was again not augmented with AII challenge; instead, a burst of O2 production was observed (0.66 +/- 0.22 micromol/g/min; n = 9, p < .05), which was not affected further by addition of catalase. Thus, the absence of apparent augmentation of O2 consumption during contractile activation of endothelium-denuded arteries was attributed to simultaneous NAD(P)H oxidase-dependent production of O2-, and attendant H2O2 and O2 generation which either and masked the detection of O2 consumed or suppressed mitochondrial uptake of O2, or both. An intact endothelium was required to manifest the burst of O2 generation with AII stimulation under normal conditions.

Kinetic analyses of the OJIP chlorophyll fluorescence rise in thylakoid membranes.

N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was previously used to study the kinetics of the OJIP chlorophyll fluorescence rise. The present study is an attempt to elucidate the origin of TMPD-induced delay and quenching of the I-P step of fluorescence rise. For this purpose, we analyzed the kinetics of OJIP rise in thylakoid membranes in which electron transport was modified using ascorbate, methyl viologen (MV), and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB). In the absence of TMPD, the OJIP kinetics of fluorescence induction (FI) was not altered by ascorbate. However, ascorbate eliminated the I-P rise delay caused by high concentrations of TMPD. On the other hand, neither ascorbate nor DBMIB, which blocks the electron release from Photosystem II (PS II) at the cytochrome b6/f complex, could prevent the quenching of I-P rise by TMPD. In control thylakoids, MV suppressed the I-P rise of FI by about 60. This latter effect was completely removed if the electron donation to MV was blocked by DBMIB unless TMPD was present. When TMPD intercepted the linear electron flow from PS II, re-oxidation of TMPD by photosystem I (PS I) and reduction of MV fully abolished the I-P rise. The above is in agreement with the fact that TMPD can act as an electron acceptor for PS II. With MV, the active light-driven uptake of O2 during re-oxidation of TMPD by PS I contributes towards an early decline in the I-P step of the OJIP fluorescence rise.

Nitrate Regeneration Coupled to Degradation of Different Size Fractions of DON by the Picoplankton in the Elbe Estuary.

Bacterial conversion of high (HMW > 3,000 Da) and low (LMW < 3,000 Da) molecular weight DON (dissolved organic nitrogen) was studied along the freshwater section of the Elbe estuary during the summer of 1997. Indigenous populations of picoplankton were incubated in a flow-through chamber that allowed a constant exchange of sterile, filtered Elbe water as the culture medium for the microorganisms, which remained within the chamber. Nitrogen conversion was followed by changes in the concentrations of total and low molecular weight DON and dissolved inorganic nitrogen compounds, the uptake of O2, and bacterial growth. Along the Elbe estuary, total DON concentrations varied between 0.69 and 1.1 mg N L-1, of which between 64 and 79% was LMW-DON. Ammonium was a minor nutrient present in the Elbe at concentrations below 0.26 mg N L-1. During incubation in the laboratory between 27 and 64% of the LMW-DON was consumed at rates ranging from 24 to 51 µg N L-1 h-1. HMW-DON was used only when the degradable LMW-DON pool became exhausted and accounted for between 60 and 100% of the HMW-DON. This produced an increase in the DON consumption rate between 43 and 79 µg N L-1 h-1. Nitrification rates were independent of the external ammonium concentration until it decreased to below 1 µg N-NH4 L-1. Most of the N in the nitrification process originated as NH4 regenerated from DON. Between 75 and 100% of the LMW-DON and ammonium consumed was rapidly converted to nitrate. This amount decreased to between 65 and 85% when HMW-DON was consumed in addition to the LMW-DON. DON and ammonium consumption supported nitrification rates up to 71 µg N L-1 h-1. The amount of DOC (dissolved organic carbon) degraded was not equivalent to the C:N ratio of the total dissolved organic matter. Calculations based on oxygen consumption for respiration and ammonium regeneration revealed that the substrates used during the incubations contained C:N at ratios of about 3:1. These results suggest that the nitrogen-rich compounds had been removed from the dissolved organic matter and subsequently consumed by bacteria, while the carbon skeleton remained mostly unaffected by the degradation processes.

Cardio-respiratory effects of chloramine-T exposure in rainbow trout

In order to establish whether the blood gas respiratory disturbances noted with exposure to chloramine-T are due to differences in the rates of uptake of O2 and excretion of CO2 or gill blood flow, adult rainbow trout (Oncorhynchus mykiss) were fitted with dorsal aorta and bulbus arteriosus catheters to facilitate blood pressure recordings, an ultrasonic blood flow probe and opercular impedance electrodes. Fish received either a 45-min static exposure to 9 mg l−1 chloramine-T or tap water (control) and continuous recordings of blood pressure, and ventilation frequency and amplitude were made. Pre- and post-exposure arterial and venous blood samples were taken and analyzed for O2 and CO2 content, hemoglobin concentration and hematocrit. Chloramine-T exposure had no effect on any of the continuously recorded parameters. However, individual measurements (made immediately prior to and following exposure) of cardiac output and O2 uptake rates increased significantly following exposure to chloramine-T compared to before exposure. CO2 excretion rates were unaffected by chloramine-T exposure. Calculation of the perfusion convection requirement showed a significant increase for CO2 but not for O2. It was concluded that increases in O2 uptake resulted from increased cardiac output but that CO2 excretion, a diffusion-limited process, was not increased due to additional diffusive limitations caused by the irritant effect of chloramine-T.

Effect of chronic sodium cyanate administration on O2 transport and uptake in hypoxic and normoxic exercise.

Systemic O2 transport during maximal exercise at different inspired PO2 (PIO2) values was studied in sodium cyanate-treated (CY) and nontreated (NT) rats. CY rats exhibited increased O2 affinity of Hb (exercise O2 half-saturation pressure of Hb = 27.5 vs. 42.5 Torr), elevated blood Hb concentration, pulmonary hypertension, blunted hypoxic pulmonary vasoconstriction, and normal ventilatory response to exercise. Maximal rate of convective O2 transport was higher and tissue O2 extraction was lower in CY than in NT rats. The relative magnitude of these opposing changes, which determined the net effect of cyanate on maximal O2 uptake (VO2 max), varied at different PIO2: VO2 max (ml. min-1. kg-1) was lower in normoxia (72.8 +/- 1.9 vs. 81. 1 +/- 1.2), the same at 70 Torr PIO2 (55.4 +/- 1.4 vs. 54.1 +/- 1.4), and higher at 55 Torr PIO2 (48 +/- 0.7 vs. 40.4 +/- 1.9) in CY than in NT rats. The beneficial effect of cyanate on VO2 max at 55 Torr PIO2 disappeared when Hb concentration was lowered to normal. It is concluded that the effect of cyanate on VO2 max depends on the relative changes in blood O2 convection and tissue O2 extraction, which vary at different PIO2. Although uptake of O2 by the blood in the lungs is enhanced by cyanate, its release at the tissues is limited, probably because of a reduction in the capillary-to-tissue PO2 diffusion gradient secondary to the increased O2 affinity of Hb.

Oxidation activity of cerium supported NaZSM-5 zeolites with and without added alkali metals in the gas-phase catalytic oxidation of benzyl alcohol

The gas-phase catalytic oxidation of benzyl alcohol was carried out over low [CeL, ∽1×10-2 mmol (g-NaZSM-5)-1] and high [CeH, ∽1–2 mmol (g-NaZSM-5)-1] Ce supported NaZSM-5 zeolites and alkali metal added counterparts. The Ce was supported on NaZSM-5 zeolites by both ion-exchange (CeL-NaZSM-5) and impregnation (CeL- and CeH/NaZSM-5) methods. The alkali metal added to the low and high Ce supported NaZSM-5 catalysts was found to be quite different in influence on the catalytic activity of benzyl alcohol oxidation. The addition of alkali metal to the CeL- and/or CeL/NaZSM-5 zeolites was found to promote selectively catalytic activity for the partial oxidation of benzyl alcohol. The addition of the alkali metal caused an increase in the amount of O2 uptake of the prereduced CeL- and/or CeL/NaZSM-5 catalysts. A correlation was observed between the amount of O2 uptake and the amount of alkali metal added to the CeL- and/or CeL/NaZSM-5 catalysts. The alkali metal added to the CeL- and/or CeL/NaZSM-5 catalysts was suggested to promote the mobility of the oxygen species in the low Ce supported catalysts, whose oxygen species are considered to play an important role in benzaldehyde formation. The alkali metal added to the CeH/NaZSM-5 catalysts inversely tended to decrease the oxidation activity. The addition of the alkali metal to the CeH/NaZSM-5 catalyst made the particle size of CeO2 formed in the CeH/NaZSM-5 larger, and the redox ability of the oxidic cerium lower through the inhibition of the uptake of O2.

Strategies for migration in the terrestrial christmas island red crab gecarcoidea natalis: intermittent versus continuous locomotion

The terrestrial red crab Gecarcoidea natalis undertakes an annual breeding migration and must sustain locomotion for prolonged periods. The migrating crabs must travel a specific distance in a fixed time and can either walk at a constant speed or walk faster for short periods and then pause to feed or rest. To simulate the potential differences between continuous and intermittent locomotion during the migration, red crabs were sampled after walking at a voluntary speed for 5 or 20 min without pausing or after 20 min of enforced walking intermittently at approximately twice that speed. The respiratory and metabolic status of the crabs was investigated during the different exercise regimes to assess which strategy might be more advantageous during the migration. The gills and lungs appeared to function similarly in gas exchange, and the PO2 in the haemolymph was 8.2 kPa which fully saturated the haemocyanin with O2. The uptake of O2 by red crabs was diffusion-limited and the diffusion coefficient (Ldiff) varied from 0.53 in resting crabs to 0. 8 post-exercise. Post-exercise, red crabs experienced a mixed respiratory/metabolic acidosis which was greatest (0.2 pH units) in crabs walking intermittently, i.e. at a higher speed. Haemolymph l-lactate concentrations peaked at 5 mmol l-1 immediately post-exercise in the intermittent exercise group, whereas after 20 min of continuous exercise haemolymph l-lactate continued to increase, reaching a maximum of 2.5 mmol l-1 at 1 h post-exercise. l-Lactate recovered slowly to basal levels within 5 h. The maximum rate of l-lactate clearance from the haemolymph was only 1.75 mmol l-1 h-1, and short pauses in exercise were insufficient for substantial l-lactate reoxidation. Exercise regimes in the laboratory were within the locomotor speeds determined for migrating red crabs, which overall have a mean walking speed close to their aerobic limit but periodically pause and also exceed this limit by three- to fourfold.

Modified Atmosphere Packaged Cut Iceberg Lettuce: Effect of Temperature and O2Partial Pressure on Respiration and Quality

The effect of oxygen and carbon dioxide partial pressure (pO2 and pCO2, respectively) and temperature on respiratory patterns and quality of cut iceberg lettuce was examined in modified atmosphere (MA) packages. The changes in headspace pO2 of packaged lettuce with time were related to void volume, storage temperature, mass, and decreasing respiration rate. Uptake of O2 was modeled using a Michaelis−Menten-type equation. At 5 and 10 °C, maximum O2 uptakes were 143 and 213 pmol·g-1·s-1 and the pO2 at half-maximal (k1/2) values were 0.26 and 0.19 kPa, respectively. On the basis of ethanol appearance in the headspace, the fermentation induction point was 0.3−0.4 kPa of O2 at 5 °C and 0.6−0.8 kPa of O2 at 10 °C. Acetaldehyde and ethyl acetate were detected at <0.4 kPa of O2 at 5, 10, and 20 °C (1 kPa ∼ 1% at STP). The extent of browning increased with headspace pO2 but was not related to headspace pCO2. Keywords: Modified atmosphere packaging; cut iceberg lettuce; color; respiratory patterns; volatile production

Effect of high CO2 level on the titres of -aminobutyric acid, total polyamines and some pathogenesis-related proteins in cherimoya fruit stored at low temperature

In this study the effect of treatment with 20% CO2 plus 20% O2 for 3 d on γ-aminobutyric acid (GABA) was analysed and total polyamine titres and the production of some pathogenesis-related proteins (PR-proteins) in cherimoya (Annona cherimola Mill.) fruit stored at low temperature. In immunoassays with anti-PR-Q and PR-2 protein sera, high CO2 levels were found to provoke the co-ordinated accumulation of a chitinase-like protein and 1,3-β-glucanase. Chitinase activity was higher in treated than in untreated fruit. At the end of CO2 treatment, total polyamine and γ-aminobutyric acid content and uptake of O2 were observed to be higher in treated compared to untreated fruit, but the accumulation of these compounds decreased when the fruit was transferred to air. Since this treatment effectively retains the fruit quality (Escribano et al., 1997), high CO2 levels may have a direct effect on the activation of the above-mentioned specific responses that enables cherimoya fruit to overcome chilling temperature. The relationship between the activation of the defence system and the capacity to regulate cytoplasmic pH in CO2-treated fruits was also addressed.

Intraphagosomal chlorination dynamics and yields determined using unique fluorescent bacterial mimics.

Fluorescein was covalently attached through a cystamine linker group to carboxy-derivatized polyacrylamide microspheres to generate phagocytosable particles containing fluorescent reporter groups. A unique feature of these beads is that the dye was recoverable in near-quantitative yield from intracellular environments by thiol reduction of the cystamine disulfide bond. Fluorescence microscopy indicated that individual neutrophils could bind as many as approximately 20 serum-opsonized beads, although no appreciable cellular association was observed for unopsonized beads. By using methyl viologen to quench external fluorescence, it was demonstrated that 70-90% of the neutrophil-associated fluorescein on opsonized beads was inaccessible to the medium. The particle-bound fluorescein underwent near-stoichiometric conversion to chlorinated derivatives when reacted with HOCl or the cell-free myeloperoxidase (MPO)-H2O2-Cl- system; products were identified by HPLC separation and electrospray ionization mass spectrometry of the recovered dye. Fluorescence changes accompanying phagocytosis were consistent with chlorination of the dye; fluorescence spectrometric and chemical trapping measurements indicated that intraphagosomal chlorination was far more extensive than extracellular chlorination. Yields of recovered chlorofluoresceins determined by HPLC indicated that sufficient HOCl had been produced intracellularly to kill entrapped bacteria. Fluorescein chlorination coincided approximately with phagocytosis and stimulated uptake of O2 by the cells. Demonstration that HOCl is produced within phagosomes in sufficient concentrations to kill bacteria on a time scale associated with death constitutes strong evidence in support of a primary role for HOCl in the microbicidal action of neutrophils.

Oxygen uptake and carbon dioxide excretion by the branchial and postbranchial regions of adults of the lampreyGeotria australis in air

O2 uptake and CO2 excretion by the branchial and postbranchial regions of adults of the lamprey Geotria australis have been measured in humidified air at 15 and 5°C. At 15°C, the mean standard V˙O2for whole animals was 31.9 μl·gm–1·hr–1, which is similar to the interpolated V˙O2in water at the same temperature and time of year. The corresponding mean standard V˙CO2was 25.2 μl·gm–1·hr–1, producing an RQ of 0.79. The branchial region was responsible for ˜87% of O2 uptake and ˜80% of CO2 excretion, which indicates that the gills of lampreys retain their integrity in air and thereby facilitate gas exchange. The continuous pumping of the branchial chamber would also facilitate gas exchange across the gills. The RQ is far higher in the postbranchial than branchial region, i.e., 1.26 vs. 0.72. The proportionately greater excretion of CO2 than uptake of O2 by the postbranchial than branchial region is presumably related to a combination of the greater capacitance of tissue for CO2 than O2 and the presence of a thicker tissue barrier in the skin of the trunk and tail than in the lamellae of the gills. At 5°C, the mean standardV˙O2andV˙CO2for whole animals declined markedly to 13.1 and 13.5 μl·gm–1·hr–1, respectively. The corresponding rise in RQ from 0.79 at 15°C to 1.03 at 5°C implies that aerobic metabolism now utilizes solely carbohydrate, rather than lipid and some carbohydrate. The transfer to solely carbohydrate metabolism at 5°C may be triggered by a need to supplement aerobic metabolism with anaerobic metabolism to compensate for an apparent shortfall in oxygen uptake produced by inadequate ventilation of the gills. J. Exp. Zool. 278:290–298, 1997. © 1997 Wiley-Liss, Inc.

Glucose, lactate and oxygen metabolism in the fetal pig during late gestation.

Using [U-14C]glucose tracer, rates of umbilical uptake, utilization and production of glucose, and of CO2 production from glucose carbon, were measured in seven chronically catheterized fetal pigs, when the sow was in the fed state, between 100 and 113 days of gestation (term, 114 +/- 2 days). At the same time, rates of umbilical O2 and lactate uptake were determined in all seven fetuses by the Fick principle. The mean fetal rates of umbilical glucose uptake, glucose utilization and CO2 production from glucose carbon were 38.4 +/- 4.2, 41.3 +/- 5.2 and 126.9 +/- 12.6 mumol min-1 (kg fetal body weight)-1, respectively (n = 7), No glucose production was therefore detected in the fetuses. Production of CO2 from glucose carbon accounted for 37.3 +/- 3.4% (n = 7) of the umbilical O2 uptake, which averaged 340 +/- 13 mumol min-1 kg-1 (n = 7). There was also significant umbilical lactate uptake in the fetal piglets when the sow was in the fed state (32.6 +/- 10.4 mumol min-1 kg-1, n = 7, P < 0.05). No significant changes in fetal glucose, O2 or lactate metabolism were observed with increasing age towards term. The fetal rates of glucose metabolism and of umbilical uptake of O2 and lactate were not correlated with fetal blood glucose level. Hence, glucose is used for both oxidative and non-oxidative metabolism in utero and is an important, although not the sole, source of carbon for metabolic processes in the fetal pig during late gestation.

Uptake and Release of O2 by Myohemerythrin. Evidence for Different Rate-Determining Steps and a Caveat

The oxy adducts of hemoglobins and hemerythrins are photosensitive, enabling the study of O{sub 2} recombination with deoxy forms produced by laser flash photolysis. Results to date have been interpreted in terms of consecutive O{sub 2} recombination equilibria for members of both protein families, indicating that O{sub 2} passage through these protein matrices involves multiple barriers. In relating rate and equilibrium data at physiological temperatures for these proteins, it has been tacitly assumed by many workers that K{sub eq}=k{sub on}/k{sub off}. In this communication, we report results for Themiste zostericola myohemerythrin (Mhr) and demonstrate that this assumption is not valid. Mhr binds dioxygen by reducing it to hydroperoxide; concomitantly, diferrous deoxyMhr is oxidized to the diferric oxy form. The (hydro)peroxo {yields} Fe{sup III} charge-transfer transition, centered at 500 nm, of oxyMhr was used to monitor the kinetics of O{sub 2} uptake and release. Rapid mixings of oxyMhr with sodium dithionite was used to scavenge O{sub 2} in solution, initiating O{sub 2} release from the protein. Rate constants for this reaction as a function of temperature and pressure are plotted and summarized. These results point to a rate-determining step that occurs prior to Fe-O bond formation. 14 refs., 3 figs., 1more » tab.« less

Causes and location of non‐specific effects of SHAM on O2 uptake by wheat roots

Uptake of O2 by whole, detached, root systems of wheat (Triticum aestivum L. cv. Alexandria) was titrated with salicylhydroxamic acid (SHAM) in the presence and absence of cyanide. The resulting Qall plot was non‐linear indicating that SHAM was acting non‐specifically. The nature of the non‐specific effects was investigated in reverse titration experiments. Uptake of O2 was titrated with KCN in the presence and absence of SHAM at 1 mM and 25 mM, which yielded Qcy1 values of &lt; 1 and &gt; 1, respectively. The results suggest that at 25 mM, SHAM inhibits the cytochrome pathway, but at 1 mM it stimulates an O2‐consuming process which is likely to be a peroxidase. A SHAM‐stimulated peroxidase could easily be washed from these roots. In vitro, the peroxidase was stimulated to a similar extent by low (1 mM) and high (25 mM) concentrations of SHAM. Failure to inhibit with high concentrations of SHAM distinguishes this peroxidase from those bitherto eluted from root tissue. Reverse titration experiments in the presence and absence of 1 mM SHAM indicated that there were no significant side effects of SHAM in root tips. These data are supported by the negligible peroxidase activity that was washed from this root fraction. In contrast, significant side effects occurred in vivo, and substantial peroxidase activity was measured in vitro, from sections 4–6 cm and 18–20 cm behind the seminal root apex. The greatest activity was found with the 4–6 cm section which may be associated with high rates of cell wall lignification. The implications of these results for measurements of root respiration are discussed.

Oxygen, glucose, and lactate uptake by fetus and placenta during prolonged hypoxemia

Our aim was to compare the effects of short (4 h) and prolonged (24 h) periods of reduced uterine blood flow (RUBF) on fetal and placental uptake of O2, glucose, and lactate. In pregnant sheep, uterine and umbilical blood flows were measured under normal conditions and after 4 and 24 h of RUBF. A 50% reduction in uterine blood flow caused a 56% reduction in fetal arterial O2 saturation (SaO2). Umbilical blood flow increased from 325 +/- 33 to 378 +/- 32 ml.min-1.kg-1 (P < 0.05) after 4 h but was not different from pre-RUBF values after 24 h. O2 uptake by the gravid uterus was not altered by RUBF, due to an increase (84%) in uterine O2 extraction. Similarly, uteroplacental and fetal O2 consumptions and fetal glucose uptake were not affected by RUBF, whereas uteroplacental glucose uptake was significantly reduced after 4 h (by 42%) and 24 h (by 58%) of RUBF. Fetal lactate uptake was greatly reduced from 78.7 +/- 15.5 to -167 +/- 57 mumol.min-1.kg-1 after 4 h and to -198 +/- 80 mumol.min-1.kg-1 after 24 h of RUBF; negative values indicate placental lactate uptake from the fetal circulation. Thus, although RUBF significantly reduced fetal SaO2, fetal and uteroplacental O2 consumptions did not change. In addition, although fetal glucose uptake was not altered by RUBF, during RUBF the placenta became a major site of lactate clearance from the fetal circulation.

Association of glycerylphosphorylcholine with human sperm and effect of capacitation on their metabolism.

The presence and localization of glycerylphosphorylcholine (GPC) on the surface of human sperm, as well as the metabolism of its breakdown product L-glycerol 3 phosphate (G3P), were investigated. GPC was found to be associated with sperm after penetrating cervical mucus and was present after repeated washing of the sperm. GPC was partially released by treatment with 0.4 M NaCl in 0.01 M sodium phosphate buffer (pH 7.4) and localized to the head region after sperm fractionation. G3P did not increase O2 uptake of uncapacitated human sperm. However, under aerobic conditions, lactate accumulated when exogenous G3P or uterine GPC diesterase was added to sperm in suspension. The uptake of O2 by washed capacitated sperm pre-incubated with 1 unit of rat uterine GPC diesterase for 30 min was significant. This effect was inhibited by 2 microM oligomycin indicating that oxidative phosphorylation had occurred. The present study indicates that GPC may play a role in the metabolism of human sperm after capacitation.

Electron transport and photophosphorylation by Photosystem I in vivo in plants and cyanobacteria

Recently, a number of techniques, some of them relatively new and many often used in combination, have given a clearer picture of the dynamic role of electron transport in Photosystem I of photosynthesis and of coupled cyclic photophosphorylation. For example, the photoacoustic technique has detected cyclic electron transport in vivo in all the major algal groups and in leaves of higher plants. Spectroscopic measurements of the Photosystem I reaction center and of the changes in light scattering associated with thylakoid membrane energization also indicate that cyclic photophosphorylation occurs in living plants and cyanobacteria, particularly under stressful conditions.In cyanobacteria, the path of cyclic electron transport has recently been proposed to include an NAD(P)H dehydrogenase, a complex that may also participate in respiratory electron transport. Photosynthesis and respiration may share common electron carriers in eukaryotes also. Chlororespiration, the uptake of O2 in the dark by chloroplasts, is inhibited by excitation of Photosystem I, which diverts electrons away from the chlororespiratory chain into the photosynthetic electron transport chain. Chlororespiration in N-starved Chlamydomonas increases ten fold over that of the control, perhaps because carbohydrates and NAD(P)H are oxidized and ATP produced by this process.The regulation of energy distribution to the photosystems and of cyclic and non-cyclic phosphorylation via state 1 to state 2 transitions may involve the cytochrome b 6-f complex. An increased demand for ATP lowers the transthylakoid pH gradient, activates the b 6-f complex, stimulates phosphorylation of the light-harvesting chlorophyll-protein complex of Photosystem II and decreases energy input to Photosystem II upon induction of state 2. The resulting increase in the absorption by Photosystem I favors cyclic electron flow and ATP production over linear electron flow to NADP and 'poises' the system by slowing down the flow of electrons originating in Photosystem II.Cyclic electron transport may function to prevent photoinhibition to the photosynthetic apparatus as well as to provide ATP. Thus, under high light intensities where CO2 can limit photosynthesis, especially when stomates are closed as a result of water stress, the proton gradient established by coupled cyclic electron transport can prevent over-reduction of the electron transport system by increasing thermal de-excitation in Photosystem II (Weis and Berry 1987). Increased cyclic photophosphorylation may also serve to drive ion uptake in nutrient-deprived cells or ion export in salt-stressed cells.There is evidence in some plants for a specialization of Photosystem I. For example, in the red alga Porphyra about one third of the total Photosystem I units are engaged in linear electron transfer from Photosystem II and the remaining two thirds of the Photosystem I units are specialized for cyclic electron flow. Other organisms show evidence of similar specialization.Improved understanding of the biological role of cyclic photophosphorylation will depend on experiments made on living cells and measurements of cyclic photophosphorylation in vivo.