Nmol O2 Min-1 Research Articles

Oxygen Consumption and Luminescence of Maurolicus Photophores Stimulated by Potassium Cyanide

ABSTRACT Isolated photophores of Maurolicus muelleri, maintained in saline at 20 °C, consume oxygen at a mean rate of 1·25 ± 0·07 nmol O2 min-1(N = 50). In the presence of 5 × 10−6 mol l−1 KCN, seven preparations did not luminesce while two showed only dim luminescence. In all nine preparations, the resting oxygen consumption decreased by about 50%. In the presence of 5× 10−s mol l−1 KCN, all of the photophores produced a slow, low luminescence and their oxygen consumption decreased by about 75%. In the presence of 5× 10−4mol l−1 KCN, all of the photophores produced a slow, high luminescence and their oxygen consumption decreased rapidly by about 92%. It is suggested that the oxygen needs for light production by the isolated photophores of the mesopelagic fish, Maurolicus, differ from those of the epipelagic fish, Porichthys.

Oxygen consumption and active sodium and chloride transport in bovine tracheal epithelium.

The O2 consumption (Jr) and the short-circuit current (Ji) were measured simultaneously in bovine tracheal epithelium in vitro. In this tissue, Ji is the sum of two active transport processes, Cl- secretion and Na+ absorption. Jr was determined from the decrease of PO2 in the incubation solution, at 37 +/- 0.05 degrees C and at a PO2 around 600 torr. Microbial contamination and leaks of dissolved O2 from the solution never exceeded 4% of the rate of PO2 decrease due to the O2 consumption of the tissue. Ji and Jr were stable over 5 h of incubation under standard conditions. Ji was 106 +/- 4 nequiv min-1 cm-2 and Jr was 39.8 +/- 1.1 nmol O2 min-1 cm-2 (mean +/- S.E., n = 46). Ji was varied with several agents known to affect ion transport across the tracheal epithelium. Na+ absorption was inhibited partly with amiloride or completely following Na+ substitution with choline. Cl- secretion was selectively suppressed by furosemide. Ji was also reduced to a very low level, using ouabain or K+ suppression to inhibit the Na+-K+-ATPase. All these manoeuvres resulted in significant reductions of both Ji and Jr. Basal Jr was not affected when Ji was modified. A plot of the relative change in suprabasal Jr versus the relative change of Ji gave a straight line (r = 0.98, n = 60). A plot using absolute values yielded a stoichiometric ratio of 13.9 ions per O2 molecule, for Na+ as well as for Cl-. The stoichiometric ratio was also calculated for each experiment. Its mean value was 14.9 ions per O2 molecule. The population of the ratios was widely dispersed, but this was explained as a predictable statistical phenomenon.

Biochemical Characterization of Chlorophyll-Free Mitochondria From Pea Leaves

Mitochondria from pea leaves were purified by centrifugation on a self-generated Percoll gradient which contained a linear gradient of polyvinylpyrrolidone-25 (0-10%, w/v). The chlorophyll content of the purified mitochondria was less than 1 �g per mg protein. All substrates were rapidly oxidized by these mitochondria, the rate of glycine oxidation being between 200 and 300 nmol O2 min-1 mg-1 protein, depending on the age of the leaves used. These rates did not vary significantly over a period of 20 h, provided NAD+ was supplied exogenously, when the mitochondria were stored on ice. Respiratory control, ADP/O ratios and outer membrane integrity (always more than 95%) were also maintained during storage. The phospholipid composition of the membranes from the leaf mitochondria was virtually identical to that of mitochondria from non-photosynthetic tissues although their lipid to protein ratio was slightly lower. The polypeptide pattern of the membranes from green leaf mitochondria and those from etiolated leaves and hypocotyls were also similar, but marked differences were observed between the matrix proteins from the different tissues. In particular, intensely stained bands at 94, 51,41 and 15.5 kDa which were present in the matrix of green leaf mitochondria were missing or present in much smaller quantities in the non-photosynthetic tissues. This difference was correlated with the ability of the mitochondria to oxidize glycine, suggesting that the four polypeptides may be associated with the glycine decarboxylase complex.

Direct evidence for the presence of a rotenone‐resistant NADH dehydrogenase on the inner surface of the inner membrane of plant mitochondria

Submitochondrial particles (SMP) were produced from Jerusalem artichoke (Helianthus tuberosus L.) mitochondria by sonication and differential centrifugation. The SMP were about 50% inside‐out as measured by the access of reduced cytochrome c to cytochrome c oxidase. Uncoupled NADH oxidation (1 mM NADH) by the SMP was 120 nmol O2 min−1mg−1, which was reduced to 98 nmol O2 min−1 (mg mitochondrial protein)−1 in the presence of EGTA. In contrast, the oxidation of NADH by intact mitochondria was completely inhibited by EGTA (from 182 to 14 nmol O2 min−1mg−1). The EGTA‐resistant NADH oxidation by the SMP is ascribed to the NADH dehydrogenase(s) on the inside of the inner membrane and exposed to the medium in the inside‐out SMP. In the presence of EGTA it could be shown that two NADH dehydrogenase activities were present in the SMP. One had an apparent Km of 7 μM for NADH, a Vmax of 80 nmol NADH min−1mg−1, and was rotenone‐sensitive. This dehydrogenase is equivalent to the mammalian Complex I NADH dehydrogenase. The other dehydrogenase, which was rotenone‐resistant, had a Km of 80 μM and a Vmax of 131 nmol NADH min−1mg−1; it is probably responsible for the rotenone‐resistant oxidation of organic acids often observed in plant mitochondria. The redox poise of the pyridine nucleotides had only a small effect on the relative rates of the two internal dehydrogenases. Electron flow through these dehydrogenases appears, therefore, to be regulated mainly by the concentration of NADH in the matrix of the mitochondria.

Differential Effects of Inhibitors on Respiratory Activity of Synchronous Cultures of Bacillus subtilis Prepared by Continuous-flow Centrifugation

Size selection by continuous-flow centrifugation was used to prepare synchronous cultures of Bacillus subtilis. A selection of 5–10% was required to yield cultures which gave synchrony indices of about 0·45. Respiration rates [nmol O2 min−1 (ml culture)−1] of cells growing in the presence of glucose rose discontinuously as two steps in each cell cycle with the mid-points of the rises centred at 0·37 and 0·87 of a cycle. An asynchronous control culture exhibited no such periodicities. Two inhibitors of energy conservationN,N′-dicyclohexylcarbodi-imide and 4-chloro-7-nitrobenzofurazaninhibited respiration maximally at 0·0 and 0·6 of a cycle whilst an inhibitor of respiration2-heptyl-4-hydroxyquinoline-N-oxideexerted maximal effect only at 0·4 of a cycle. These results are compared with other temporal events which have been reported to occur during the cell cycle of B. subtilis.

Balance between Cyanide‐Sensitive and ‐Insensitive Respiration in Wheat Root Mitochondria, as Influenced by Salt Concentration in the Plant Growth Medium

AbstractMitochondria were isolated from 7‐day‐old wheat roots (Triticum vulgare Vill. cv. Svenno Spring Wheat) grown in either a full‐strength culture medium (100%) or in the same medium diluted 100 times (1%). Outer membrane integrity was assayed using the cytochrome c reduction assay. This indicated about 20% damage. Using an oxygen electrode the respiration of the mitochondria was measured with either malate or succinate as the substrate (both 40 mM). KCN (3 mM) and salicylhydroxamic acid (SHAM, 1 mM) were used as inhibitors. The properties of the isolated mitochondria (STATE 3 rate, ADP/O ratio, and KCN‐sensitivity) depend upon the ionic concentration of the growth medium of the roots. In the mitochondria isolated from roots grown in the 1% medium (1% mitochondria) there is a synergistic effect of KCN and SHAM. This means that electrons can be shifted from one pathway to the other when only one of the inhibitors is added. This flexibility between the electron pathways is almost nil in the mitochondria isolated from roots grown in the 100% medium (100% mitochondria). The maximal capacity of the alternative electron pathway (= rate in the presence of KCN) is higher in 1% (40 nmol O2 min−1 (mg protein)−1) than in 100% mitochondria (20 nmol O2 min−1 (mg protein)−1. In 100% mitochondria the alternative pathway seems to be operating at maximal capacity in the absence of KCN with both substrates and in both STATES 3 and 4. In 1% mitochondria the alternative pathway functions at >50% of its capacity in the absence of KCN.