Bicarbonate Excess Research Articles

Plasma water as a diagnostic tool in the assessment of dehydration in children with acute gastroenteritis

Acute gastroenteritis is common in childhood. The estimation of the degree of dehydration is essential for management of acute gastroenteritis. Plasma water was assessed as a diagnostic tool in children with acute gastroenteritis and dehydration admitted to hospital. In a prospective cohort study, 101 patients presenting at the emergency department with dehydration were included. Clinical assessment, routine laboratory tests, and plasma water measurement were performed. Plasma water was measured as a percentage of water content using dry weight method. During admission, patients were rehydrated in 12 h. Weight gain at the end of the rehydration period and 2 weeks thereafter was used to determine the percentage of weight loss as a gold standard for the severity of dehydration. Clinical assessment of dehydration was not significantly associated with the percentage of weight loss. Blood urea nitrogen (r = 0.3, p = 0.03), base excess (r =-0.31, p = 0.03), and serum bicarbonate (r = 0.32, p = 0.02) were significantly correlated with the percentage of weight loss. Plasma water did not correlate with the percentage of weight loss. On the basis of the presented data, plasma water should not be used as a diagnostic tool in the assessment of dehydration in children with acute gastroenteritis.

Acid generation upon thermal concentration of natural water: The critical water content and the effects of ionic composition

Thermal evaporation of a variety of simulated pore waters from the region of Yucca Mountain, Nevada, produced acidic liquids and gases during the final stages of evaporation. Several simulated pore waters were prepared and then thermally distilled in order to collect and analyze fractions of the evolved vapor. In some cases, distillates collected towards the end of the distillation were highly acidic; in other cases the pH of the distillate remained comparatively unchanged during the course of the distillation. The results suggest that the pH values of the later fractions are determined by the initial composition of the water. Acid production stems from the hydrolysis of magnesium ions, especially at near dryness. Near the end of the distillation, magnesium nitrate and magnesium chloride begin to lose water of hydration, greatly accelerating their thermal decomposition to form acid. Acid formation is promoted further when precipitated calcium carbonate is removed. Specifically, calcium chloride-rich pore waters containing moderate (10–20 ppm) levels of magnesium and nitrate and low levels of bicarbonate produced mixtures of nitric and hydrochloric acid, resulting in a precipitous drop in pH to values of 1 or lower after about 95% of the original volume was distilled. Waters with either low or moderate magnesium content coupled with high levels of bicarbonate produced slightly basic fractions (pH 7–9). If calcium was present in excess of bicarbonate, waters containing moderate levels of magnesium produced acid even in the presence of bicarbonate, due to the precipitation of calcium carbonate. Other salts such as halite and anhydrite promote the segregation of acidic vapors from residual basic solids. The concomitant release of wet acid gas has implications for the integrity of the alloys under consideration for containers at the Yucca Mountain nuclear waste repository. Condensed acid gases at very low pH, especially mixtures of nitric and hydrochloric acid, are capable of corroding even alloys, such as nickel-based Alloy 22, which are considered to be corrosion-resistant under milder conditions.

Preferential dissolution of carbonate shells driven by petroleum seep activity in the Gulf of Mexico

Authigenic carbonates are common at deep-sea petroleum seeps as a result of excess bicarbonate production during microbial degradation of hydrocarbons coupled to sulfate reduction. Consequently, these seep environments are supersaturated with respect to carbonates. This finding conflicts with taphonomic data that dissolution is the most pervasive mode of shell alteration at seeps. We provide here the first study linking the preservational process with the chemical characterization of the taphonomically-active zone at petroleum seep sites. This characterization is made possible using fine-scale porewater carbonate chemistry data and skeletal material deployed for 8 years at petroleum seep sites in the northwestern Gulf of Mexico. Microelectrode measurements of pH and pCO 2 identify a very restricted zone of CaCO 3 undersaturation immediately below the sediment–water interface in otherwise supersaturated environments (i.e., sandwiched between supersaturated bottom seawater and sediment porewater). This zonation characterizes the taphonomically-active zone, and is a result of a highly compressed redox front between acid-generating aerobic oxidation of reduced chemical species including hydrocarbons, H 2S, and planktonic-and-terrestrial organic carbon and base-generating sulfate reduction coupled to CH 4 oxidation. Porewater geochemistry is spatially variable at seep sites, and produces variable shell-dissolution signatures. Shells deployed at seep sites have moderate to severe dissolution that is consistent with a much higher flux of total dissolved inorganic carbon (DIC) from the porewater to the bottom water. Therefore, a mosaic of preservational conditions is directly related to the spatially and chemically varying taphonomically-active zones found at seep sites. These findings support the variability of carbonate preservation reported for globally-distributed Phanerozoic fossil seeps and the view that data from field taphonomy can significantly upgrade and validate carbonate destruction rates used in geochemical and climatic models. Carbon mass-balance analyses also lead to an important conclusion that carbonate dissolution forms a very important mechanism for benthic carbon recycling, possibly accounting for 50% of the benthic DIC flux to the bottom water in northern Gulf of Mexico petroleum seep sediments.

Phototrophic utilization of taurine by the purple nonsulfur bacteria Rhodopseudomonas palustris and Rhodobacter sphaeroides.

Taurine metabolism by two phototrophically grown purple nonsulfur bacteria enrichment isolates has been examined. Rhodopseudomonas palustris (strain Tau1) grows with taurine as a sole electron donor, sulfur and nitrogen source during photoautotrophic growth. Rhodobacter sphaeroides (strain Tau3) grows on the compound as sole electron donor, sulfur and nitrogen source, and partial carbon source, in the presence of CO(2) during photoheterotrophic growth. Both organisms utilize an inducible taurine-pyruvate aminotransferase and a sulfoacetaldehyde acetyltransferase. The products of this metabolism are bisulfite and acetyl phosphate. Bisulfite ultimately was oxidized to sulfate, but this was not an adequate source of electrons for photometabolism. Experiments using either [U-(14)C]taurine or (14)CO(2) demonstrated that Rb. sphaeroides Tau3 assimilated the carbon from approximately equimolar amounts of taurine and exogenous CO(2). The taurine-carbon assimilation was not diminished by excess non-radioactive bicarbonate. Malate synthase (but not isocitrate lyase) was induced in these taurine-grown cells. It is concluded that assimilation of taurine carbon occurs through an intermediate other than CO(2). Similar labelling experiments with Rp. palustris Tau1 determined that taurine is utilized only as an electron donor for the reduction of CO(2), which contributes all the cell carbon. Photoautotrophic metabolism was confirmed in this organism by the absence of either malate synthase or isocitrate lyase in taurine+CO(2)-grown cells. Culture collection strains of these two bacteria did not utilize taurine in these fashions.

Iron uptake in a bicarbonate-resistant cell line of tobacco

In alkaline soils, plant growth is impaired mainly by high pH and high concentration of bicarbonates. The bicarbonate concentration increases the pH value, and causes deficiency of iron. A bicarbonate-resistant cell line (BR line) of tobacco (Nicotiana tabacum L. cv. Burley21) was selected by adding excess bicarbonate ions (20 mmol L−1) to the culture medium. The pH of the medium was buffered 8.0 to 8.3. Under these conditions, about 80% of iron in the medium became insoluble. However, under such conditions, the BR line grew well. In this report, we examined some characteristics of the growth and iron uptake in the BR line under iron-deficient (i.e. high pH or no-iron) condition. At pH 5.8, the Fe3+ reduction activity was not significantly different between the non-selected line and the BR line. At pH 8.0, however, the Fe3+ reduction activity of the BR line was higher than that of the non-selected line. In no-iron condition, the growth of the non-selected line was markedly reduced after 2 weeks, while the BR line was not affected. The content of malic acid in both lines increased with the medium pH, and the content in the BR line was higher than that in the non-selected line. The BR line was able to adapt to the conditions, which restricted iron uptake, such as high bicarbonate concentration, high pH, and low iron conditions. The high ability of Fe3+ reduction was maintained at even high pH conditions. Further, the BR line may be able to improve the utilization of iron in the cells.

Changes in soils irrigated with saline groundwater containing excess bicarbonate

Changes in soil properties caused by irrigation with saline groundwater (approx. 2 dS/m) containing excess bicarbonate were measured on Vertosols and Sodosols in the West Wimmera, Victoria, Australia. Irrigation caused soil pH to increase, and where this had risen sufficiently (approx. 8.0), the sodium absorption ratio (SAR) of 1 : 5 soil extracts also increased, presumably due to precipitation of calcium and magnesium carbonates. Salt only accumulated when the SAR of 1 : 5 soil extracts was high. In contrast to previous studies, SAR of the soil extracts was not correlated with exchangeable sodium percentage (ESP) of the exchange complex, nor with soil pH. SAR values rose with irrigation once pH exceeded 8, suggesting that carbonate formation was incomplete due to insufficient bicarbonate. The results imply that gypsum application may ameliorate soil properties even if amounts applied are not sufficient to alter ESP.

Minimal-invasive approach to study pulmonary, metabolic and renal responses to alimentary acid-base changes in conscious rabbits.

Systemic acid-base balance is maintained by the complex interplay of renal and pulmonary control functions and metabolic adaptations, whereby intake and mineral composition of feed are important factors. It was intended to explore the role of alimentary acid-base load and carbonic anhydrase activity for regulatory responses of renal, pulmonary or metabolic origin in rabbits as typical herbivores. Sixty-eight conscious male rabbits (about 3.5 kg) were kept in a metabolic cage, to determine daily water intake, urine excretion and food consumption. Different groups were fed either alkali-rich rabbit standard pellets, or modified rabbit chow with low Ca++-content, or a special diet with very low alkali content, or standard food together with a low oral dose (about 20 mg x kg(-1) x d(-1)) acetazolamide. Samples from the central ear artery were analyzed for blood gases (PaO2, PaCO2), pHa, base excess (BE) and actual bicarbonate (HCO3a-). The metabolic CO2 production (VCO2 STPD) was determined, to calculate alveolar ventilation (VA BTPS). Anaerobically collected urine was analyzed for pHu and for concentrations of bicarbonate/carbonate (HCO3-/CO3--), ammonium (NH4+), and phosphate. 1) Systemic BE was not affected by alimentary alkali load, either varied spontaneously by standard food intake or by the low-Ca++ diet, and decreased only slightly on the low-alkali diet, but distinctly upon carbonic anhydrase inhibition. 2) Under all conditions of alimentation, PaCO2 was closely correlated with BE without a detectable set-point, the normal-range variability of BE being sufficient to elicit corresponding changes in VA. In contrast, acetazolamide led to much lower values of PaCO2 than predicted by the reference PCO2/BE relationship, being primarily caused by significant reductions in VCO2 (> 20%). 3) Prior to other systems, renal base excretion, normally being high on species-adapted standard chow, closely followed any variation of alimentary alkali load and approached zero upon the low-alkali diet. It was, however, not significantly influenced by carbonic anhydrase (CA) inhibition on alkalirich alimentation. Blood acid-base balance in rabbits is maintained over a wide range of alimentary alkali load by effective adaptation of renal base excretion, independent of CA activity. Ventilatory pH control is perpetuated even in the normal range of BE, provided metabolic rate is not impaired, e. g., by CA inhibition. These results may help one understand the different manifestations of acid-base disorders in body fluids under clinical conditions.

Effects of bicarbonate, nitrate and other environmental factors on iron deficiency chlorosis. A review

The influence of several environmental factors on the occurrence of iron deficiency chlorosis on calcareous soils, also called bicarbonate induced chlorosis, is described. Bicarbonate in the soil solution is a strong pH buffer, mainly in the presence of calcium carbonate. Since bicarbonate is quite mobile, and CO2 diffusion is a slow process, the pH decrease in such soils after proton release by plants is small. Also, the ferric reductase activity of plant roots declines sharply at high pHs. The chemical Fe(III) reduction depends on the pe+pH; so, the lower the pH, the more favored is the formation of Fe(II) from the Fe(III) in the rizosphere. Nitrate can be acquired by the roots along with a proton cotransport that increase the pH outside the root plasmalemma, but a redox effect may be also important. In the rizosphere, the conditions for the reduction of nitrate (N(V)) to nitrite (N(III)) and ammonia (N(‐III)) are attained before than the conditions for the Fe(III) reduction from a solid phase. So, from the thermodynamic point of view, the electrons released by the plant can be taken directly by nitrate instead of Fe(III), or the Fe(II) formed can be reoxidized by the nitrate. Furthermore, if nitrate and nitrite reductions occurs in the rizosphere, microsite pH increases at the root surface. Since controversial data have been reported on the pH variations in the xylem sap in the presence of an excess of bicarbonate in the medium, a slower transport of iron does not appear to be the main reason for bicarbonate induced chlorosis. The “iron paradox” is well known (Römheld, 1987): sometimes, in soil culture, chlorotic leaves can have higher iron concentration than green ones. Some authors suggest that bicarbonate may affect the Fe distribution within the leaves. Apoplastic pH would control the entry of iron to the cytosol in leaves in a similar way than occurs in the root. Bicarbonate in the nutrient solution could act as a buffer in the leaf apoplast. Nitrate uptake in the meristem also produces a pH increase, with the same effect than the bicarbonate. Also, nitrate is an oxidant that could reduce the availability of the electrons for the Fe reduction for the membrane transport.

The Reaction of Melatonin with Peroxynitrite: Formation of Melatonin Radical Cation and Absence of Stable Nitrated Products

Peroxynitrite is capable of hydroxylating and nitrating aromatic species. However, nitromelatonin is not found as a final product when melatonin was allowed to react with peroxynitrite either in the presence or absence of added bicarbonate. In the absence of bicarbonate, the two major products formed are 6-hydroxymelatonin and 5-methoxy-2-hydro-pyrroloindole, and the latter is the only major product with excess bicarbonate. A transient purple intermediate with a maximum absorbance at about 520 nm is observed upon mixing solutions containing peroxynitrite and melatonin. These observations indicate that the melatoninyl radical cation is formed in the peroxynitrite/melatonin reaction, providing a direct evidence for the one-electron oxidation ability of peroxynitrite. The melatoninyl radical cation also is observed with excess bicarbonate.

Kinetic studies on the removal of iron and aluminum from recombinant and site-directed mutant N-lobe half transferrins.

Kinetic studies have been conducted in pH 7.4 Hepes buffer at 25 degreesC on the removal of Fe(III) and Al(III) from the recombinant N-lobe half molecule of human serum transferrin (Tf/2N) and from the R124A, K206A, and K296A mutants of this protein. The rates of iron removal from Tf/2N by 3-hydroxypyridin-4-one (deferiprone) and nitrilotriacetic acid (NTA) are essentially identical with previous results on N-terminal monoferric transferrin (Tf-FeN). For both Tf/2N and Tf-FeN, iron removal by deferiprone follows simple saturation kinetics, while iron removal by NTA follows simple first-order kinetics. There is some discrepancy between the two proteins with respect to iron removal by PPi, but this may be due to differences in the chloride concentrations among different studies. The addition of Fe(NTA)2 to R124A at ambient bicarbonate concentrations forms the Fe-NTA-Tf ternary complex, but the usual Fe-CO3-Tf complex can be formed by adding ferrous ion in the presence of a larger excess of bicarbonate. This complex releases its iron very rapidly by a mechanism that is first-order with respect to the ligand. This suggests that the first-order component of metal release from transferrin involves the displacement of the synergistic carbonate anion. Since iron removal from K206A and K296A at pH 7.4 is extremely slow, studies have been conducted on the more labile Al3+ complexes of Tf/2N, K206A, and K296A. The removal of Al3+ from Tf/2N by PPi follows the same complex kinetic order with respect to the ligand concentration that is observed for iron removal, while the removal of Al3+ from both K206A and K296A reverts to a simple saturation process. The addition of perchlorate retards the removal of Al3+ from both K206A and K296A, suggesting that these lysine residues are not associated with the allosteric effects of inorganic anions on the rates of metal removal.

The behavior of polyprotic anions in ion-exchange resins

After observing that pH dropped dramatically when chloride-form strong-base anion resins were contacted with neutral and alkaline solutions of bicarbonate and arsenate anions, three representative strong-base resins were tested for their ability to produce pH changes. It was discovered that all three chloride-form resins could convert HCO 3− − to CO 3 2−, and H 2AsO 4 − to HAsO 4 2− with the expulsion of protons, a decrease in pH, and an increase in the ionic concentration of the aqueous phase. For bicarbonate which can give up and take up protons, the following reaction was observed: 2 R 4N +Cl − + HCO − 3 ⇔ (R 4N +) 2CO 3 + Cl − + H +Cl − Depending on the local concentration of excess bicarbonate, the HCl produced either remained as HCl or reacted to form carbonic acid in a reaction which tended to buffer the system. The resin characteristics related to its preference for divalent ions and its ability to produce higher-valent anions by proton expulsion were (a) appropriate functional group charge spacing, (b) ability to reorient functional groups to satisfy polyvalent ions, and (c) presence of hydrogen-bonding hydrophilic groups such as carbonyl and hydroxyl. IkA-458, the resin that was clearly superior in its ability to produce higher-valent ions, exhibits the highest divalent selectivity, is hydrophilic, and carries its quaternary amine functional groups at the end of a long flexible pendant arm containing an amide bond with hydrogen-bonding potential. Implications of the experimental findings as applied to arsenate removal from water are discussed.

Effects of mutations of aspartic acid 63 on the metal-binding properties of the recombinant N-lobe of human serum transferrin.

Mutations of the aspartic acid residue at position 63 of the N-lobe of human serum transferrin substantially alter the metal ion- and anion-binding properties of the protein. Substitution of serine, asparagine, glutamic acid, or alanine results in the loss of a key component of the interface in the interdomain cleft and the metal-binding ligand, aspartic acid, leading in all cases to an increased preference for NTA rather than carbonate as the "synergistic" anion relative to the wild-type protein. Excess bicarbonate is required to eliminate the NTA and obtain the "correct" visible spectrum. Carbonate replaces NTA via an intermediate. Blue shifts for the characteristic absorption band of each mutant show a range of effects on the Fe-O (Tyr) interaction. Titration with Co(III) yielded the molecular absorption coefficient for each mutant except D63A, where Co(III) appeared to oxidize the tyrosine residues and damage the ability of the mutant to bind metal. The chelator, Tiron, removes iron from hTF/2N with a simple saturation kinetic mode with respect to the ligand concentration. Chloride inhibits the release in an interesting manner: the effect is initially sharp and then levels off with a minimum k(obs) at [KCl] = 0.5 M. However, the reaction of the D63 mutants with Tiron results in the formation of the ternary complexes Fe-hTF/2N-Tiron. Significant red shifts for the characteristic absorption bands of these complexes suggest a different ligation of Tiron in the mutants from that in wild-type hTF/2N.

Effect of pH on growth and carbon metabolism of maltose-releasing Chlorella (Chlorophyta)

The effect of low pH on growth and photosynthesis was compared in two strains of Chlorella isolated from symbiosis with Paramecium bursaria. One, 3N813A, releases large amounts of maltose at low pH; the other, NC64A, does not release maltose in culture. Maltose synthesis at low pH appeared to have a greater effect on cell growth than pH by itself. Growth of maltose-releasing 3N813A showed a direct relationship with pH; growth of non-maltose-releasing NC64A was reduced only as pH fell from 7.0 to 5.5. At pH 5.0, net photosynthetic capacity of 3N813A cells was reduced to 76% of controls at pH 7.0, but the specific growth constant (k) was reduced to 22%, and at pH 4.0 growth and nitrate uptake were inhibited. In 3N813A cells at pH 5.0, carbon (C) was diverted from cell growth, net chlorophyll synthesis, assimilation of nitrogen (N), and synthesis of protein and starch to maltose release, but C:N ratios were unchanged. In NC54A cells, starch but not protein synthesis was inhibited at pH 5.0, and a reduction in accumulation of N led to an increase in C:N ratios. Unlike N starvation, growth of 3N813A cells at pH 5.0 did not reduce chlorophyll content. When measured at pH 7.0 with excess bicarbonate, photosynthetic parameters of both 3N813A and NC64A cells grown at pH 5.0 were similar to those of cells grown at pH 7.0; however, net photosynthesis of 3N813A cells N starved at pH 7.0 was 22% of that of N-sufficient controls. In symbiosis, release of excess photosynthate as maltose may inhibit cell growth by inhibiting assimilation of inorganic N, but because C:N ratios are unchanged, photosynthetic capacity of cells is not affected.

Effect of pH on growth and carbon metabolism of maltose-releasing Chlorella (Chlorophyta)

The effect of low pH on growth and photosynthesis was compared in two strains of Chlorella isolated from symbiosis with Paramecium bursaria. One, 3N813A, releases large amounts of maltose at low pH; the other, NC64A, does not release maltose in culture. Maltose synthesis at low pH appeared to have a greater effect on cell growth than pH by itself. Growth of maltose-releasing 3N813A showed a direct relationship with pH; growth of non-maltose-releasing NC64A was reduced only as pH fell from 7.0 to 5.5. At pH 5.0, net photosynthetic capacity of 3N813A cells was reduced to 76% of controls at pH 7.0, but the specific growth constant (k) was reduced to 22%, and at pH 4.0 growth and nitrate uptake were inhibited. In 3N813A cells at pH 5.0, carbon (C) was diverted from cell growth, net chlorophyll synthesis, assimilation of nitrogen (N), and synthesis of protein and starch to maltose release, but C:N ratios were unchanged. In NC54A cells, starch but not protein synthesis was inhibited at pH 5.0, and a reduction in accumulation of N led to an increase in C:N ratios. Unlike N starvation, growth of 3N813A cells at pH 5.0 did not reduce chlorophyll content. When measured at pH 7.0 with excess bicarbonate, photosynthetic parameters of both 3N813A and NC64A cells grown at pH 5.0 were similar to those of cells grown at pH 7.0; however, net photosynthesis of 3N813A cells N starved at pH 7.0 was 22% of that of N-sufficient controls. In symbiosis, release of excess photosynthate as maltose may inhibit cell growth by inhibiting assimilation of inorganic N, but because C:N ratios are unchanged, photosynthetic capacity of cells is not affected.

Excess sodium bicarbonate in the diet and its effect on Leghorn chickens.

1. A commercial 62-week-old layer flock experienced an acute drop in egg production and an increase in shell-less egg production within 2 days of consuming feed erroneously formulated to contain over 30 g/kg instead of 3 g/kg sodium bicarbonate (NaHCO3). Other symptoms included increased water consumption, diarrhoea and increased mortality associated with visceral gout. 2. An experiment was conducted to assess the responses of hens under controlled conditions. Twenty Dekalb XL Single Comb White Leghorn hens (50 weeks old) were placed in individual cages, having ad libitum access to water from trough waterers. Ten hens were fed the TEST (High NaHCO3) feed for one week (Test group), and ten hens remained on normal commercial layer ration (Control group). 3. Hens in the Test group had high water consumption and watery droppings, but egg production and mortality were not affected. Physiological evaluations indicated the Test feed caused metabolic alkalosis. Plasma sodium, urine pH and urinary sodium excretion were increased, and glomerular filtration rates were decreased in the Test group. 4. These physiological effects are consistent with known responses to excess sodium intake in domestic fowl. The reduced egg production and increased mortality caused by the Test feed under commercial conditions may be related to more severe dehydration experienced by hens in multi-bird cages supplied by cup-type watering systems.

Bicarbonate Concentration by Synechocystis PCC6803

The ability of the cyanobacterium Synechocystis PCC6803 to transport inorganic carbon in the form of bicarbonate rapidly decreased following a shift from bicarbonate-limited growth to either excess bicarbonate supply or to photoheterotrophic growth on glucose. Nonmetabolizable analogs of glucose did not exert this effect. The rate at which the bicarbonate uptake rate declined was too rapid to be accounted for by dilution of the activity by culture growth and suggested that posttranslational modification may be involved. Several proteins that were unphosphorylated during bicarbonate-limited growth became phosphorylated during the shifts to high CO(2) conditions and to photoheterotrophic growth. A similar alteration in the profile of phosphopolypeptides was observed following a shift into the dark. The changes in protein phosphorylation were not blocked by chloramphenicol or rifampicin.

Calorimetric studies of the binding of ferric ions to ovotransferrin and interactions between binding sites

Transferrins are two-domain proteins with a very strong site for iron binding located in each domain. Using ultrasensitive titration calorimetry, the binding of ferric ion (chelated with a 2-fold molar excess of nitrilotriacetate) to the two sites of ovotransferrin was studied in detail as well as the binding to the single site in the N- and C-terminal half-molecules. In the presence of excess bicarbonate ion, the binding occurs in two kinetic steps. The fast process of contact binding is instantaneous with respect to instrument response time, is strongly exothermic for the N site and less so for the C site, and corresponds to binding of the chelated ferric ion. The slower process of bicarbonate insertion with concomitant release of nitrilotriacetate occurs on a time scale of 2-20 min over the temperature range 7-37 degrees C and is endothermic for the N site and exothermic for the C site, with rates being significantly slower for insertion at the C site. The delta H of binding is strongly temperature-dependent for both sites, arising from a large negative delta Cp of binding which probably indicates removal of hydrophobic groups from contact with water. When bicarbonate ion is absent, only the fast process of contact binding is seen. Each site within a half-molecule is qualitatively similar to the same site in intact ovotransferrin, although quantitative differences were detected. It was shown that contact binding to ovotransferrin occurs reversibly with free exchange of Fe+3 between N and C sites, while the attachment to either site becomes essentially irreversible after bicarbonate insertion. The strong preference for the first ferric ion to bind to the N site is shown to be due to its larger contact binding constant and the faster rate of bicarbonate insertion, relative to the C site, and is not due to stronger thermodynamic binding after bicarbonate insertion. True equilibrium is achieved only over much longer periods of time. In another series of experiments, direct binding studies were carried out between the two half-molecules under different states of ligation with Fe+3 in the presence of bicarbonate. The results indicate that the two binding sites in ovotransferrin, separated by ca. 40 A, are not independent of one another but communicate as a result of ligand-dependent changes in the heats and free energies of domain-domain interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Is urea formation regulated primarily by acid-base balance in vivo?

Large quantities of ammonium and bicarbonate are produced each day from the metabolism of dietary protein. It has recently been proposed that urea synthesis is regulated by the need to remove this large load of bicarbonate. The purpose of these experiments was to test whether the primary function of ureagenesis in vivo is to remove ammonium or bicarbonate. The first series of rats were given a constant acid load as hydrochloric acid or ammonium chloride; individual rats received a constant nitrogen load at a time when their plasma acid-base status ranged from normal (pH 7.4, 28 mM HCO3) to severe metabolic acidosis (pH 6.9, 6 mM HCO3). Urea plus ammonium excretions and the blood urea, glutamine, and ammonium concentrations were monitored with time. Within the constraints of non-steady-state conditions, the rate of urea synthesis was constant and the plasma glutamine and ammonium concentrations also remained constant; thus it appears that the rate of urea synthesis was not primarily regulated by the acid-base status of the animal in vivo over a wide range of plasma ammonium concentrations. In quantitative terms, the vast bulk of the ammonium load was converted to urea over 80 min; only a small quantity of ammonium appeared as circulating glutamine or urinary ammonium. Urea synthesis was proportional to the nitrogen load. A second series of rats received sodium bicarbonate; urea synthesis was not augmented by a bicarbonate load. We conclude from these studies that the need to dispose of excess bicarbonate does not primarily determine the rate of ureagenesis in vivo. The data support the classical view that ureagenesis is controlled by the quantity of ammonium to be removed.

The maintenance of metabolic alkalosis: Factors which decrease bicarbonate excretion

AbstractMetabolic alkalosis is a primary rise in the concentration of bicarbonate in extracellular fluid and can be divided into two phases: generation and maintenance. Generation requires either the loss of acid or the addition of bicarbonate to the circulation. Most clinical forms of the disorder are associated with the loss of acid, either through the gastrointestinal tract (gastric alkalosis is the classic example) or in the urine; the most common example of the latter type of generation is diuretic-induced metabolic alkalosis. Metabolic alkalosis is usually maintained because the kidney fails to excrete the extra bicarbonate added to the extracellular fluid compartment via the two mechanisms just mentioned. This review is concerned with the factors that prevent the kidney from excreting the excess bicarbonate present in subjects with metabolic alkalosis.

Nitrogen and bicarbonate relationships with iron nutrition in plants

Abstract Bicarbonate levels in soils or in irrigation waters have often been implicated as a most important parameter in the induction of line‐induced chlorosis. If borderline deficiency is present, the addition of nitrogen also induces the deficiency. A physiological disorder induced by excess bicarbonate relating to the onset of iron deficiency has been extremely difficult to elucidate. One of the more obvious effects of bicarbonate is the retention of calcium in roots and failure of its translocation to shoots when high levels of it are present in nutrient solutions. Bicarbonate physiologically is metabolized ‐to organic acids in roots. High levels of nitrate nitrogen are also conducive to the synthesis of organic acids in roots and also to increased basicity in the rhizosphere which can be interpreted as result of bicarbonate. Net result in either case is decreased uptake and translocation of iron. In an experiment with PI‐54619–5‐l soybeans, bicarbonate and nitrate gave similar patterns of chlorosis ...