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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Each mole of oxyhemoglobin iron converted to methemoglobin causes the oxidation of 1.5 mol of nitrite to nitrate and consumes 1 mol of protons. No oxygen is liberated. The overall reaction has two simultaneously occurring parts. In the beginning the rate-limiting reaction converting O2Hb to metHb is directly proportional to H+ and NO2- concentrations and is independent of metHb. The second portion accounts in major part for the stoichiometry and rate of the overall reaction. In this portion O2Hb tetramers and metHbNO2- are the reactants. Essentially no reaction takes place in the presence of CN-, which displaces nitrite from the metHbNO2-, nor in the presence of 0.5 mol/liter Nal, which converts the O2Hb to alphabeta-dimers. The autocatalytic nature of the overall reaction in the presence of excess nitrite is the result of metHb, which is formed in both parts of the reaction, associating with nitrite to increase the concentration of one reactant of the cyanide-sensitive part. The reaction rates at constant pH in excess nitrite are porportional to the product of the O2Hb concentration and the square of the metHb concentration. The rate increases up to about 66% conversion of O2Hb followed by a decrease as the O2Hb becomes limiting. The dissociation constant of metHbNO2- at 25 degrees C and pH = 6.4 was found to be 1.11+/-0.11 mmol/liter.
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PMID:A mechanism for the conversion of oxyhemoglobin to methemoglobin by nitrite. 1 98

Molar growth yields, fermentation balances and enzyme activities were measured in Veillonella alcalescens grown anaerobically with different substrates in the absence or presence of fumarate or nitrate. The molar growth yields on malate (14.3 g dry wt bacteria/mole substrate) and citrate (19.3) were higher than that on lactate (8.6). The molar growth yield on lactate was increased to 15.5 or 19.8 by the addition of fumarate or nitrate, respectively, to the growth medium, and the molar growth yield on citrate was increased to 25.3 by addition of nitrate. Active growth on pyruvate was only observed in the presence of nitrate, and the molar growth yield was 25.5. From fermentation balances and fermentation systems similar YATP values (g dry wt bacteria/mole ATP) were calculated for all substrates or mixtures of substrates assuming that one mole of ATP is generated at the electron transport from pyruvate, NADH and NADPH to nitrate or fumarate whereas ATP is not produced in the electron transport from lactate to fumarate or nitrate, and, therefore, this assumption was considered to reflect the actual situation. The mean YATP value at a doubling time of 1 h was 16.5 g dry wt bacteria/mole ATP for growth without an added hydrogen acceptor, 14.4 for growth with fumarate, and 14.2 for growth with nitrate.
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PMID:ATP formation associated with fumarate and nitrate reduction in growing cultures of Veillonella alcalescens. 20 92

Anaerobic growth of E. coli, strain K-10, depending on formate oxidation by nitrate, fumarate, and trimethylamine N-oxide was followed in a medium containing peptone. The presence of formate and peptone was indispensable for growth with fumarate and trimethylamine N-oxide reduction. While there was no growth in the absence of acceptor, growth was observed in the absence of formate by nitrate reduction though not as much as under aerobic conditions. Per mole consumed formate equimolar succinate or trimethylamine was formed, but 1.2 mole of nitrate was produced, probably depending partly on peptone oxidation. The molar growth yield on formate was found to be 6.5, 7.6, and 7.0 g cells/mole depending on the reduction of nitrate, fumarate, and trimethylamine N-oxide, respectively, suggesting the formation of one mole ATP coupled to the anaerobic electron transfers from formate.
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PMID:Anaerobic growth of Escherichia coli on formate by reduction of nitrate, fumarate, and trimethylamine N-oxide. 32 8

1. Bicarbonate transport across human red cell membranes was studied between 0 and 10 degrees C at alkaline pH values by determining the efflux of 14C-labelled bicarbonate from resealed erythrocyte ghosts. Transfer of labelled CO2 was eliminated as a source of error, when formation of intracellular 14CO2 was inhibited with carbonic anhydrase inhibitors. The study showed that there are no fundamental differences between the characteristics of bicarbonate and of chloride self-exchange as has been inferred from previous studies of chloride-bicarbonate exchange. 2. Efflux of radioactivity could be reduced more than 99% by reversible and irreversible inhibitors of anion transport. Inhibition of both chloride and bicarbonate self-exchange was linearly related to the binding of 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) to the membranes. Complete (i.e. greater than 99%) inhibition was obtained after binding of 1.2 x 10(6) DIDS molecules per cell. 3. Bicarbonate self-exchange proved a saturable function of bicarbonate concentration, with a maximum at external and internal concentrations of approximately 100 mM, showing self-depression at higher bicarbonate concentrations, and half-maximum exchange flux at a concentration of 10 mM. The results were consistent with the hypothesis that the exchange mechanism has two anion binding sites, one mediating ion transport and the other causing transport inhibition. 4. Maximum exchange flux of bicarbonate was about 30% larger thant that of chloride, and the affinity of bicarbonate for the transport site was about three times larger than that of chloride. The apparent activation energy of bicarbonate exchange was 28 kcal/mole, the same order of magnitude as found for other inorganic anions between 0 and 10 degrees C. 5. The ability of other inorganic anions to exchange with bicarbonate decreased in the sequence Cl greater than NO3 greater than F greater than Br greater than or equal to I, corresponding to the sequence of the rate of self-exchange of halides. 6. Counter-transport of bicarbonate could be driven by a chloride gradient, when ghosts containing KCl were suspended in a medium containing traces of labelled bicarbonate in addition to a non-permeating anion. Concentration ratios (ci/co) up to about 1000 could be obtained. 7. It is concluded that bicarbonate is transported by the inorganic anion exchange mechanism of the erythrocyte membrane. The slight differences between the exchange kinetics of chloride and bicarbonate were explained by differing affinities of the two anions for the two anion binding sites of the transport system.
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PMID:Bicarbonate exchange through the human red cell membrane determined with [14C] bicarbonate. 51 56

1. The steady-state tracer exchange flux of chloride was measured at 10-150 mM external chloride concentration, substituting either lactate or sucrose for chloride. The chloride flux saturates in both cases with a K 1/2 about 50 and 15 mM, respectively. 2. The inhibitory effect of other monovalent anions on the chloride transport was investigated by measuring the 36Cl- efflux into media where either bromide, nitrate, or thiocyanate had been substituted for part of the chloride. The sequence of increasing affinity for the chloride transport system was found to be: Br- less than Cl- less than SCN- = NO3-. 3. The chloride steady-state exchange flux in the presence of nitrate can be described by Michaelis-Menten kinetics with nitrate as a competitive inhibitor of the chloride flux. 4. The apparent activation energy (EA) was determined to be 67 +/- 6.2 kJ/mole, and was constant between 7 and 38 degrees C. 5. The membrane potential (Vm) was measured as a function of the concentration of external K+, substituting K+ for Na+. The transference number of K+ (tK) was estimated from the slope of Vm vs. log10 (K+)e, and tCl and tNa were calculated, neglecting current carried by ions other than Cl-, K+, and Na+. The diffusional net flux of K+ was calculated from the steady-state exchange flux of 42K+, assuming the flux ratio equation to be valid. From this value the K+ conductance and the Na+ and Cl- conductances were calculated. The experiments showed that GCl, GNa, and GK are all about 14 muS/cm2. 6. The net (conductive) chloride permeability derived from the chloride conductance was 4 x 10(-8) cm/sec compared with the apparent permeability of 6 x 10(-7) cm/sec as calculated from the chloride tracer exchange flux. These data suggest that about 95% of the chloride transport is mediated by an electrically silent exchange diffusion. 7. Comparable effects of phloretin (0.25 mM) on the net (conductive) permeability and the apparent permeability to chloride (about 80% inhibition) may indicate that the chloride exchange and conductance pathways are not completely separate and distinct modes of transport, but may involve common elements. The reduced chloride permeability in the presence of phloretin is estimated to be two orders of magnitude larger than the ground permeability of the cell membrane.
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PMID:Membrane potential, chloride exchange, and chloride conductance in Ehrlich mouse ascites tumour cells. 52 33

The formation of nitrite from nitrate was studied in potatoes incubated at room temperature. After 24 hours of incubation at 25 degrees, 112 ppm and 373 ppm of nitrite formed in homogenized cooked potatoes containing 284 ppm and 584 ppm of nitrate, respectively. In homogenized fresh potatoes incubated at 21 degrees and containing 284 ppm of nitrate, 103 ppm of nitrate formed within 24 hours. During the period of nitrite formation, nitrate levels decreased sharply, indicating that reduction of nitrate to nitrite occurred. Incubation at 2 degrees completely prevented nitrite formation in all cases. The formation of methylnitrosourea from added methylurea and nitrite was observed in potato incubated under simulated gastric conditions (37 degrees, pH 1.5). An ascorbate-nitrite mole ratio of 4 gave a 93% inhibition of methylnitrosourea formation. Ascorbate reacted directly with nitrite in potato incubated under identical conditions, yielding a 43% decrease in nitrite concentration. Ascorbate did not react with methylurea or the product, methylnitrosourea.
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PMID:Reduction of gastric carcinogens with ascorbic acid. 106 Apr 1

When anaerobic cultures of Propionibacterium pentosaceum were shifted to low dissolved-oxygen concentration (D.O.C.), acetate production from lactate diminished and propionate production stopped, whereas pyruvate accumulated and oxygen was consumed. Assuming that energy is generated in the electron transfer to oxygen, YATP values (g dry wt bacteria/mole ATP) of between 7.2 and 11.9 were calculated from molar growth yields and product formation. When oxidative phosphorylation in the electron transfer to oxygen was ignored, unreasonably high YATP values were obtained. From these results it is concluded that energy is indeed generated in the electron transfer to oxygen. However, synthesis of cytochrome b was strongly repressed by oxygen. Furthermore, synthesis of all catabolic enzymes studied was impaired in bacteria growing at low D.O.C. Thus, the anaerobic character of P. pentosaceum may be explained by the inhibition of synthesis of both cytochrome b and enzymes in the presence of oxygen. It was demonstrated that nitrate reductase is synthesized constitutively in P. pentosaceum. Synthesis of nitrate reductase was stimulated by nitrate and repressed by oxygen. Synthesis of fumarate reductase was also repressed by oxygen, whereas only a small effect of nitrate on this enzyme was observed. However, propionate formation is inhibited during growth with nitrate. The absence of propionate formation in the presence of oxygen and nitrate is explained by inavailability of NADH needed for the conversion of oxaloacetate into malate in the reductive pathway to succinate, so that succinate and propionate cannot be formed.
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PMID:Lactate metabolism in Propionibacterium pentosaceum growing with nitrate or oxygen as hydrogen acceptor. 108 38

Yields of Thiobacillus dentrificans on different substrates were compared. The organism was grown in a chemostat at a dilution rate of 0.03 h-1. From the difference in the cell yields with (1) oxygen (6.40 g carbon per mole thiosulphate) and (2) nitrate (4.51 g carbon per mole thiosulphate) as an electron acceptor the experimental value for Y ATP was estimated to be 1.75. The efficiency of the biosynthetic system would be 42% if 1 ATP should be needed in reversed electron transport, and 57% if this was 2 ATP per electron pair. It could be calculated that during anaerobic oxidation of thiosulphate with nitrate 1.41 or 1.16 ATP per 2 electrons are generated if 1 or 2 ATP respectively per thiosulphate is formed in substrate-level phosphorylation. For aerobic oxidation these figures are 2.40 and 2.16, respectively.
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PMID:Energetic aspects of the metabolism of reduced sulphur compounds in Thiobacillus dentrificans. 108 62

The effciency of denitrification, or anaerobic respiration, in Pseudomonas denitrificans was investigated, using growth yield as an index. Glutamate was mainly used as the sole source of energy and carbon. In batch culture, the growth yield per mole of electrons transported through the respiratory system under denitrifying conditions was about half that under aerobic conditions. Similar figures were also obtained in chemostat cultures under glutamate-limited conditions. The decrease in growth yield under denitrifying conditions could be due to the restriction of phosphorylation associated with nitrate reduction to nitrogen gas.
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PMID:Growth yield of a denitrifying bacterium, Pseudomonas denitrificans, under aerobic and denitrifying conditions. 115 26

A new species of Candida podzolica is described. This species is widely distributed in podzolic and soddy-podzolic soils of the forest zone and in krasnozem. The yeast belongs to the nitrate-negative species of the genus Candida Berkhout, which do not ferment sugars, and is similar to the species C. humicola and C. curvata inhabiting soil. C. podzolica has a peculiar shape of the cells and does not produce films in liquid media. Extracellular polysaccharides contain glucose, mannose, galactose, and xylose; G+C in DNA is 62 mole percent.
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PMID:[New species of yeast from soil--Candida podzolica sp. n]. 122 47


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