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

Intact cells obtained from Mycobacterium scrofulaceum as well as from mycobacterial strains M.A6 and M.R56 isolated respectively from leprous tissues of armadillo and rat leproma and grown with glycerol as the oxidizable substrate catalyzed complete oxidation of formate. The stoichiometry of formate oxidase system yielded a value of 2 mol of CO2 produced per mole of O2 or per 2 moles of formate consumed. Cell-free preparations from these three strains of mycobacteria contained formate dehydrogenase which was associated exclusively in the particulate fraction. Formate oxidation was markedly stimulated by small amounts of selenite and molybdate added together. Formate-reduced minus oxidized difference spectra disclosed cytochromes of the b type while spectral evidence did not suggest the existence of cytochromes a or c components. The effect of 2-N-heptyl-4-hydroxyquinoline-N-oxide on the redox state of cytochromes indicated that formate oxidation was mediated by cytochrome b with absorption maximum of 556 nm and not of 562 nm.
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PMID:Oxidation of formate by mycobacteria of the scrofulaceum group. 74 15

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

Nitric oxide reductase was purified from Paracoccus denitrificans very nearly to homogeneity by a simple method that involved the use of octyl glucoside to solubilize the enzyme from membranes and required a single hydroxyapatite column. The enzyme had specific activities of about 10 mumol NO reduced x min-1 x mg-1 at pH 6.5 in an amperometric assay system using phenazine methosulfate/ascorbate as the reducing agent and about 22 mumol NO reduced x min-1 x mg-1 at pH 5.0, which is the optimum pH. These values are based on average rates over kinetically complex progress curves and would be about three times greater if based on maximum rate values. The enzyme appeared to be reversibly inhibited by NOaq and to have a Km too low (probably less than or equal to 1 microM) to measure reliably by the amperometric method. The effective second-order rate constant of the enzyme lay within 1 to 2 orders of magnitude of the diffusion controlled limit. The enzyme was composed of a tight complex of two cytochromes: a cytochrome c (Mr = 17,500) and a cytochrome b (Mr = 38,000). The mole ratios of cytochrome c to cytochrome b and Mr 17,500 peptide to Mr 38,000 peptide were both about 1.7, and the heme content was about 3 mol/73,000 g (38,000 + 2(17,500)). Each subunit therefore contained only one heme group. The Mr 38,000 peptide aggregated when heated in the sample buffer used for sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In addition to the ascorbate-based activity, the enzyme showed a little NADH-NO oxidoreductase activity which was not inhibited by antimycin A. The enzyme lost activity with a half-life of about 2 days at 4 degrees C but could be preserved at -20 degrees C and in liquid nitrogen. It seemed not to be inactivated by aerobic solutions. These observations, and the recent ones by Carr and Ferguson (Carr, G.J., and Ferguson, S.J. (1990) Biochem. J. 269, 423-429) with a partially purified preparation of nitric oxide reductase, establish that the enzyme from Pa. denitrificans is a cytochrome bc complex which resembles that from Pseudomonas stutzeri (Heiss, B., Frunzke, K., and Zumft, W.G. (1989) J. Bacteriol. 171, 3288-3297). There would appear to be no functional relationship between nitric oxide reductase and a Mr = 34,000 peptide of Pa. denitrificans membranes reported previously to be present in purified preparations of a nitric oxide reductase (Hoglen, J., and Hollocher, T.C. (1989) J. Biol. Chem. 264, 7556-7563).
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PMID:Nitric oxide reductase. Purification from Paracoccus denitrificans with use of a single column and some characteristics. 164 15

Two cytochrome b respiratory-deficient mutants were sequenced and their DNA base change identified, leading to the replacement of glycine (G137 by valine or glutamic acid. No variation in their cytochrome b content with regard to cytochrome oxidase and cytochrome (c + c1) was found to have occurred. Their cellular respiratory activity with various substrates was partly conserved and was totally inhibited by antimycin A. Their ubiquinol (QH2)-cytochrome c reductase/mole cytochrome b activity decreased by about 50%. Paradoxically their growth on respiratory substrate was abolished. Both mutants retained a high-affinity binding site for antimycin A, and exhibited a myxothiazol-resistance at the mitochondrial level. It seems likely that the mutated position (137), which belongs to the ubiquinol oxidizing domain of the bc1 complex, interferes, directly or indirectly, with the respiratory growth capacity of the cell.
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PMID:Two substitutions at the same position in the mitochondrial cytochrome b gene of S. cerevisiae induce a mitochondrial myxothiazol resistance and impair the respiratory growth of the mutated strains abbeit maintaining a good electron transfer activity. 207 67

The reactions between cellobiose and cellobiose oxidase were investigated by stopped-flow spectrophotometry. Under anaerobic conditions rapid reduction of the associated flavin is followed by slower reduction of cytochrome b. The kinetic difference spectra are reported. The rate of flavin reduction depends on the cellobiose concentration (with an apparent second-order rate constant of approx. 10(5) M-1.s-1) but reaches a rate limit of approx. 20 s-1. In contrast, the rate of cytochrome b reduction decreases at high cellobiose concentrations. Kinetic titrations of the flavin and cytochrome b moieties yield the stoichiometries of the separate reactions, i.e. the number of moles of cellobiose needed to fully reduce 1 mole of each redox component. The rate constant for cytochrome b reduction, unlike that for flavin reduction, increased with enzyme concentration, prompting the conclusion that any given cytochrome b centre is reduced preferentially by flavin groups in different molecules rather than by its partner flavin within the same monomer. These data are discussed in the context of a scheme that rationalizes them and accounts for the overall stoichiometry in which three two-electron donors (cellobiose molecules) reduce two three-electron acceptors (the flavin-cytochrome b of cellobiose oxidase).
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PMID:Rapid kinetic studies of the reduction of cellobiose oxidase from the white-rot fungus Sporotrichum pulverulentum by cellobiose. 322 48

A new membrane-bound b-type cytochrome, cytochrome b-558, was removed from chromatophore membranes of photosynthetically grown Rhodopseudomonas sphaeroides strain R-26 by deoxycholate-cholate extraction. The cytochrome was purified by ammonium sulfate fractionation and ion-exchange chromatography. Cytochrome b-558 had absorption maxima at 280 and 405 nm in the oxidized form, and at 558, 528, and 420 nm in the reduced form. It had a midpoint potential of--130 mV at pH 7.0. The minimal molecular weight of this protein was 42,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it contained one mole heme per mole of protein. The isoelectric point was 8.5. The electrophoretic pattern of heme-carrying proteins and the redox potentiometry showed that cytochrome b-558 was present in membranes from wild type, strain R-26, and strain GA grown photosynthetically, but not from any strain grown aerobically.
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PMID:A new membrane-bound b-type cytochrome, cytochrome b-558, from photosynthetically grown Rhodopseudomonas sphaeroides. 348 57

1. The cytochrome content of beef liver mitochondria differs from that of beef heart mitochondria by an eightfold lower cytochrome aa3 and a twofold lower cytochrome b and c + c1 content. 2. The kinetic properties of cytochrome c oxidases from beef liver and heart were measured with intact cytochrome c-depleted membranes, deoxycholate-dissolved membranes, and with the isolated enzymes at various cytochrome c concentrations with an oxygen electrode. Under all conditions a higher V was found for the liver enzyme, both for the low-affinity and for the high-affinity binding site for cytochrome c. Differences were also found for the Km of the two enzymes. 3. Isolated beef heart mitochondria contained about twice as much cardiolipin than beef liver mitochondria. The isolated enzymes contained one mole cardiolipin per mole of the heart enzyme, but 2 moles cardiolipin per mole of the liver enzyme. 4. By application of a high performance sodium dodecylsulfate gel electrophoretic system the two isolated enzymes could be separated into 13 different protein components, three of which (polypeptides VIa, VIIa and VIII) were found to differ in their apparent molecular weights. The functional meaning of cytochrome c oxidase isoenzymes in liver and heart is discussed.
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PMID:Kinetic and structural differences between cytochrome c oxidases from beef liver and heart. 628 12

The oxidation of cytochrome b561 by ATP was measured in submitochondrial particles inhibited by antimycin. The redox potential of the bulk (M phase) was controlled by the ratio of fumarate:succinate, and the oxidation of cytochrome b was calculated and expressed as a change in redox potential (Eh) measured in millivolts. The oxidation of cytochrome b561 is an energy-driven reaction affected only by the delta psi component of the proton motive force. The oxidation (measured in millivolts) is a function of the phosphate potential, reaching a maximal value of 40 mV at delta G'ATP less than - 12 kcal/mole. The maximal measured value of ATP-dependent delta psi was 100 mV. Thus only a fraction of the membrane potential effects the redox state of cytochrome b561. In contrast to the ATP-induced oxidation of cytochrome b561, cytochrome b566 is in redox equilibrium with fumarate succinate either in the presence or in the absence of ATP. The selective oxidation of b561 is explained within the term of the Q cycle as a reflection of delta psi on the electron electrochemical potential. The positive electric potential of the C phase causes cytochrome b566 to act as oxidant with respect to cytochrome b561. In the presence of antimycin cytochrome b561 cannot equilibrate with the quinone and undergoes oxidation, while cytochrome b566 reequilibrates with the quinone and thus regains redox equilibrium with the fumarate succinate redox buffer.
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PMID:The effect of membrane potential on the redox state of cytochrome b561 in antimycin-inhibited submitochondrial particles. 726 19

The latent NADPH oxidase activity of purified cytochrome b(558) from rabbit peritoneal neutrophils was expressed in a cell-free system consisting of either gel-filtrated cytosol from resting neutrophils, or a mixture of the three cytosolic activation factors, namely p47, p67 and the G protein Rac1. The cell-free system was supplemented with arachidonic acid and GTPgammaS. With gel-filtrated cytosol, the oxidase activity was relatively high (22 moles O(2)(-)/s/mole heme b in the absence of added FAD), and enhanced by less than one fourth upon addition of FAD. In contrast, with the purified cytosolic activation factors the rate of O(2)(-) production was low (8 moles O(2)(-)/s/mole heme b), and enhanced more than two-fold by a saturating concentration of FAD. The specificity of FAD was demonstrated by the lack of effect of FMN. FAD was determined together with heme b and the oxidase activity in eluates from a Sepharcryl column at the last step of the purification of cytochrome b(558). In the eluted fraction that contained both the maximal inducible oxidase activity and the highest amount of heme b, the molar amount of FAD was 20 times less than that of heme b. It is concluded that cytochrome b(558) is an NADPH-dependent flavocytochrome oxido-reductase (NADPH oxidase) in which one part of FAD is firmly bound and another, loosely attached. On the other hand, there may exist a parallel pathway of electron transfer from NADPH via distinct FAD dehydrogenase(s) to the heme b component of the NADPH oxidase.
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PMID:Assessment of the flavoprotein nature of the redox core of neutrophil NADPH oxidase. 864 81

We describe the molecular evolution of cytochrome b of blind subterranean mole rats. We examined 12 individuals for nucleotide differences in the region of 402 base pairs of mitochondrial cytochrome b. Each individual represents a different population from the entire ecological and speciational range of the four chromosomal species in Israel (2n = 52, 54, 58, and 60) belonging to the Spalax ehrenbergi superspecies. Our results indicate the following. (i) There are seven first-position transitional differences, compared to 34 variable third positions, with no observed second-position substitutions. (ii) A maximum of four amino acids differences occurs across the range. (iii) Within-species diversity increases southward. Only 1 autoapomorphic substitution characterizes either 2n = 52 or 2n = 54, but 6-11 substitutions characterize 2n = 58, and 9-13 substitutions characterize 2n = 60. (iv) Both parsimony and maximum-likelihood trees suggest two monophyletic groups: (a) 2n = 52 and 54, and (b) 2n = 58 and 60, as identified earlier by other protein and DNA markers. (v) Mitochondrial cytochrome b heterogeneity is significantly correlated with climatic factors (rainfall) and biotic factors (body size and allozymes). We hypothesize that two selective regimes direct cytochrome b evolution in the S. ehrenbergi superspecies: (i) purifying selection in the flooded, mesic, hypoxic northern range of 2n = 52 and 54 and (ii) diversifying selection in the climatically spatiotemporal, xeric, and variable southern range of 2n = 58 and 60. Thus, the molecular evolution of mitochondrial cytochrome b in S. ehrenbergi is explicable by opposite selective stresses across the range of S. ehrenbergi in Israel, associated with the ecological adaptive radiation of the complex.
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PMID:Molecular evolution of cytochrome b of subterranean mole rats, Spalax ehrenbergi superspecies, in Israel. 1044 73


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