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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Induced wildtype cells of A. nidulans rapidly lost NADPH--linked nitrate reductase activity when subjected to carbon and or nitrogen starvation. A constitutive mutant at the regulatory gene for nitrate reductase, nir Ac 1, rapidly lost nitrate reductase activity upon carbon starvation. This loss of activity is thought to be due to a decrease in the NADPH concentration in the cells. Cell free extracts from wildtype cells grown in the presence of nitrate, rapidly lost their nitrate reductase activity when incubated at 25 degrees C. NADPH prevented this loss of activity. Wildtype cells grown in the presence of nitrate and urea have a higher initial NADPH:NADP+ ratio and cell free extracts from such cells lost their nitrate reductase activity slower than extracts of cells grown with nitrate alone. The Pentose Phosphate Pathway mutant, pppB-1, had a lower NADPH concentration compared with the wildtype grown under the same conditions and cell free extracts lost their nitrate reductase activity more rapidly than the wildtype. Cell free extracts of nirAc-1 and a non-inducible mutant for nitrate reductase, nirA- -14, upon incubation lost little of their nitrate reductase activity.
Mol Gen Genet 1977 Apr 29
PMID:In vivo and in vitro studies of nitrate reductase regulation in Asperillus nidulans. 1 26

The lower Vmax of 6PGDH with respect to G6PDH and its higher sensitivity to inhibition by NADPH, suggest the existence of an imbalance between the two dehydrogenases of the pentose phosphate pathway in rat liver. Possible modulators of these activities, particularly in relation with the inhibition by NADPH in physiological conditions, have been investigated. The results suggest that in both cases the inhibition by NADPH is strictly isosteric and that the relative affinities for the reduced and oxidized forms of the pyridine nucleotide are unaffected by glutathion, the intermediates of the pentose phosphate shunt or some divalent ions.
Mol Cell Biochem 1977 Oct 07
PMID:Effectors of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase of rat liver. 2 33

We have studied the isocitrate dehydrogenase of Tetrahymena pyriformis. This enzyme is able to utilize both NAD and NADP, but kinetic studies suggest that the enzymatic activity with NAD is not of physiological signifance. Some of the factors that might regualte the NADP-dependent isocitrate dehydrogenase were also studied. This enzyme has an absolute requirement for divalent cations; Mg,+ and Mn2+ will serve as cofactors but the latter is more effective than the former. It is known that this enzyme is subject to a concerted inhibition by oxaloacetate and glyoxylate. Either glyoxylate or oxaloacetate alone also are capable of inhibiting the enzyme although higher concentrations are required. We have found concerted inhibition also for the NAD-dependent isocitrate dehydrogenase from rat liver and yeast. The activity of the Tetrahymena pyriformis enzyme is inhibited by NADPH. This inhibition is competitive with NADP. The Ki and Km values are, respectively, 20 micrometers and 18 micrometers.
Mol Cell Biochem 1977 Oct 07
PMID:Isocitrate dehydrogenase of Tetrahymena pyriformis. 2 34

NADP+-dependent cytoplasmic malic enzyme was purified to homogeneity from mouse kidneys by a two-step procedure involving 8-(6-aminohexyl)-amino-2', 5'-ADP-Sepharose affinity chromatography and DEAE-Sephadex ion exchange chromatography. The biochemical properties of the purified enzyme from DBA/2J mice were characterized. These include the determination of molecular weight and amino acid compositions, steady-state kinetics, thermal stability and inactivations by iodoacetate and urea. The native enzyme is a tetramer with a molecular weight of 270,000.Km's for NADP+, L-malate, NADPH and pyruvate were determined to be 3.3 micrometer, 50 micrometer, 10.5 micrometer respectively. Similar to the pigeon liver enzyme, the mouse enzyme exhibits an ordered kinetic mechanism proceeding with the binding of coenzyme first. The enzyme is only weakly inhibited by ATP and other cellular metabolites. A remarkable similarity in amino acid compositions was found between the mouse and rat liver malic enzymes.
Mol Cell Biochem 1978 Nov 30
PMID:Cytoplasmic malic enzyme from mouse kidneys. 3 24

The oxidative response to phagocytosis by chicken polymorphonuclear leucocytes was investigated as compared to guinea pig polymorphonuclear leucocytes. The polymorphs from both species respond to phagocytosis with an increased oxygen consumption, an increased generation of O2 and H2O2, and an increased oxidation of glucose through the hexose monophosphate shunt. The rate of oxygen consumption, and generation of O2- and H2O2 by phagocytosing chicken polymorphonuclear leucocytes is considerably lower than with phagocytosing guinea pig polymorphonuclear leucocytes. By contrast, the extent of hexose monophosphate shunt stimulation in chicken polymorphs is comparable to that of guinea pig polymorphs. Evidence is presented suggesting that H2O2 is preferentially degraded in chicken cells through the glutathione cycle, whereas catalase and myeloperoxidase are the two main H2O2 degrading enzymes in guinea pig cells. The 20,000 g fraction of the postnuclear supernatant of chicken polymorphs contains a cyanide-insensitive NADPH oxidizing activity which is stimulated during phagocytosis. Similar properties for the NADPH oxidizing activity of guinea pig polymorphs have been previously reported. It is concluded that the metabolic burst of phagocytosing chicken polymorphonuclear leucocytes is qualitatively similar to that of guinea pig polymorphonuclear leucocytes, but the latter cells are more active in all the biochemical parameters that have been measured. The difference in the H2O2 degradation pathways between the two species is accounted for by the lack of myeloperoxidase and catalase in chicken polymorphs.
Mol Cell Biochem 1978 Dec 22
PMID:Oxidative metabolism of chicken polymorphonuclear leucocytes during phagocytosis. 3 93

In the first part of the review the background to the discovery of the asymmetric synthesis of squalene from two molecules of farnesyl pyrophosphate and NADPH is described, then the stereochemistry of the overall reaction is summarized. The complexity of the biosynthesis of squalene by microsomal squalene synthetase demanded the existence of some intermediate(s) between farnesyl pyrophosphate and squalene. This demand was satisfied by the discovery of presqualene pyrophosphate, an optically active C30 substituted cyclopropylcarbinyl pyrophosphate, the absolute configuration of which at all three asymmetric centers of the cyclopropane ring was deduced to be R. Possible mechanisms for the biosynthesis of presqualene pyrophosphate and its reductive transformation into squalene are presented. In the second part of the review the nature of the enzyme is discussed. The question whether presqualene pyrophosphate is an obligate intermediate in the biosynthesis of squalene is examined, with the firm conclusion that it is. It is as yet uncertain whether the two half reactions of squalene synthesis, i.e. (i) 2 x farnesyl pyrophosphate leads to presqualene pyrophosphate; (ii) presqualene pyrophosphate + NADPH (NADH) leads to squalene, are catalyzed by one or two enzymes or by a large complex with two catalytic sites. Evidence is cited for the existence on the enzyme of two distinct binding sites with different affinities for the two farnesyl pyrophosphate molecules. The types of enzyme preparations available at present are described and types of experiments carried out with these are critically examined. The implications of the properties of a low molecular weight squalene synthetase solubilized with deoxycholate from microsomal membranes is discussed and a model for the enzyme in an organized membrane structure is presented.
Mol Cell Biochem 1979 Oct 15
PMID:Squalene synthetase. 4 Nov 73

The amino acid compositions of several monomeric NADPH-dependent aldehyde reductases from a variety of species have been determined and analyzed by the difference index method of Metzger et al. (1968). The difference indexes among mammals range from 4.15 - 6.10 indicating considerable homology. Comparison of chicken aldehyde reductase with mammalian aldehyde reductases gave values in the range 6.8 - 9.9 suggesting a close relationship whereas the difference indexes for the enzymes from fruit fly and Baker's yeast versus vertebrate aldehyde reductases (10.9 - 14.4) indicate more distant relationships. The extent of sequence homology among aldehyde reductases from these species was estimated from a plot of difference index versus percent sequence difference for oxido-reductases of known sequence. From this plot, and using a mammal-chicken divergence time of 300 million years and a mammalian order split of 75 million years, the rate of evolution of aldehyde reductases was calculated to lie in the range 5.8 - 15.6% sequence difference per 100 million years. Comparison with rates of evolution of oligomeric dehydrogenases indicates that aldehyde reductases comprise the most rapidly evolving family of oxido-reductases. This is probably related to the monomericity of aldehyde reductases since there is a direct correlation between the number of subunits and the rate of evolution.
J Mol Evol 1979 Dec
PMID:Compositional relatedness of aldehyde reductases from several species. 4 5

NAD(P)H: FMN oxidoreductase (flavin reductase) couples in vitro to bacterial luciferase. This reductase, which is also postulated to supply reduced flavin mononucleotide in vivo as a substrate for the bioluminescent reaction, has been partially purified and characterized from two species of luminous bacterial. From Photobacterium fischeri the enzyme has a M. W. determined by Sephadex gel filtration, of 43,000 and may have a subunit structure. The turnover number at 20 degrees C, based on a purity estimate of 20 percent, is 1.7 times 10-4 moles of NADH oxidized per min per mole of reductase. The reductase isolated from Beneckea harveyi has an apparent molecular weight of 23,000; its purity was too low to permit estimation of specific activity. Using a spectrophotometric assay at 340 nm with the P. fischeri reductase, both NADH (Km, 8 times 10-5 M) and NADPH (Km, 4 times 10-4 M) were enzymatically oxidized, the Vmax with NADH being approximately twice that of NADPH. Of the flavins tested in this assay, only FMN (Km, 7.3 times 10-5 M) and FAD (Km, 1.4 times 10-4 M) were effective, FMN having a Vmax three times that of FAD. In the coupled assay, i.e., measuring the bioluminescence intensity of the reaction with added luciferase, the optimum FMN concentration was nearly 100 times less than in the spectrophotometric assay. The studies reported suggest the existence of a functional reductase-luciferase complex.
Mol Cell Biochem 1975 Jan 31
PMID:Flavin mononucleotide reductase of luminous bacteria. 4 4

Rat kidney microsomes have been found to catalyze the hydroxylation of medium-chained fatty acids to the omega- and (omego-1)-hydroxy derivatives. This reaction, which requires NADPH and molecular oxygen, is a function of monooxygenase system present in the kidney microsomes, containing NADPH-cytochrome c reductase and cytochrome P-450K. NADH is about half as effective as an electron donor as NADPH and there is an additive effect in the presence of both nucleotides. Cytochrome P-450K absorbs light maximally at 452-3 nm, when it is reduced and bound to carbon monoxide. The extinction coefficient of this complex is 91 mM(-1) cm(-1). Electrons from NADPH are transferred to cytochrome P-450K via the NADPH-cytochrome c reductase. The reduction rate of cytochrome P-450K is stimulated by added fatty acids and the reduction kinetics reveal the presence of endogenous substrates bound to cytochrome P-450K. Both cytochrome P-450K concentration and fatty acid hydroxylation activity in kidney microsomes are increased by starvation. On the other hand, phenobarbital treatment of the rats has no effect on either the hemoprotein or the overall hydroxylation reaction and 3,4-benzpyrene administration induces a new species of cytochrome P-450K not involved in fatty acid hydroxylation. Cytochrome P-450K shows, in contrast to liver P-450, high substrate specificity. The only substances forming enzyme-substrate complexes with cytochrome P-450K are the medium-chained fatty acids and certain derivatives of these acids. The chemical requirements for substrate binding include a carbon chain of medium length and at the end of the chain a carbonyl group and a free electron pair on a neighbouring atom. The distance between the binding site for the carbonyl group and the active oxygen is suggested to be in the order of 16 A. This distance fixes the ratio of omega- and (omega-1)-hydroxylated products formed from a certain fatty acid by the single species of cytochrome P-450K involved. The membrane microenvironment seems also to be of importance for the substrate specificity of cytochrome P-450K, since removal of the cytochrome from the membrane lowers its binding specificity to some extent. A comparison between the liver and kidney cytochrome P-450 systems suggests that the kidney cytochrome P-450K system is specialized for fatty acid hydroxylation.
Mol Cell Biochem 1975 Aug 30
PMID:Fatty acid hydroxylation in rat kidney cortex microsomes. 24 Oct 11

In Saccharomyces cerevisiae, a small proportion of the glucose-6-P dehydrogenase activity is firmly associated with the mitochondrial fraction and is not removed by repeated washing or density-gradient centrifugation. However, the enzyme is released by sonic disruption. Mitochondrial glucose-6-P dehydrogenase that is released by sonication and partially purified has been found to be similar to cytosol glucose-6-P dehydrogenase with respect to electrophoretic mobility, isoelectric point, pH optimum, molecular size, and apparent KM's for NADP+ and glucose-6-P. These results indicate that a single species of glucose-6-P dehydrogenase is synthesized in S. cerevisiae and that the enzyme has more than one intracellular location. Mitochondrial glucose-6-P dehydrogenase may be a source of intramitochondrial NADPH and may function with hexokinase and transhydrogenase to provide a pathway for glucose oxidation that is coupled to the synthesis of mitochondrial ATP. A constant proportion of total glucose-6-P dehydrogenase activity remains compartmented in the mitochondrial fraction throughout the growth cycle.
Mol Cell Biochem 1979 May 06
PMID:Mitochondrial glucose-6-phosphate dehydrogenase from Saccharomyces cerevisiae. 38 93


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