Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

D-beta-Hydroxybutyrate dehydrogenase is a lipid-requiring enzyme, which is a tetramer both in the mitochondrial inner membrane and as the purified enzyme reconstituted with phospholipid. For the active enzyme-phospholipid complex in the absence of ligands, we previously found that reaction with N-ethylmaleimide (at 5 mol/mol of enzyme subunit) resulted in progressive loss of enzymic activity with an inactivation stoichiometry of 1 equiv of sulfhydryl derivatized per mole of enzyme and a maximum derivatization of 2 equiv [Latruffe, N., Brenner, S. C., & Fleischer, S. (1980) Biochemistry 19, 5285-5290]. We now find, in the presence of nucleotide or substrate, that the rate of inactivation is significantly reduced, which indicates that these ligands afford protection of the essential sulfhydryl. Further, in the presence of ligands, the inactivation stoichiometry is 0.5, consistent with half-of-the-site reactivity of the essential sulfhydryl. Thus, at a low ratio of N-ethylmaleimide to enzyme, nucleotide or substrate affords essentially complete protection of the nonessential sulfhydryl from derivatization. The binding characteristics of NADH to both the native and N-ethylmaleimide-derivatized enzyme have been compared by fluorescence spectroscopy. Quenching of intrinsic tryptophan fluorescence of the protein shows that the enzyme, derivatized with N-ethylmaleimide either in the absence or in the presence of NAD+, binds NADH but with a reduced Kd (approximately 50 microM as compared with approximately 20 microM for native enzyme). However, a critical change has occurred in that resonance energy transfer from protein to bound NADH, observed in the native enzyme, is abolished in the N-ethylmaleimide-derivatized enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Half-site reactivity of an essential thiol group of D-beta-hydroxybutyrate dehydrogenase. 650 17

A transmembrane electron transport system has been studied in HeLa cells using an external impermeable oxidant, ferricyanide. Reduction of ferricyanide by HeLa cells shows biphasic kinetics with a rate up to 500 nmoles/min/g w.w. (wet weight) for the fast phase and half of this rate for the slow phase. The apparent Km is 0.125 mM for the fast rate and 0.24 mM for the slow rate. The rate of reduction is proportional to cell concentration. Inhibition of the rate by glycolysis inhibitors indicates the reduction is dependent on glycolysis, which contributes the cytoplasmic electron donor NADH. Ferricyanide reduction is shown to take place on the outside of cells for it is affected by external pH and agents which react with the external surface. Ferricyanide reduction is accompanied by proton release from the cells. For each mole of ferricyanide reduced, 2.3 moles of protons are released. It is, therefore, concluded that a transmembrane redox system in HeLa cells is coupled to proton gradient generation across the membrane. We propose that this redox system may be an energy source for control of membrane function in HeLa cells. The promotion of cell growth by ferricyanide (0.33-0.1 mM), which can partially replace serum as a growth factor, strongly supports this hypothesis.
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PMID:Properties of a transplasma membrane electron transport system in HeLa cells. 653 37

We have examined the interaction of hepatic phenylalanine hydroxylase with the phenylalanine analogs, tryptophan and the diastereomers of 3-phenylserine (beta-hydroxyphenylalanine). Both isomers of phenylserine are substrates for native phenylalanine hydroxylase at pH 6.8 and 25 degrees C, when activity is measured with the use of the dihydropteridine reductase assay coupled with NADH in the presence of the synthetic cofactor, 6-methyl-5,6,7,8-tetrahydropterin. However, while erythro-phenylserine exhibits simple Michaelis-Menten kinetics (Km = 1.2 mM, Vmax = 1.2 mumol/min X min) under these conditions, the threo isomer exhibits strong positive cooperativity (S0.5 = 4.8 mM Vmax = 1.4 mumol/min X mg, nH = 3). Tryptophan also exhibits cooperativity under these conditions (S0.5 = 5 mM, Vmax = 1 mumol/min X mg, nH = 3). The presence of 1 mM lysolecithin results in a hyperbolic response of phenylalanine hydroxylase to tryptophan (Km = 4 mM, Vmax = 1 mumol/min X mg) and threo-phenylserine (Km = 2 mM, Vmax = 1.4 mumol/min X mg). erythro-Phenylserine is a substrate for native phenylalanine hydroxylase in the presence of the natural cofactor, L-erythro-tetrahydrobiopterin (BH4) (Km = 2 mM, Vmax 0.05 mumol/min X mg, nH = 2). Preincubation of phenylalanine hydroxylase with erythro-phenylserine results in a 26-fold increase in activity upon subsequent assay with BH4 and erythro-phenylserine, and hyperbolic kinetic plots are observed. In contrast, both threo-phenylserine and tryptophan exhibit negligible activity in the presence of BH4 unless the enzyme has been activated. The product of the reaction of phenylalanine hydroxylase with either isomer of phenylserine was identified as the corresponding p-hydroxyphenylserine by reaction with sodium periodate and nitrosonaphthol. With erythro-phenylserine, the hydroxylation reaction is tightly coupled (i.e. 1 mol of hydroxyphenylserine is formed for every mole of tetrahydropterin cofactor consumed), while with threo-phenylserine and tryptophan the reaction is largely uncoupled (i.e. more cofactor consumed than product formed). Erythro-phenylserine is a good activator, when preincubated with phenylalanine hydroxylase (A0.5 = 0.2 mM), with a potency about one-third that of phenylalanine (A0.5 = 0.06 mM), while threo-phenylserine (A0.5 = 6 mM) and tryptophan (A0.5 approximately 10 mM) are very poor activators. Addition of 4 mM tryptophan or threo-phenylserine or 0.2 mM erythro-phenylserine to assay mixtures containing BH4 and phenylalanine results in a dramatic increase in the hydroxylation at low concentrations of phenylalanine.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The interaction of aromatic amino acids with rat liver phenylalanine hydroxylase. 670 37

When isolated rat pancreatic islets are exposed to L-leucine (20 mM), the rate of NH4 production is close to the summed rates of L-[1-14C] leucine decarboxylation and alpha-ketoisocarproate production, whereas the rates of acetoacetate production and L-[U-14C]-leucine oxidation are compatible with conversion of each mole of the amino acid to one mole of acetoacetate and three moles of CO2. ATP content, ATP/ADP ratio, and adenylate charge are maintained at normal values by L-leucine, whereas the NADH/NAD+ ratio (but not the NADPH/NADP+ ratio) is significantly increased. The release of insulin evoked by L-leucine is potentiated by 2-ketoisovalerate, unaffected by L-valine, and inhibited by menadione. L-leucine mimicks the effect of D-glucose on 86Rb+ and 45Ca2+ handling by the islets. However, relative to its rate of oxidation, the insulinotropic effect of L-leucine is less marked than that of D-glucose. This may be due, in part at least, to a decrease in the oxidation of endogenous nutrients. It is concluded that the metabolic, cationic, and secretory effects of L-leucine in isolated islets are not incompatible with the fuel hypothesis for insulin release.
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PMID:The stimulus-secretion coupling of amino acid-induced insulin release: metabolism and cationic effects of leucine. 676 28

The 7 alpha-dehydroxylation of primary bile acids by Eubacterium sp. V.P.I. 12708 required a cell extract prepared from a cholic acid-induced culture and NAD+. NADH (0.5 mM) inhibited bile acid 7-dehydroxylase activity more than 50% when added to reaction mixtures containing NAD+ (0.5 mM). Saturation kinetics and double reciprocal plots of NADH inhibition were consistent with negative cooperativity. 7-Dehydroxylase activity was modulated by the molar ratio of NAD+-NADH with maximal activity at a NAD+ mole fraction of 0.75 to 0.85. NADH stimulated 7-dehydroxylase activity (30% to 50%) at low concentration (less than 0.15 mM) and inhibited at higher concentrations. Reduction of the proposed delta 6-intermediate (3 alpha-hydroxy-5 beta-6-cholen-24-oic acid) to lithocholic acid required a cell extract from a cholic acid-induced culture and was stimulated by the addition of NAD+. Reduced flavin nucleotides stimulated (32% to 62%) and NADH (0.5 mM) inhibited (78%) the reduction of the delta 6-intermediate to lithocholic acid. 7-Dehydroxylase was highly specific for bile acid substrates and required a free C-24 carboxyl group and an unhindered 7 alpha- or 7 beta-hydroxy group on the B-ring of the steroid nucleus for activity. Bile acid 7 alpha- and 7 beta-dehydroxylase and delta 6-reductase activities all co-eluted from an anaerobic high performance liquid chromatography gel filtration column. However, approximately 80% to 96% of the total units of activity were lost. A substantial portion (20% to 30%) of the total activity was recovered when material from low molecular weight (8,000 to 14,000 Mr) eluting fractions was added back to fractions containing enzyme activity. These studies show that 7-dehydroxylase is highly specific for substrates and its activity may be regulated by the NAD+-NADH ratio in the bacterial cell.
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PMID:Regulation of bile acid 7-dehydroxylase activity by NAD+ and NADH in cell extracts of Eubacterium species V.P.I. 12708. 683 78

Alloxan behaves as a substrate for NADH:ferricytochrome b5 oxidoreductase (EC 1.6.2.2). The apparent Km for alloxan was 10 mM in liver microsomes and 20 mM with the enzyme prepared by lysosomal digestion. The apparent Km for NADH was the same with microsomes and the isolated enzyme (30 microM). The maximum turnover rate was calculated as 426 moles electrons/min X mole enzyme. Cytochrome b5 was shown to reduce alloxan nonenzymatically.
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PMID:Reduction of alloxan by microsomal electron transport proteins. 688 44

The respiratory chain-linked external NADH dehydrogenase has been isolated from Candida utilis in highly purified form. The enzyme is soluble and has a molecular weight of approx. 1.5 x 10(6). The enzyme contains two moles of FMN per mole of enzyme and is composed of two large subunits of mol. wt. 270 000 and eight smaller subunits of mol. wt. 135 000. Iron and copper are present in the preparations, but appear to be contaminants. The enzyme catalyzes the oxidation of NADH and NADPH at nearly equal rates and reacts readily with 2,6-dichlorophenolindophenol, CoQ6 and CoQ1 derivatives as acceptors. Rotenone (10(-5) M) and seconal (10(-3) M) do not inhibit enzymatic activity.
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PMID:Electron transport systems of Candida utilis: purification and properties of the respiratory chain-linked external NADH dehydrogenase. 719 Apr 38

A variety of species of GPDH undergo acylation at two of the four active cystein sites per mole of tetrameric enzyme. This reaction requires tightly bound NAD+, a situation restricted to two of the four NAD sites per tetramer. S leads to N acyl transfer from cysteins to lysine in the diacyl enzyme yields an inactive enzyme. The thiol ester bond of acyl enzyme is activated by NAD+ and NADH for the group transfer and reduction reactions, respectively. In furyl acryloyl-GPDH this activation is accompanied by large acyl-spectral shifts, a "blue shift" with NADH and a "red shift" with NAD+. The group transfer reaction as well as spectral shifts show biphasic kinetics. The amplitude of the fast phase of NAD+-induced spectral change in apo-enzyme is equal to that of the fast phase in phosphorolysis (or arsenolysis) at low [NAD+]. The kinetic pattern of spectral shifts by NAD+ and NADH are complementary; the amplitude of the fast phase in one is equal to that of the slow phase in the other. It has been proposed that the acyl enzyme exists in two conformational states. The relative proportion of these states varies with the extent of covalent (acyl group) or non-covalent (NAD+ or NADH) ligation in a manner consistent with the allosteric model of Monod, Wyman and Changeux. These conclusions apply equally to the true substrate acyl enzyme. With 1,3-diphosphoglycerate, a tetra-acylated enzyme is obtained. Two of these four acyl groups react very much faster than the remaining two. A comparison of their specific rates with the steady state turnover numbers indicates that only the less reactive two acyl groups govern the turnover number of the enzyme.
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PMID:Structural and functional consequences of subunit interactions in glyceraldehyde 3-phosphate dehydrogenase. 722 60

The interaction of xanthomegnin, a quinone pigment, with the mitochondrial respiratory chain was demonstrated. Xanthomegnin was reduced by succinate, in the presence of submitochondrial particles or mitochondria, only after all oxygen had been consumed in the system, and the reduction was inhibited by antimycin A or KCN. Xanthomegnin was immediately reduced by NADH in a similar system, the reduced xanthomegnin was reoxidized by oxygen but the reduction by NADH was not inhibited by antimycin A or KCN. Xanthomegnin was also immediately reduced by NADH catalyzed by a purified particulate NADH dehydrogenase complex showing a molar ratio of 2 moles NADH for one mole of xanthomegnin. Reoxidation of the reduced pigment by oxygen occurred in this system. Oxygen consumption was accelerated when xanthomegnin was added to a reaction medium containing NADH, NADH segment and cytochrome c oxidase. Subsequent addition of cytochrome c resulted in a further marked acceleration of oxygen consumption. These results suggest that xanthomegnin interacts with the NAD-linked respiratory chain to produce a xanthomegnin shunt, but this does not occur with the succinate-linked chain.
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PMID:The interaction of a quinone pigment, xanthomegnin, with the mitochondrial respiratory chain. 726 94

The activity of the pI 5 isozyme of horse liver aldehyde dehydrogenase is markedly enhanced by some divalent metal ions (Ca, Mn, Mg), inhibited by others (Fe, Cu, Cd), totally inhibited by Hg, and not significantly affected by still others (Zn, Ni, Co). Steady-state kinetics show that with 0.5 mM Mg or Mn a 2-fold activation of the velocity measured at pH 7.5 occurs when propionaldehyde is the substrate. In the pre-steady state, the magnitude burst of NADH formulation is increased from 2 moles formed per mole of tetrameric enzyme to 4 moles formed in the presence of Mg. The stoichiometry of coenzyme (NADH, NAD, epsilon-NAD) binding is also increased from essentially 2 moles binding to 4 moles binding per mole enzyme in the presence of Mg. It appears that the enzyme exhibits half of the site reactivity in the absence of metal but has a full complement of catalytic sites in the presence.
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PMID:Mechanism of the magnesium ion activation of the catalytic activity of horse liver aldehyde dehydrogenase. 742 5


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