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)

A new method for the determination of guanase is described. Xanthine, the product of the guanase reaction, is oxidized by xanthine oxidase, forming uric acid and hydrogen peroxide. Hydrogen peroxide is further reduced to water by catalase in the presence of ethanol. The acetaldehyde formed in this reaction step is dehydrogenated NAD or NADP dependent by aldehyde dehydrogenase. The NADH or NADPH production is measured and utilized for the calculation of the guanase activity. The sensitivity of the method can be doubled by the addition of uricase, which oxidizes uric acid to permit the formation of another mole of hydrogen peroxide.
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PMID:A new spectrophotometric assay for enzymes of purine metabolism. II. Determination of guanase activity. 48 57

Incubation of horse liver aldehyde dehydrogenase (aldehyde:NAD oxidoreductase, EC 1.2.1.3) with 2-hydroxyethyl disulfide formed mixed-disulfides between protein sulfhydryl groups and beta-mercaptoethanol. Reduction of aldehyde dehydrogenase activity may be associated with formation of one, or at most two, mixed-disulfides per dehydrogenase subunit. Characteristically in the case of a mixed-disulfide, inactivation was was reversed by addition of thiols. Other disulfides also inactivated aldehyde dehydrogenase. The pseudo first-order rate constants for the forward and reverse reactions (aldehyde dehydrogenase + 2-hydroxyethyl disulfide in equilibrium or formed from modified aldehyde dehydrogenase + beta-mercaptoethanol) were 0.70 and 2 liter mole-1 sec-1, respectively. The equilibrium constant was approximately 0.4. After extended incubation under conditions expected to result in complete modification of aldehyde dehydrogenase, 30% of the initial catalytic activity remained. This suggests that 2-hydroxyethyl disulfide-treated aldehyde dehydrogenase retains catalytic activity and that the sulfhydryl group modified by 2-hydroxyethyl disulfide is not essential for aldehyde dehydrogenase activity.
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PMID:Reversible inactivation of horse liver aldehyde dehydrogenase by 2-hydroxyethyl disulfide. 726 35

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

10-Formyltetrahydrofolate dehydrogenase (EC 1.5.1.6) was previously identified as a folate-binding protein in rat liver cytosol (R.J. Cook and C. Wagner, Biochemistry 21, 4427-4434, 1982) by virtue of the tetrahydrofolate polyglutamate tightly bound to the partially purified enzyme. In this current study we provide evidence to show that when liver cytosol was rapidly processed to identify the protein bound folate, large amounts of both 10-formyl- and 5-formyltetrahydrofolate were present. After overnight storage of the cytosol at 5 degrees C before processing, almost no formylfolates were present and the major protein-bound form was tetrahydrofolate. This suggests that 10-formyltetrahydrofolate polyglutamates are tightly bound to the enzyme in vivo and are converted to tetrahydrofolate forms during isolation by the hydrolase activity associated with the enzyme. Covalent binding of the stable folate analogue, 5-formyltetrahydrofolate, to the purified enzyme resulted in 2 mol bound per mole of enzyme subunit. This is consistent with earlier reports suggesting the enzyme is capable of carrying out both oxidative and hydrolytic conversion of 10-formyltetrahydrofolate to tetrahydrofolate at the same time. Partial tryptic digestion of the purified enzyme selectively inhibited dehydrogenase activity of the enzyme but did not affect the hydrolase or aldehyde dehydrogenase activities.
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PMID:10-Formyltetrahydrofolate dehydrogenase: identification of the natural folate ligand, covalent labeling, and partial tryptic digestion. 784 Jun 9

Isoflavonoid derivatives including prunetin (4',5-dihydroxy-7-methoxyisoflavone) were shown to be potent inhibitors of human aldehyde dehydrogenases (Keung W-M and Vallee BL, Proc Natl Acad Sci USA 90: 1247-1251, 1993). The inhibition reaction was reinvestigated using recombinantly expressed human aldehyde dehydrogenases. The kinetic analyses showed that prunetin inhibits competitively against both NAD and propionaldehyde with the mitochondrial and cytoplasmic enzymes. The Ki value for the mitochondrial enzyme was much lower than for the cytoplasmicenzyme. A mixed pattern of inhibition was obtaiend with the mitochondrial enzyme in the presence of Mg2+. Only one mole of prunetin binds per mole of tetrameric mitochondrial enzyme, which remains unaltered in the presence of Mg2+. Prunetin did not displace NADH from the enzyme-NADH complex. Propionaldehyde did not reverse the loss of fluorescence obtained due to enzyme-prunetin complex formation, indicating that prunetin may not be interacting at the substrate site. The esterase activity of the mitochondrial enzyme was also inhibited by prunetin in a competitive manner. The replacement of lysine 192 by glutamine resulted in a mutant with a 20% kcat and a 100-fold increase in the Km for NAI) compared with the native enzyme. However, the Ki value of prunetin against NAD was similar to that observed with the native enzyme. Prunetin, even at a very high concentration, was not an inhibitor of alcohol and malate dehydrogenase. It was concluded that prunetin may act as an allosteric inhibitor of aldehyde dehydrogenase.
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PMID:Allosteric inhibition of human liver aldehyde dehydrogenase by the isoflavone prunetin. 910 97

Human liver mitochondrial aldehyde dehydrogenase is a tetrameric enzyme composed of 4 identical 500 amino acid containing subunits arranged such that the protein is a dimer of dimers. No kinetic evidence for subunit interactions has been reported. However, the enzyme exhibits half-of-the-site reactivity in that there is a pre-steady-state burst of 2 mol of NADH per mole of enzyme. A variant of the enzyme, found in Asian people, contains a lysine rather than a glutamate at position 487. This enzyme has a high K(M) for NAD(+) and a low specific activity. In heterotetramers composed of both subunit types, it appeared that the lysine-containing subunit was dominant over the glutamate-containing subunits. To allow for the separation of various heterotetrameric forms of the enzyme, surface residues were changed. Each of the five possible tetrameric forms of the modified enzyme was isolated and characterized with respect to steady-state kinetics and pre-steady-state burst magnitudes. The data best fit a model where in each dimer pair there is one functioning and one nonfunctioning subunit. Further, the lysine subunit affects the properties only of its dimer partner. Residue 487 is located at the dimer interface, and the glutamate forms salt bonds with two arginine residues. One is to Arg(264) in the same subunit; the other is to Arg(475) located in the other subunit. Most likely the presence of a lysine affects these salt bonds so the lysine subunit can cause the other subunit to become essentially nonfunctional.
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PMID:Basis for half-of-the-site reactivity and the dominance of the K487 oriental subunit over the E487 subunit in heterotetrameric human liver mitochondrial aldehyde dehydrogenase. 1100 16