pCytoplasmic aldehyde dehydrogenase catalyses the hydrolysis of methyl p-nitrophenyl (PNP) carbonate at an appreciable rate that is markedly stimualted by NAD+ or NADH. The nuleotides accelerate the rate-limiting hydrolysis of the acyl-enzyme intermediate while slowing the observed burst of p-nitrophenoxide production. With PNP dimethylcarbamate the enzyme catalyses the slow release of approx. 1 molecule of p-nitrophenoxide per tetrameric enzyme molecule; during the reaction the enzyme becomes effectively inactivated, as the rate of hydrolysis of the acyl-enzyme is virtually zero. The presence of NAD+, NADH, propionaldehyde, chloral hydrate, diethylstilboestrol or disulfiram slows the reaction of enzyme with PNP dimethylcarbamate. The reaction appears to be dependent on a group of pKa 7.6, possibly a cysteine residue. The effect of PNP dimethylcarbamate on the dehydrogenase activity of the enzyme is consistent with there being a single type of active site for the enzyme9s dehydrogenase and esterase activities. Steric and electronic factors that govern reaction of the enzyme with PNP substrates are discussed./p
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机译:细胞质醛脱氢酶以明显的速率催化碳酸甲基对硝基苯基酯(PNP)的水解,该速率明显受到NAD +或NADH的刺激。核苷酸加速了酰基酶中间体的限速水解,同时减慢了对硝基苯酚生成的爆发。使用PNP二甲基氨基甲酸酯时,该酶可催化约5%的缓慢释放。每个四聚体酶分子1个对硝基苯酚分子;在反应过程中,由于酰基酶的水解速率实际上为零,因此该酶被有效地灭活。 NAD +,NADH,丙醛,水合氯醛,二乙基雌二醇或双硫仑的存在会减慢酶与PNP二甲基氨基甲酸酯的反应。该反应似乎取决于一组pKa 7.6,可能是一个半胱氨酸残基。 PNP二甲基氨基甲酸酯对酶的脱氢酶活性的影响与酶的脱氢酶和酯酶活性存在单一类型的活性位点是一致的。讨论了控制酶与PNP底物反应的立体和电子因素。 p>
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