Mechanism of p - Nitrosophenol Reduction Catalyzed by Horse Liver and Human m - Alcohol Dehydrogenase ( ADH ) HUMAN T -

The mechanism of reduction of p-nitrosophenol (pNSP) catalyzed by horse liver alcohol dehydrogenase (HADH) and human a-alcohol dehydrogenase (a-ADH) has been compared in transient and steady-state experiments. Our results indicate that pNSP reduction catalyzed by these two ADH proceeds by different mechanisms. In one mechanism, shown by Equation 1, pNSP is reduced to p-aminophenol (PAP) via two enzymatic steps (Steps 1 and 3), which are mediated by the nonenzymatic dehydration of p-N-hydroxyaminophenol (pNO W ) to 1,4-benzoquinoneimine (BQI) (Step 2). quent characterization of the NAD(P)H-C-nitroso reductase activity of cytosol from liver and other tissues (2-8) indicated, based on the sensitivity of the reaction to pyrazole, involvement ofADH’ (EC 1.1.1.1). Partially purified ADH from porcine liver cytosol catalyzed the four-electron reduction ofp-nitrosophenol (pNSP) to p-aminophenol (PAP) via transient formation of an enzyme-bound intermediate of pNSP and two-electron transfer from one molecule of NADH (5). Furthermore, purified horse liver ADH (9,lO) and yeast ADH (11) catalyzed NADH-dependent reduction of p-nitroso-NJV-dimethylaniline to the corresoonding amine. . Step 1 Step 2 We have previously reported that rat liver cytosol catalyzed