Studies on the enzymatic reduction of C-nitroso compounds. III. The kinetic analysis of C-nitrosoreductase reaction catalyzed by the cytoplasmic enzyme from porcine liver.

The reaction kinetics of the major cytoplasmic NADH-nitrosoreductase, which is the identical enzyme to alcohol dehydrogenase [EC 1.1.1.1], was studied with a partially purified preparation from porcine liver. On the basis of the data obtained, the following scheme is proposed as the mechanism of this enzyme reaction: [Formula: see text], where E and E' are the enzyme unit (one subunit of alcohol dehydrogenase) and an intermediate form of the enzyme unit-substrate compound which appears by two-electron reduction of the enzyme unit-substrate compound, respectively, S is p-nitrosophenol (p-NSP), N is NADH, and P1 and P2 are NAD+ and p-aminophenol (p-AmP), respectively. In this case, it is assumed that k1 less than K2. Para-aminophenol, the reaction product, showed an inhibition competitive to p-NSP at fixed concentrations of NADH and also showed a mixed-type inhibition to NADH at fixed concentrations of p-NSP. NAD+ inhibited the reaction in a competitive manner to NADH at fixed concentrations of p-NSP and in a non-competitive manner to p-NSP at fixed concentrations of NADH. These results can also be accounted for by the proposed mechanism.