The enzymatic reduction of nicotinamide N-oxide.

An enzymatic system which reduces nicotinamide N-oxide to nicotinamide was isolated from hog liver and purified about 280-fold. The reduction is dependent on the presence of reduced diphosphopyridine nucleotide or a low molecular weight constituent found in boiled liver supernatant. The two cofactors appear to be involved in the expression of two distinct enzymatic activities. Evidence has been presented which indicates both activities may be associated with a single protein or enzymatic unit. The DPNH-dependent reaction is the following.