Enhancement of microsomal aniline and acetanilide hydroxylation by haemoglobin

1. Haemogloblin and myoglobin enhance rat liver microsomal p-hydroxylation of aniline and acetanilide. Microsomal N-demethylation of ethylmorphine and aminopyrine is not increased by haemoproteins. 2. The enhancement of microsomal p-hydroxylation is maximal at high substrate concentration and high haeme compound concentration. 3. Detergent-purified NADPH-cytochrome c reductase, free flavins and manganese ions considerably increase the haemoglobin-mediated, tissue-free hydroxylation of aniline. Microsomal aniline hydroxylation is not enhanced by haeme, ferric ion or albumin. 4 Catalase and cyanide ions are powerful inhibitors of haemoglobin-mediated aniline hydroxylation both in the presence and absence of tissue. Carbon monoxide inhibits the hydroxylase activity of the tissue-free system to a smaller extent than that of a system containing microsomes plus haemoglobin whereas p-chloromercuribenzoate inhibits only the flavoprotein-dependent hydroxylation of aniline mediated by haemoglobin. 5. Several possibilities of interactions between substrate, microsomes and haeme compounds are proposed.