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O-demetnylation of biochanin A and some other isoflavones and methylated estrogens by microsomal liver enzymes


, : O-demetnylation of biochanin A and some other isoflavones and methylated estrogens by microsomal liver enzymes. Ark Kemi 21(2): 97-121

An enzyme system in the liver of a number of animal species is described. This enzyme system catalyzes the O-demethylation of biochanin A, formononetin and some other methoxylated isoflavones and estrogens into the corresponding phenol compound and formaldehyde. Like the enzymes of various oxidative reactions concerned with e.g. hydroxylation of steroids and detoxification of drugs this enzyme system was found to be located in the microsomes and to require both the reduced pyridine nucleotides and oxygen. The relations between biochanin A demethylation and other microsomal oxidase reactions are discussed. Data are given concerning the rate of biochanin A demethylation in test systems including different inhibitors and competitive substrates. The biochanin A demethylating enzyme system was found to agree with other oxidative microsomal enzymes in a number of ways, but differed in some respects. Cyanide inhibited the biochanin A demethylation but stimulated the demethylation of other methoxylated compounds. Peroxidase, but not catalase, caused an inhibition of the enzymatic activity. Fe++ stimulated the reaction, and the enzyme system was sensitive to reagents known to react with metal-dependent enzymes. SH inhibitors, heavy metals, and Mn++ strongly inhibited the reaction. Some evidence was found for substrate specificity of the biochanin A demethylating enzyme system.

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