The reductive cleavage of 4-dimethylaminoazobenzene by rat liver; the intracellular distribution of the enzyme system and its requirement for triphosphopyridine nucleotide

G C MUELLER, J A MILLER
1949 Journal of Biological Chemistry  
The hepatic carcinogen, 4-dimethylaminoazobenzene, and its metabolites are subject to at least three metabolic reactions in the intact rat: stepwise demethylation of the dimethylamino group; hydroxylation, principally at the 4' position; and reductive cleavage of the azo linkage to yield monophenylamines (l-3). Although the exact sequence of these reactions and the extent to which each occurs in vivo are unknown, it is now possible to study each of these reactions in vitro with rat liver
more » ... th rat liver homogenates. Thus, in an earlier communication (4) it was reported that freshly prepared rat liver homogenates, fortified with hexose diphosphate, diphosphopyridine nucleotide, and nicotinamide, metabolized 4-dimethylaminoazobenzene with formation of small quantities of the demethylated intermediates, 4-monomethylaminoazobenzene and 4-aminoazobenzene, and a new metabolite, 4'-hydroxy-4-dimethylaminoazobenzene. The major reaction, however, appeared to involve a destruction of the azo linkage, since more dye disappeared in these reaction mixtures than could be accounted for by the azo metabolites found. The present communication deals with the mechanism of the disappearance of the azo dye in vitro when incubated with rat liver homogenates. This reaction has been found to consist of the reductive cleavage of the azo linkage in the dye. Furthermore, it has been possible to demonstrate a specific requirement for reduced triphosphopyridine nucleotide as the electron donor for the cleavage reaction and to show the localization of certain components of the enzyme system within the hepatic cell. Methods For these experiments triphosphopyridine nucleotide concentrates were prepared by a new procedure developed in this laboratory (5). These
pmid:18139207 fatcat:l6br6dsg6nfpbaeymguumizyey