The in vitro formation of protein-bound derivatives of aminoazo dyes by rat liver preparations.

Previous studies have demonstrated the presence of protein-bound aminoazo dyes in the livers of rats fed the hepatocarcinogen 4-dimethylaminoazobenzene (DAB) 1 or certain of its derivatives ( ~ , 35). Since, under a variety of conditions, the levels of these bound derivatives can be correlated with the expected tumor incidence, the formation of the protein-bound dyes appears to be an important step in the genesis of liver tumors by the aminoazo dyes (3~-35, ~7). When the dyes are fed continuously at carcinogenic levels, maximum levels of hepatic bound dye are reached at 1-3 weeks with the most carcinogenic dyes and at later times with less active compounds. Comparable levels of protein-bound dye are found in the liver within 1~-~4 hours after a single large dose of dye is administered orally or intraperitoneally (11, 16, 37). The protein-bound dyes formed under each of these in vivo conditions appear to be similar in most respects (11), although Terayama et al. (37) reported spectral differences between the polar fractions obtained by proteolytic hydrolysis of the liver protein from rats fed dye continuously or given a single large dose. This paper reports the formation of protein-bound derivatives of the dyes by slices, homogenates, and isolated particulate fractions of rat liver. However, these bound derivatives differ in several respects from those formed in vivo, and their relationship to the latter is not