Electrophoretic changes in proteins from livers of rats fed 4-dimethylaminoazobenzene.

INTRODUCTION Miller and Miller (3) showed that the carcino genic dye, 4-dimethylaminoazobenzene, is firmly bound to protein constituents of the rat liver. Such protein-binding reaches a maximum after 4-6 weeks on the azo diet, whereas the neoplasm arises several weeks later. Moreover, the neoplastic tis sue contains essentially no protein-bound dye. Hence, Miller and Miller (3) have postulated that certain protein constituents of the cell, which are normally capable of binding the azo dye, are lost or permanently altered in the course of the car cinogenic process. This hypothesis has'received support from the recent work ¿Õ Soroi affd Cohen (6), who found that, in consonance with the pro tein-depletion hypothesis, thjere-iea decrease in the percentage composition of me relatively slow electrophoretic components present in extracts of the neoplastic tissue. In addition, Sorof et al. (7) have shown that most of the protein-bound dye mi grate»with the slow electrophoretic components. Hence, the hypothesis of the loss or alteration of dye-binding protein would seem to be well sup ported by this as well as other evidence. The neoplastic type of electrophoretic pattern (increase in percentage composition of faster com ponents with decrease of the slower components) was found by Sorof and Cohen (6) to occur only in the neoplastic tissue itself, and not in the adjacent normal liver tissue. In the present experiments we have confirmed the alteration of electrophoretic components as described by Sorof and Cohen. However, with the preparative method here used, which differs in several respects from that of Sorof and Cohen, the livers of rats fed the noncarcinogenic azo dye, 4-aminoazobenzene, and also the livers of young rapidly growing rats, show the same type of electrophoretic pattern found in the neoplastic tissue. In our animals, too, the preneoplastic livers show the same electrophoretic