Activation and Incorporation of Arylcysteines into Ribosomal Protein.

The metabolic interaction of aromatic hydrocarbons with cellular constituents leads to the formation of hydrocarbon-protein conjugates. Such binding has been implicated in carcinogenesis by polycyclic aromatic hydrocarbons (1). Previous evidence (2-4) has indicated that the hydrocarbon-protein conjugate can be a donor of the substituted cysteine moiety for mercapturic acid formation. S-ilrylcysteines, or certain of their dihydrohydroxy derivatives, have been found to arise in tissues from the original protein conjugate (3) and from S-dihydrohydroxyarylglutathiones (5, 6). The generation of S-substituted cysteines in tissues by metabolic processes offered a mechanism for formation of hydrocarbon-protein conjugates alternative to direct binding. This would involve the pathway for incorporation of amino acids into proteins. This hypothesis was tested by studying the activation and incorporation of X-(p-chlorophenyl)-L-cysteine and S(1,2,3,4-tetrahydro-2-hydroxy-l-naphthyl)-~-cysteine into ribosomes. A purified system from rat liver catalyzed the activation and transfer of the substituted cysteine to soluble ribonucleic acid. The aminoacyl-soluble-ribonucleic acid, in the presence of supernatant fraction, incorporated the arylcysteine into deoxycholate particles (ribosomes) of rat liver.