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Reaction of Polycyclic Hydrocarbon-Cysteine Conjugates with the Aminoacyl-RNA Synthetase System¹

Department of Biochemistry, University of Tennessee Medical Units, Memphis, Tennessee 38103

A number of arylcysteine derivatives, which are metabolites of polycyclic aromatic hydrocarbons, have been synthesized. These amino acid analogs were tested for their ability to act as substrates for aminoacyl-RNA synthetases in an in vitro system using enzyme fractions of bakers' yeast. These studies have shown that S-(p-chlorophenyl)-L-cysteine, S-(9, 10 dihydro-9-hydroxy-10-phenanthryl)-L-cysteine, S-(5,6- dihydro-6-hydroxy-5-benz(a)anthryl)-L - cysteine, S-(5, 6- dihydro-6-hydroxy-5-dibenz(a, h)anthryl-L-cysteine, and S-(7-benz(a)anthryl)-methyl-L-cysteine are activated and transferred to tRNA. The arylcysteines were observed to compete with a variety of natural amino acids. This investigation revealed that chlorophenylcysteine competed with arginine; dihydrohydroxyphenanthrylcysteine competed with glutamic acid, phenylalanine, and histidine for activating enzymes; dihydrohydroxybenzanthrylcysteine likewise competed with arginine and phenylalanine; and dihydrohydroxy-dibenzanthrylcysteine competed with methionine and leucine. Thus, the structure of the hydrocarbon moiety conjugated with the sulfhydryl group of cysteine determines in particular the synthetases involved in amino acid activation. Moreover none of the cysteine conjugates were activated by the cysteinyl-RNA synthetase. Hydrocarbons are bound to protein by this pathway at sites different from those resulting from direct interaction.

¹ This investigation was supported in part by USPHS Research Grant CA-01228 from the National Cancer Institute and by USPHS Research Grant AM-09131 from the National Institute of Arthritis and Metabolic Diseases.

Received 11/22/68. Accepted 6/ 3/69.