TIME-DEPENDENCE OF ETHIONINE-INDUCED CHANGES IN RAT-LIVER TRANSFER-RNA METHYLATION

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 37  (3) , 865-869
Abstract
Methyl-deficient tRNA and subnormal levels of tRNA-methylating enzymes were found in the liver of female rats that received injections of 250 mg DL-ethionine/kg body weight per day and 120 mg adenine/kg body weight per day for 2 days. Adenine alone had no effect. When the ethionine plus adenine injections were continued for longer periods of time, liver tRNA methylating enzyme activity measured in vitro gradually increased and exceeded that of the controls. The relative methyl deficiency of liver tRNA decreased. The latter was evident because of the decreased ability of tRNA to accept methyl groups during in vitro methylation catalyzed by homologous enzymes. Liver tRNA from animals that were treated with ethionine for 7 days could accept only about 40% as many methyl groups as tRNA from animals that received ethionine for only 2 days. No further significant change in methyl deficiency of the tRNA was seen when ethionine administration was extended to 14 days. Enzyme preparations from ethionine treated, but not control, rat liver contained dialyzable substances that inhibited the tRNA methylases and altered the base specificity of these enzymes. Although S-adenosylhomocysteine and S-adenosylethionine were present in the liver preparations, neither of these substances could account for the observed changes in specificity.

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