[Estimation of kinetic constants and study of site specificity of Zajdela ascite hepatoma and rat liver tRNA-methylases].

Individual yeast tRNAVal1 was used as a substrate for estimation of kinetic constants and study of site specificity of m5C-and m1A-methylases of Zajdela ascite hepatoma and rat liver. It was demonstrated that the rate of yeast tRNAVal1 methylation by hepatoma tRNA-methylases is 4--5 times higher than that induced by liver tRNA-methylases. The rates of 1-hour methyl groups incorporation into tRNAVal1 were 3.7 and 4.7 times higher in case of m5C-and m1A-methylases and 9.4 and 4.5 times higher in case of m1G-and m7G-methylases of hepatoma than the respective rates obtained for corresponding liver methylases. The main products of methylation were m5C and m1A containing about 90% of total radioactivity incorporated into tRNA. m5C-methylases of liver and hepatoma had similar affinity for S-Ad-Met. The Km value for both enzymes was 2.66 micronmole; the Km values for m1A-methylases of liver and hepatoma with respect to S-Ad-Met were the same and equal to 0,25 micronmole. m5C and m1A methylases of liver and hepatoma had adequate affinity for yeast tRNAVal1; their site specificity was the same, since they methylated in yeast tRNAVal1 cytosine in the tetracytidylic sequence of C49--C52 and adenine in the 59th position from the 5'-end of the molecule.