title: Interaction of normal and tumor transfer RNA methyltransferases with ethionine-induced methyl-deficient rat liver transfer RNA.
abstract: The tRNA methyltransferases from normal rat liver and Novikoff hepatoma have been compared with respect to their base specificity, capacity to methylate, and reaction kinetics, using mixed Escherichia coli B transfer RNA (tRNA) and ethionine-induced partially methyl-deficient rat liver tRNA. The pattern of base methylation of the two substrates is different with the use of enzymes from either source. In particular, N1-methylguanine methylation is much greater in the methyl-deficient rat liver tRNA. The enzymes from the two sources also show differences in specificity of base methylation in either substrate, particularly in the percentage of N2-methylguanine synthesized. The Novikoff hepatoma enzymes have a greater capacity for methylation with either type of tRNA than do rat liver enzymes. The methyl-deficient rat liver tRNA is a poorer substrate for the enzymes from both sources than is E. coli B tRNA in terms of rate of methylation as well as total acceptance of methyl groups. The affinity constants are somewhat higher for the methyl-deficient rat liver tRNA than for E. coli B tRNA. The Novikoff hepatoma enzymes, in general, have larger affinity constants than the rat liver enzymes. Maximal velocities for the various base-specific enzymes are lower with the methyl-deficient rat liver tRNA, with the exception of the 1-methylguanine specific enzymes. These enzymes from either rat liver or Novikoff hepatoma exhibit approximately a 2.5-fold greater maximal velocity with methyl-deficient rat liver tRNA.
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D004926:Escherichia coli / Q000201:enzymology; D005001:Ethionine / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008113:Liver Neoplasms / Q000201:enzymology*; D008745:Methylation; D009374:Neoplasms, Experimental / Q000201:enzymology; D012334:RNA, Neoplasm; D012343:RNA, Transfer; D051381:Rats; D012359:tRNA Methyltransferases / Q000378:metabolism*
chemical_list: D012334:RNA, Neoplasm; D012343:RNA, Transfer; D012359:tRNA Methyltransferases; D005001:Ethionine