Substrate Specificity of Adenine-Specific Transfer RNA Methylase in Normal and Leukemic Tissues.

High speed supernatant enzyme fractions derived from each of three tissues (livers and spleens of normal rats, and spleens of rats with the Dunning leukemia) were compared in their ability to transfer methyl groups from S-adenosyl-methionine to Escherichia coli transfer-RNA (tRNA). In comparison to the supernatant fractions from the normal tissues, that from leukemic spleen had a six-fold higher tRNA methylase activity and methylated E. coli tRNA to a much higher extent. A tRNA methylase which methylated adenine in the 1-position was isolated from each high speed supernatant fraction by DEAE-cellulose and Sephadex G-200 chromatography. Although the purified leukemic spleen enzyme contained six-fold higher methylase activity, it. methylated E. coli, yeast, and mammalian tRNA to the same extent as did the corresponding enzyme from normal liver or spleen. The normal and leukemic tissue enzyme preparations appeared to methylate the same sequences in E. coli tRNA, and could methylate this tRNA to an extent of about one methyl group per molecule. The results suggest that in comparison to that of normal tissue, 1-adenine methylase in the leukemic spleen tissue is increased in activity but possesses identical substrate specificity. [ABSTRACT FROM AUTHOR]