(tANA) methyltransferase activity, urinary excretion levels of tRNA degradation products, and tRNA base composition in normal monkeys and in those with hepatocellular carcino

This investigation was designed to explore transfer ANA (tANA) methyltransferase activity, urinary excretion levels of tRNA degradation products, and tRNA base composition in normal monkeys and in those with hepatocellular carcino mas induced by N-nitrosodiethylamine. After the develop ment of the tumor, 24-hr urine specimens were collected, the monkeys were sacrificed, and the livers were removed for tRNA isolation and methyltransferase activity studies. The tRNA methyltransferase activity and capacity and the urinary excretion levels for selected tRNA degradation products (pseudounidine, N2,N2-dimethylguanosine †1̃methylinosine, 7-methylguanine, and /3-aminoisobutyric acid) were elevated for the hepatoma-beaning monkeys when compared to those with normal liver. The isolated tRNA pools were analyzed by high-resolution liquid chro matography, and similar base compositions were found for the hepatoma-beaning and normal monkeys. With the use of methyl-deficient Escherichia coli tRNA as the methyl recep ton and the analytical procedure for tRNA analysis, the methylating ability of the tANA methyltransferases in hepa toma and normal liver extracts was determined. The hepa toma methyltransfenase homogenates were found to pro duce increased levels of 7-methylguanine, N2,N2-dimethyl guanine, and thymine, while the normal liver extracts gave higher levels of N2-methylguanine. These differences were not apparent in the base composition of the tRNA pools. The increased urinary excretion and higher methyltransfer ase activity of the hepatoma-beaning monkeys without an apparent increase in the methylated base content of their tANA suggest increased tRNA turnover. However, subtle changes in the methylated base content of individual isoac cepting tRNA's would be missed by analyzing the tRNA pools. The variations in the individual tRNA methyltransfer ase activities of the hepatoma and normal liver homoge nates indicate a difference in the methylation of their tRNA's.