The behavior of the activity of
arginyl-tRNA synthetase (
L-arginine :
tRNAArg Ligase(
AMP-forming), EC 6.1.1.19) was determined in extracts of rat liver: normal adult, normal proliferating (from developing and from partially hepatectomized rats), and neoplastic (
hepatomas of different growth rates) and in extracts of rat kidney cortex and transplantable kidney
tumors. The Km values for
arginine,
ATP, and
tRNA of the
enzyme of the rapidly growing
hepatoma 3924A were the same as those of the
enzyme from the liver of control rats. The pH optima of the control and neoplastic livers were in the same range of 7.25-8.0. Taking the hepatic specific activity for
arginyl-tRNA synthetase as 100%, deep layer of gut, thymus and testis had higher activity; renal cortex and spleen had the same activity; and skeletal muscle, brain, heart, lung, superficial layer of gut and adipose tissue had lower activity. In a wide spectrum of
hepatomas of different growth rates, a significant increase of 1.4-2.4-fold in
arginyl-tRNA synthetase activity was observed when compared with that of liver of control normal rats. This elevation in
enzyme activity in
hepatomas appears to be specific to
neoplasia, since it is unaltered in regenerating and low in differentiating liver. The increase in
arginyl-tRNA synthetase in the liver
tumors appears to be transformation-linked, since the activity was increased in all
hepatomas, even in the slowest growing ones. Furthermore, the increase in
enzyme activity was not limited to
hepatic neoplasms, since a rise was also observed in transplantable rat kidney
tumors. Thus, the reprogramming of gene expression in neoplastic tissue entails an increase in
arginine-
tRNA synthetase activity.