Summary. The hydrolysis of glutamine by rat liver preparations occurred through a phosphate-dependent reaction differing from the one in rat kidney preparations primarily in its greater affinity for phosphate. The two enzymes also differed in pH optima, affinity for glutamine, reactions with various activators and inhibitors, and distributions in tissues. Both enzymes were mitochondrial, but retained their distinctive differences after sonication and in mixtures. The conditions for the independent assay of each type of activity in tissues are described. The liver type of reaction was limited to adult and regenerating liver, while high activities of the kidney-type of reaction were found in brain, kidney and small intestine and lesser activities in a variety of other tissues, including fetal liver and hepatoma. A third type of activity occurred independently of phosphate addition and comprised onesixth of the total in kidney preparations and less in other tissues.

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Significant amounts of arginase activity were found in homogenates of submaxillary salivary gland and epididymis, as well as of liver, kidney, mammary gland, and small intestine. The isoelectric point of arginase solubilized from kidney was at pH 7.0 in contrast to that of pH 9.4 characteristic of hepatic arginase in rat. The isozymic variants of arginase in the different tissues were identified by their electrophoretic migration on polyacrylamide gels and by titration of the enzymes against antibody prepared against purified rat liver arginase. Antibody titrations confirmed the indications obtained by electrophoresis that one type of arginase is limited to hepatic tissues (and possibly submaxillary gland) while the other type is found in all other tissues. The physiological role of arginase in hepatic tissues has been previously associated with the urea cycle; the possible function of arginase in proline synthesis in other tissues remains to be substantiated.

An assay is described for the quantitative measurement of asparaginase in crude preparations of rat tissues. Most of the asparaginase is concentrated in the liver, in the cytosol, with a Km of 4.71 X 10^-3M for asparagine. The activity is twice as high in adult female as in male liver; this sex difference develops after the 50th postnatal day. Adult kidney contains significant asparaginase activity (25% of that in liver); fetal tissues contain none. Asparaginase is undetectable in transplanted neoplasias with high glutaminase activity. Asparaginase appears in the liver immediately after birth and rises during the ensuing 5 days. Then, after a week of constancy, it rises again to reach adult values (in the male) on about the 20th postnatal day. Separation from the mother prevents the neonatal rise of asparaginase but not that of other liver enzymes. In 8- to 14-dayold rats an injection of hydrocortisone causes a major rise in the level of asparaginase. The results suggest that the physiological stimulus that promotes the first phase of accumulation of rat liver asparaginase is related to nursing and that adrenocortical secretion, known to increase after the 10th postnatal day, promotes the second phase of accumulation of this enzyme.