Glutamine Synthetase. Iv.its Formation in Rat Liver following Partial Hepatectomy and during Repletion.

The change in glutamine synthetase activity has been studied under two conditions of liver growth, namely, mitotic growth after partial hepatectomy and nonmitotic growth during repletion after a fast. The surgical operation caused the enzyme activity in the liver to diminish to one half its normal value within one week after the operation and to remain at this reduced level for the duration of the experiment lasting 90 days. A second partial hepatectomy lowered the synthetase activity still further. The lowering appeared to have resulted from an impairment in the synthesis of the enzyme, which was associated with the high mitotic activity of the liver, and presumably with the de novo synthesis of deoxyribonucleic acid. Furthermore, partial hepatectomy did not affect the kidney enzyme, nor did unilateral nephrectomy decrease the liver enzyme. A temporary fall in the liver synthetase activity resulted from repleting after a fast; the fall depended on the diet of repletion, being greater on a low protein diet than on a high protein diet. Conversely, the kidney enzyme of the rat during repletion rose to a higher level on a low protein diet than on a high protein diet. Raising the glutamine content in the diet did not reduce the synthetase activity in rat liver, nor did omitting glutamine from the diet increase the enzyme activity. A protein-free diet, however, proved to be more detrimental to the enzyme in liver than fasting, which brought varied effects on the enzyme depending on its duration.