A comparative study of glytaminase isozymes in rat tissues.
The three kinds of glutamineses in rat kidney and liver were defined in comparative terms by their properties and were separately purified. Substantial purification was obtained by polymerization and depolymerization of the kidney isozyme that is activated by phosphate, These isozymes differ most strikingly in the activators of their reactions:maleate and a high concentration of phosphate, respectively, for the two kidney isozymes, and a low concentration of phosphate for the liver isozyme. The kidney isozyme that is activated by phosphate was also activated by a much lower concentration of ATP and by other complex phosphates. They also differ in physical properties: the maleate-activated isozyme was heat resistant (50 degrees C) and associated with insoluble submitochondrial particles; both phosphate-activated isozymes were heat sensitive and could be solubilized from their respective mitochondria; the phosphate-activated isozyme of kidney polymerized in phosphate-borate solution while that of liver did not. The characteristics of the kidney isozyme that was activated by high phosphate were shared by the glutaminases in adult brain, transplanted tumors, and in fetal liver and kidney. The similarity to the kidney enzyme was confirmed by the use of polymerization in phosphate borate of the isozyme from a mammary carcinoma to effect its purification.