ABSTR A CT The behaviour of rat kidney cortex phosphoenolpyruvate carboxykinase has been investigated under conditions of triamcinolone administration and ammonium chloride acidosis. The concentration of phosphoenolpyruvate carboxykinase as measured by enzyme activity and immunotitration was elevated under both conditions. The mechanism of induction is different in the two cases. At doses which produce maximum stimulation, the effects of steroid and ammonium chloride were additive; only the increment in enzyme activity produced by steroid was blocked by actinomycin D.Phosphoenolpyruvate carboxykinase activities in all conditions investigated show similar behavior in dilute extracts; these experiments involved antibody titration, stability studies, and molecular weight determinations on sucrose gradients.The molecular weight of phosphoenolpyruvate carboxykinase was also studied in undiluted extracts prepared by high-speed centrifugation; values were determined from sedimentation data obtained with a movingpartition cell as described by Yphantis and Waugh. Under these conditions, the apparent molecular weight of phosphoenolpyruvate carboxykinase was increased from 83,000 to 128,000 by ammonium chloride acidosis.These results are discussed and a hypothesis regarding the mechanism of phosphoenolpyruvate carboxykinase regulation in kidney cortex is presented.

Aminooxyacetate is a potent inhibitor of glutamate: oxaloacetate transaminases from both rat and guinea pig kidney cortex. In guinea pig kidney cortex, phosphoenolpyruvate carboxykinase activity was found to be 59% cytoplasmic, 41% mitochondrial. Mitochondrial phosphoenolpyruvate carboxykinase activity is expressed only after sonication indicating that the enzyme is located within the inner mitochondrial membrane. Aminooxyacetate inhibits gluconeogenesis from lactate, but not from pyruvate, in both rat and guinea‐pig kidney cortex. It is concluded that gluconeogenesis in guinea‐pig kidney cortex proceeds by a pathway involving cytoplasmic, rather than mitochondrial phosphoenolpyruvate carboxykinase.

A B S T R A C T The kinetics of the induction of rat kidney phosphoenolpyruvate carboxykinase activity after triamcinolone and ammonium chloride administration have been investigated with a view to the further differentiation of the two processes.The half-life of kidney phosphoenolpyruvate carboxykinase activity, as measured from the decay curve after a single doses of triamcinolone, is approximately 1.4 hr.This compares with a half-life for the enzyme from acidotic kidney of approximately 3.4 hr.Analysis of the data indicates that the induction of phosphoenolpyruvate carboxykinase activity by triamcinolone may be attributed to an increase in de novo protein synthesis. Induction by acidosis is qualitatively distinct and is partly attributed to a reduction in the rate of decay of phosphoenolpyruvate carboxykinase activity.The activities of the gluconeogenic enzymes glucose-6-phosphatase, fructose-1,6-diphosphatase, and phosphoenolpyruvate carboxykinase in both liver and kidney have been measured in animals separately treated with triamcinolone and ammonium chloride. Triamcinolone significantly increases the activities of liver phosphoenolpyruvate carboxykinase, kidney glucose-6-phosphatase, and kidney phosphoenolpyruvate carboxykinase only; ammonium chloride stimulates a 200% increase in kidney phosphoenolpyruvate carboxykinase, but has no effect on the other enzymes.

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