The effects of fasting, diabetes, and hypophysectomy on rat adipose pyruvate kinase.

Abstract

Pyruvate kinase in rat adipose tissue, unlike liver pyruvate kinase, has been reported to be unresponsive to fasting and the diabetic state. Levels of this enzyme in liver tissue are diminished as a response to these conditions. We have reexamined the responsiveness of adipose pyruvate kinase using DNA as a measure of cell number rather than protein content as previously used. Under these conditions we observed a significant reduction in adipose cell pyruvate kinase levels in fasting, diabetes, and hypophysectomy. The protein synthesis inhibitor, cycloheximide, given concurrently with the fasting regimen or the induction of diabetes prevents the loss of pyruvate kinase which otherwise would be observed. Presumably protein, possibly a protease, must be synthesized to permit a decrease in pyruvate kinase under fasting and diabetic conditions. Phosphate ion is demonstrated to inhibit the reduction in pyruvate kinase levels observed under some of these metabolic conditions.