Adaptive Changes of Phosphofructokinase and Aldolase in Adipose Tissue

The activity of several enzymes of the glycolytic pathway was investigated in rat epididymal adipose tissue. Determination of phosphofructokinase and aldolase activity with an improved assay involving homogenization of the tissue in the presence of fructose 6‐phosphate showed that the activity of aldolase is in the same range or lower than that of hexokinase and phosphofructokinase. Both aldolase and phosphofructokinase exhibited an adaptive behavior. The activity at optimal assay conditions decreased in fasting or alloxan diabetic rats and rebounded on refeeding or upon treatment of diabetic rats with insulin. These changes are similar to those of hexobase and glucose‐6‐phosphate dehydrogenase, whereas the activity of pyruvate kinase was not influenced by these situations. Changes in the steady state concentrations of glycolytic intermediates in vivo provided further evidence that the activity of aldolase may intluence the rate of glycolysis in adipose tissue. A rise in fructose 1,6‐bisphosphate concentration relative to that of fructose 6‐phosphate was observed, especially in conditions of increased glucose flow. A rise in both fructose &phosphate and fructose 1,6‐bisphosphate was observed in diabetic rats. The pattern of activities of glycolytic enzymes and of metabolite concentrations in adipose tissue is compared with that in other tissues, and the regulatory characteristics of glycolysis peculiar to adipose tissue are discussed.