Regulation of glucose uptake by muscle. 6. Fructose 1,6-diphosphatase activity of rat heart and rat diaphragm

Abstract

The fructose 1,6-diphosphatase activity of rat heart and diaphragm muscle was investigated by measurement of the rate of formation of fructose 6-phosphate and inorganic phosphate from fructose 1,6-diphosphate. The fructose 1,6-diphosphatase activity of extracts of diaphragm or of hearts from normal rats (starved for 18 or 30 hours) or from alloxan-diabetic rats was extremely low (0-5.7 umoles of product formed/g. of wet muscle/hr.) and not more than 5% of that of comparable extracts of rat liver. It is also extremely low by comparison with the phosphofructokinase activity of extracts of rat heart (45 umoles/ g./hr.). It is concluded that there is very little, if any, fructose 1,6-diphosphatase in rat heart or diaphragm muscle; that changes in the overall rate of phosphorylation of fructose 6-phosphate in these tissues must be brought about by alterations in the activity of the phosphofructokinase step; and that the activity of fructose 1,6-diphosphatase is too low to permit significant reversal of glycolysis to take place in these tissues.