Regulation of fructose-6-phosphate 2-kinase by phosphorylation and dephosphorylation: possible mechanism for coordinated control of glycolysis and glycogenolysis.

Abstract

The kinetic properties and the control mechanism of fructose-6-phosphate 2-kinase were investigated. The MW of the enzyme is .apprxeq. 100,000 as determined by gel filtration. The plot of initial velocity vs. ATP concentration is hyperbolic with a Km of 1.2 mM. However, the plot of enzyme activity as a function of fructose 6-phosphate is sigmoidal. The apparent K0.5 for fructose 6-phosphate is 20 .mu.M. Fructose-6-phosphate 2-kinase is inactivated by the catalytic subunit of [porcine] cAMP-dependent protein kinase, and the inactivation is closely correlated with phosphorylation. The enzyme is also inactivated by [rabbit muscle] phosphorylase kinase in the presence of Ca2+ and calmodulin. The phosphorylated fructose-6-phosphate 2-kinase, which is inactive, is activated by phosphorylase phosphatase and alkaline phosphatase. The possible physiological significance of these observations in the coordinated control of glycogen metabolism and glycolysis is discussed.