Effect of glucose-6-P on the catalytic and structural properties of glycogen phosphorylase a.

Kinetic studies of muscle phosphorylase a in cationic buffer (pH 6.8) demonstrate that glucose-6-P competitively inhibits the binding of the substrate, glucose-1-P, to the enzyme. The inhibitory effect of glucose-6-P is largely overcome by glycerol-2-P. AMP counteracts inhibition of the enzyme by glucose-6-P, while glucose and glucose-6-P can interact to produce a synergistic inhibition of phosphorylase a activity. Preincubation of phosphorylase a with glucose-6-P at 20 degrees C results in approximately 3-fold increase in activity, while ultracentrifugation experiments carried out under the same conditions showed that phosphorylase a can be converted to dimers by glucose-6-P.