ELECTROSTATIC EFFECTS IN THE CONTROL OF GLYCOGEN-PHOSPHORYLASE BY PHOSPHORYLATION

Electrostatic effects are important in the initial activation mechanis m of glycogen phosphorylase by phosphorylation. Analysis of the electr ostatic surface potential of glycogen phosphorylase with the program G RASP shows that in the unphosphorylated state, the N-terminal 20 resid ues, which include a number of basic amino acids, are located close to a position on the surface of the molecule that is highly acidic. Upon phosphorylation by phosphorylase kinase at Ser 14, the N-terminal res idues change their position and conformation so that the Ser-P is dire cted away from the acidic patch and to an intersubunit site where 2 ar ginines bind the phosphate. This recognition site is created through t ertiary and quaternary structural changes that accompany the activatio n mechanism.