Further Studies on the Phosphorylation and Kinetics of Rat Liver Fructose-1, 6-Bisphosphatase: Importance of the Three-Dimensional Structure of a Substrate to Protein Kinase A

Abstract

Rat liver fructose-1, 6-bisphosphatase was phosphorylated by cAMP-dependent protein kinase to 2.6 mol phosphate/mol subunit but not by Ca²⁺/phopholipid-dependent and Ca²⁺/ calmodulin-dependent protein kinases. It was demonstrated that phosphorylation of Ser-341 and Ser-356, and to a much lower extent, Ser-338, was dependent on the presence of intact arginine residues. This observation implicates that the intact three-dimensional structure of the substrate is necessary for phosphorylation of Ser-356 since the closest arginine is located at a six amino acid residue distance.