Structural and kinetic properties of glycogen phosphorylase a from fat body of the silkworm, Bombyx mori

Abstract

1. 1. Glycogen phosphorylase b was isolated from the pupal fat body of Bombyx mori, and phosphorylated to the a form by phosphorylase kinase purified from the same tissue. 2. 2.|The structural and kinetic properties of the two forms of fat body phosphorylase were compared. 3. 3. The mol. wts of phosphorylase a estimated by gel filtration HPLC and SDS-gel electrophoresis were found to be 95,000 and 90,000 respectively, indicating that the enzyme is a monomeric protein (as is the b form). 4. 4. The S 20 (sedimentation coefficient) value of phosphorylase a obtained by a sucrose density gradient centrifugation was 7.8, which is somewhat larger than 6.9 of the b form, suggesting some conformational changes have occurred during the phosphorylation. 5. 5. The a form has 2- to 3-fold higher affinity for both substrates, glycogen and inorganic phosphate (Pi), compared to the b form.