Kinetic properties of alpha-glucan phosphorylase from Indocibium guttattam

The kinetic properties of alpha-glucan phosphorylase b (alpha-D-1,4-glucan : orthophosphate alpha-D-glucosyltransferase, EC 2.4.1.1) purified from a deep-sea fish Indocibium guttattam were studied in the direction of glycogen synthesis. There was no homotropic site-site interaction between glucose 1-phosphate sites and between glycogen sites. However, heterotropic interaction was observed between substrate and activator sites. The kinetic data obtained for the fish enzyme were consistent with the rapid equilibrium random mechanism reported for alpha-glucan phosphorylase from other sources. All the dissociation constants were 2-3 times higher for the fish enzyme than for the rabbit enzyme. Although the fish enzyme exhibited a greater affinity for AMP at 30 degrees C as compared to the rabbit enzyme, these sites were characterized by a lack of homotropic cooperativity. Heterotropic cooperativity was observed between AMP and glucose 1-phosphate sites.