Glycogen Phosphorylase Protein Research Articles

Structural and Functional Characterization of theDrosophilaGlycogen Phosphorylase Gene

We identified a P element insertional mutant of theDrosophilaglycogen phosphorylase (DGPH) gene. Glycogen phosphorylase protein concentration and enzyme activity are decreased while glycogen content is increased in flies homozygous for the mutant allele. TheDGPHgene has been cloned and sequenced; its open reading frame codes for a protein of 844 amino acids with a predicted molecular mass of 97 kDa. Comparison of the conceptual amino acid sequence of theDrosophilaglycogen phosphorylase with glycogen phosphorylase sequences from other organisms shows a high degree of homology to mammalian enzymes. All the residues of the allosteric effector binding sites, the active site, and the site of phosphorylation are exactly conserved, but some of the residues of the glycogen storage site are not.

Identification of an S100 target protein: glycogen phosphorylase

An S100 binding protein from skeletal muscle, R95 000, has been purified, identified as glycogen phosphorylase, and shown to be regulated in vitro by the S100α isoform. When a soluble skeletal muscle fraction was subjected to a standard purification procedure for glycogen phosphorylase, R95 000 copurified with the 95 000 molecular weight glycogen phosphorylase protein standard on SDS-polyacrylamide gels, as well as having glycogen phosphorylase activity. In addition, purified glycogen phosphorylase a and b interacted with both S100 isoforms, S100α and S100β, by gel overlay and affinity chromatography. While S100β had no effect on the enzymatic activity of glycogen phosphorylase a, S100α inhibited the enzymatic activity of glycogen phosphorylase a in a calcium-independent manner. Altogether, these data suggest that glycogen phosphorylase may be an intracellular S100α target in skeletal muscle fibers. Furthermore, these results suggest that the inhibition of glycogen phosphorylase a activity may be responsible for the lack of fatigability of slow-twitch fibers, which express S100α, when compared to fast-twitch fibers, which do not express S100 proteins.

A novel inhibitor of glycogen phosphorylase from crayfish hepatopancreas

1. 1. A novel glycogen phosphorylase inhibitor was partially purified from crayfish hepatopancreas. 2. 2. The inhibitor was found only in two species of crayfish examined, and not in lobster, fresh and salt water clams, mussels or cockroaches. 3. 3. The inhibitor is a small protein ( M r = 23,000) which did not show proteolytic activity. 4. 4. Preliminary kinetic analysis of the inhibitory mechanism indicated that it bound to both glycogen and the glycogen phosphorylase protein. 5. 5. Inhibitor binding to glycogen resulted in a competitive inhibition pattern with respect to glycogen phosphorylase (inhibition constant of ca 10 μg/ml). 6. 6. The inhibitor also bound glycogen phosphorylase directly with a binding coefficient of 100 μg/ml resulting in a partially non-competitive inhibition pattern with respect to phosphate.

Regulation of rat liver glycogen phosphorylase concentration by in vivo relative levels of glucagon and insulin.

The concentrations of glycogen phosphorylase protein were determined by rocket immunoelectrophoresis in liver extracts from rats that had artificially induced altered hormonal patterns. These levels were compared with measurements of total phosphorylase activity. Minipump-induced chronic hyperglucagonemia and streptozotocin-induced diabetes resulted in 47% and 67% decreases, respectively, in total phosphorylase activity along with corresponding 52% and 68% drop, respectively, in phosphorylase protein levels. Insulin replacement in diabetic rats returned both parameters to control values. Minipump-induced hyperinsulinemia or injection of glucagon antiserum, T3, or propylthiouracil had no effect. The results of this study indicate that conditions which lead to an elevation of the glucagon to insulin molar ratio to values higher than 1.0 cause a significant decrease in the liver phosphorylase protein level.