title: Role of protein kinase C in the regulation of rat liver glycogen synthase.
abstract: Rat liver glycogen synthase was phosphorylated by purified protein kinase C in a Ca2+- and phospholipid-dependent fashion to 1-1.4 mol PO4/subunit. Analysis of the 32P-labeled tryptic peptides derived from the phosphorylated synthase by isoelectric focusing and two-dimensional peptide mapping revealed the presence of a major radioactive peptide. The sites in liver synthase phosphorylated by protein kinase C appears to be different from those phosphorylated by other kinases. Prior phosphorylation of the synthase by protein kinase C has no significant effect on the subsequent phosphorylation by glycogen synthase (casein) kinase-1 or kinase Fa, but prevents the synthase from further phosphorylation by cAMP-dependent protein kinase, Ca2+/calmodulin-dependent protein kinase, phosphorylase kinase, or casein kinase-2. Additive phosphorylation of liver glycogen synthase can be observed by the combination of protein kinase C with the former set of kinases but not with the latter. Phosphorylation of liver synthase by protein kinase C alone did not cause an inactivation nor did the combination of this kinase with glycogen synthase (casein) kinase-1 or kinase Fa produce a synergistic effect on the inactivation of the synthase. Based on these findings we conclude that the phorbol ester-induced inactivation of glycogen synthase previously observed in hepatocytes cannot be accounted for entirely by the activation of protein kinase C.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin / Q000494:pharmacology; D047388:Casein Kinases; D003488:Cyanogen Bromide; D000242:Cyclic AMP / Q000494:pharmacology; D006006:Glycogen Synthase / Q000378:metabolism*; D007525:Isoelectric Focusing; D008099:Liver / Q000201:enzymology*; D009132:Muscles / Q000201:enzymology; D010446:Peptide Fragments / Q000378:metabolism; D010743:Phospholipids / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D014357:Trypsin
chemical_list: D002147:Calmodulin; D010446:Peptide Fragments; D010743:Phospholipids; D000242:Cyclic AMP; D006006:Glycogen Synthase; D011494:Protein Kinases; D047388:Casein Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D014357:Trypsin; D003488:Cyanogen Bromide; D002118:Calcium