Inhibition of glycogen synthase (casein) kinase-1 by heparin.
Previous reports have shown that heparin is an inhibitor of casein kinase-2 (CK-2). It is unclear whether heparin is also an inhibitor of glycogen synthase (casein) kinase-1 (CK-1), a type 1 casein kinase. In this study it is shown that CK-1 is potently inhibited by heparin when phosvitin or calcineurin are used as substrates. With casein as a substrate, however, the kinase is insensitive to inhibition by heparin. Using phosvitin as a substrate half-maximal inhibition of CK-1 was observed with 0.14 microgram/ml heparin. Kinetic analyses indicate that at a constant concentration (0.10 mM) of ATP the Km of CK-1 for phosvitin is increased eightfold in the presence of 0.9 microgram/ml heparin; the Vmax is unchanged with or without heparin. At a constant concentration of phosvitin (4 mg/ml) heparin (0.9 microgram/ml) decreased the Vmax for ATP by 57%; the Km is unchanged with or without heparin. The inhibition of CK-1 by heparin can be reversed by KCl (greater than 100 mM). These results indicate that heparin is a potent inhibitor not only of CK-2 but also of CK-1. Hence heparin inhibition can no longer be arbitrarily used as a criterion to discriminate between these kinases.
Singh
T J
TJ
Department of Biology, University of Waterloo, Ontario, Canada.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D019703:Calcineurin; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D047388:Casein Kinases; D002364:Caseins / Q000378:metabolism; D002417:Cattle; D006493:Heparin / Q000494:pharmacology*; D007700:Kinetics; D009994:Osmolar Concentration; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D010774:Phosvitin / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism
D002148:Calmodulin-Binding Proteins; D002364:Caseins; D047428:Protein Kinase Inhibitors; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D006493:Heparin; D010774:Phosvitin; D011494:Protein Kinases; D047388:Casein Kinases; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases