Activation of a manganese-dependent membrane protein kinase by serine and tyrosine phosphorylation.
A Mn2(+)-dependent serine/threonine protein kinase from rat liver membranes copurifies with the insulin receptor (IR) on wheat germ agglutinin (WGA)-sepharose. The kinase is present in a nonactivated form in membranes but can be activated 20-fold by phosphorylating the WGA-sepharose fraction with casein kinase-1 (CK-1), casein kinase-2 (CK-2), or casein kinase-3 (CK-3). The activated kinase can use IR beta-subunit, myelin basic protein, and histones as substrates. Activation of the kinase seems to proceed by two or more steps. Sodium vanadate and Mn2+ are required in reaction mixtures for activation to be observed, whereas the tyrosine kinase-specific substrate, poly (glu, tyr), completely inhibits activation. These observations suggest that, in addition to serine/threonine phosphorylation by one of the casein kinases, activation of the Mn2(+)-dependent protein kinase also requires tyrosine phosphorylation. Such phosphorylation may be catalyzed by the IR tyrosine kinase.
Department of Biology, University of Waterloo, Ontario, Canada.
T J
TJ
Singh
D000818:Animals; D047388:Casein Kinases; D004789:Enzyme Activation; D066298:In Vitro Techniques; D008345:Manganese / Q000378:metabolism; D004676:Myelin Basic Protein / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*
D004676:Myelin Basic Protein; D010769:Phosphothreonine; D010768:Phosphoserine; D008345:Manganese; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D047388:Casein Kinases