Tyrosine phosphorylation and stimulation of protein kinase Cδ from porcine spleen by src in vitro

Abstract

Native protein kinase Cδ from porcine spleen is phosphorylated in vitro by the tyrosine kinase src and to a much smaller extent by fyn. The tyrosine phosphorylation of PKCδ is restricted to the activated state of the enzyme, i.e. it occurs only in the presence of an activator, such as TPA or bryostatin. Upon phosphorylation at tyrosine, the apparent molecular weight of PKCδ increases by 6 kDa. Phosphorylation by src induces a stimulation of PKCδ activity apparently exhibiting some substrate selectivity. Other PKC isoenzymes, such as cPKC (α,β,γ), are not phosphorylated by src or only to a very small extent. This phosphorylation is not dependent on TPA and does not cause an increase in activity and molecular weight of the enzyme.