Zn2+ enhances protein tyrosine kinase activity of human platelet membranes

Abstract In human platelet membranes enhanced tyrosine phosphorylation of certain proteins was observed when Zn 2+ instead of Mg 2+ or Mn 2+ was used as a divalent cation for the kinase reaction. An enhanced level of phosphate incorporation into tyrosine residues occurred into a 68 kDa polypeptide besides the 45 kDa and 105 kDa proteins. Preincubation of platelet membranes with TBR-IgG showed a concentration-dependent inhibition of the phosphorylation of the 45, 68 and 105 kDa proteins. Moreover, pp60 c-src , representing the major protein tyrosine kinase activity in platelets, was found to be stimulated by Zn 2+ . The data, thus, support the assumption that pp60 c-src kinase is responsible for Zn 2+ stimulated tyrosine phosphorylation.