Zn2+ enhances protein tyrosine kinase activity of human platelet membranes

Abstract
In human platelet membranes enhanced tyrosine phosphorylation of certain proteins was observed when Zn2+ instead of Mg2+ or Mn2+ 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, pp60c‐src, representing the major protein tyrosine kinase activity in platelets, was found to be stimulated by Zn2+. The data, thus, support the assumption that pp60c‐src kinase is responsible for Zn2+ stimulated tyrosine phosphorylation.