Palmitoylation of platelet proteins

Palmitoylation as incorporation of [(3)H] palmitic acid into proteins occurred in platelets as in other cell systems. The linkage of palmitic acid to platelet proteins was stable to SDS and organic solvents but was sensitive to hydroxylamine, consistent with oxyester or thioester bond(s). Non-reduced SDS PAGE analysis revealed that the most prominantly labelled proteins were a quadruplet of proteins of 30-38 kDa. Under reducing conditions, these proteins appeared as a doublet of 38 kDa proteins. Thrombin or PMA enhanced the incorporation of label into these proteins, suggesting the involvement of palmitoylation in platelet activation. In prelabelled platelets, A23187 led to a E-64d-sensitive decrease of label associated with a 35 kDa protein while PMA caused a stuarosporine-sensitive shift of the same protein in a non-reduced gel. Some of the palmitoylated proteins were associated with the cytoskeleton. Thrombin appeared to have different effects on these labelled cytoskeletal proteins. While the identity of most of the palmitoylated platelet proteins remains unknown, a few palmitoylated proteins have been identified to be CD9, glycoproteins IIIa, Ib and IX.