Myristoylation of proteins in platelets occurs predominantly through thioester linkages

We have demonstrated by several lines of evidence that in platelets myristate is linked to proteins predominantly via thioester bonds as is palmitate, and the covalent binding of the two long chain saturated fatty acids to proteins involves the same mechanisms. The first piece of evidence to support the thioester linkage between myristate and proteins is that [³H]myristate could be removed from proteins via alkaline methanolysis, which disrupts ester bonds but not amide bonds. The second piece of evidence is that unlabeled palmitate, which can form only thioester bonds in physiologic concentrations, competitively inhibits the formation of alkaline methanolysis-sensitive covalent bonds between [³H]myristate and proteins. Third, by SDS-polyacrylamide gel electrophoresis and fluorography, the patterns of labeled proteins from [³H]myristate- and [³H]palmitate-labeled platelets are identical. Fourth, [³H]myristate-labeled proteins, like [³H]palmitate-labeled proteins, both release their fatty acid moieties when exposed to hydroxylamine at neutral pH, which disrupts thioester but not hydroxyester bonds. These findings indicate that although the covalent binding of palmitate to proteins was found to occur at a faster rate than that of myristate, protein S fatty acid acylation that occurs posttranslationally is not specific for palmitate.