Palmitoylation of ocular lens membrane proteins.

Covalent attachment of fatty acids to proteins may be a means of anchoring cytoplasmic proteins to the plasma membrane. The possibility that lens membrane proteins can be fatty acid acylated was studied by incubating the lenses of young rats with 9,10-3H-palmitate. The distribution of 3H-palmitate among the lens membrane polypeptides separated by electrophoresis was determined by fluorography and by direct measurement of radiolabel in sliced gels. 3H-palmitate was found to be incorporated into membrane polypeptide fractions of approximately 19, 30, and 35 kD; the 30 kD fraction appeared to be most highly labeled. The principal lens membrane protein, the main intrinsic protein (MIP 26), was not labeled. This incorporation appeared to be due to covalent attachment rather than to noncovalent binding, and was temperature dependent, independent of protein synthesis, and resistant to displacement by beta-mercaptoethanol. Whether the acylation is enzymatic or nonenzymatic is unclear. The identity of the acylated polpeptides is unknown.