Cation-independent mannose 6-phosphate receptor contains covalently bound fatty acid

The cation-independent mannose 6-phosphate receptor (215,000 daltons) was isolated from embryonic bovine tracheal cells and embryonic human skin fibroblasts labelled with 3H]palmitic acid. The tritium label was detected in the protein upon fluorographic analysis of SDS-polyacrylamide gels of the purified receptor. The label was not sensitive to hydroxylamine, methanolic KOH, or beta-mercaptoethanol, but labelled fatty acid was recovered from the protein by acidic methanolysis. Labelled receptor protein could not be isolated from cells grown in the presence of 3H]myristic acid. The results suggest the presence of amide-linked palmitic acid in the structure of the cation-independent mannose 6-phosphate receptor.