Isolation and properties of detergent-solubilized HLA antigens obtained from platelets

Deoxycholate-solubilized HLA antigens have been isolated from platelets and comprised a mixture of 43,000- and 39,000-dalton polypeptide chains associated with beta2-microglobulin. Limited proteolysis experiments suggested that the 39,000-dalton chain is a fragment of the intact 43,000-dalton chain. Further proteolysis of the 39,000-dalton fragment yields a 33,000-dalton component. The 39,000-dalton molecule is more acidic than both the 43,000- and the 33,000-dalton chains. Differences in the amino acid compositions of the 43,000- and 39,000-dalton species demonstrate that the peptide(s) released on generation of the 39,000-dalton component are charged. The proteolytic split most probably occurs in the COOH-terminal end, which, owing to its content of charged amino acids, most probably is not integrated into the hydrocarbon matrix of the membrane. The 39,000- and 43,000-dalton components bind detergent in micellar form and can be incorporated into liposomes. The 33,000-dalton fragment has lost the ability to bind detergent micelles and is not incorporated into liposomes.