Isolation and Properties of Detergent‐Solubilized HLA Antigens Obtained from Platelets

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Abstract
Deoxycholate-solubilized HLA antigens were isolated from platelets and comprised a mixture of 43,000 and 39,000 dalton polypeptide chains associated with .beta.2-microglobulin. Limited proteolysis experiments suggested that the 39,000 dalton chain was a fragment of the intact 43,000 dalton chain. Further proteolysis of the 39,000 dalton fragment yielded a 33,000 dalton component. The 39,000 dalton molecule was more acidic than the 43,000 and the 33,000 dalton chains. Differences in the amino acid compositions of the 43,000 and 39,000 dalton species demonstrated that the peptide(s) released on generation of the 39,000 dalton component were charged. The proteolytic split most probably occurred in the COOH-terminal end, which, due to its content of charged amino acids, probably was not integrated into the hydrocarbon matrix of the membrane. The 39,000 and 43,000 dalton components bound detergent in micellar form and could be incorporated into liposomes. The 33,000 dalton fragment lost the ability to bind detergent micelles and was not incorporated into liposomes.