Partial purification of detergent-soluble HL-A antigen and its cleavage by papain

HL-A antigen solubilized with the non-ionic detergent, Brij 99, has been purified to about 50% of homogeneity from a cultured human lymphoblast line. It consists of two nonidentical subunits of 44,000 and 12,000 molecular weight (MW). Upon papain proteolysis the 44,000 MW peptide is converted by at least two cleavages to a 34,000 MW peptide, but the 12,000 MW peptide appears to be unchanged. Concomitantly, the apparent molecular weight in gel filtration chromatography under nondenaturing conditions in the presence of Brij 99 is reduced from 460,000 to 45,000. HL-A molecules produced by direct papain proteolysis of membranes and by papain treatment of purified detergent-soluble HL-A are identical.