Isolation and characterization of fragments of human serum albumin containing some of the antigenic sites of the whole molecule

Abstract

In an investigation of the structural features that constitute an antigenic site in bovine serum albumin, Porter (1957) isolated a fragment of molecular weight 12 000 which retained the power to combine with the specific rabbit antiserum. Attempts to split this piece further, without loss of activity, were unsuccessful, and with material of this size it seemed probable that detailed chemical investigation to locate the combining site would give equivocal results. Lapresle and colleagues (Lapresle, 1955; Lapresle, Kaminski & Tanner, 1959; Lapresle & Webb, 1960) have shown that the antigenic activity of human serum albumin will survive digestion with rabbit-spleen extracts and other enzymes. The partial hydrolysis of this protein under conditions similar to those used for bovine serum albumin (i.e. continuous digestion with chymotrypsin in a dialysis sac) was therefore studied. In preliminary work (A. Holasek & R. R. Porter, unpublished work) it appeared that active fragments of molecular weight substantially less than 12 000 could be produced. More detailed in- vestigation has shown that a variety of such pieces are produced from human albumin and that their molecular weights range from 7100 to 23 400. Some precipitate and some combine with but do not precipitate the rabbit antiserum. The isola- tion and properties of four of these active pieces will be described.