Chemical Studies of Tissue Polypeptide Antigen (TPA). III. On the Nature of the Antigenic Determinant(s) of TPA Subfraction B1.

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Abstract
Tissue polypeptide antigen (TPA) which is a protein isolated from, e.g., human carcinoma cells, has previously been separated into subfractions and studied with biochemical methods. Gel diffusion studies show that the antigenic determinants are retained through the isolation and purification procedures. Specific modifications of the amino acid residues Lys, Tyr, Try and Arg in subfraction B1 were related to the change in the capacity of the antigen to bind to horse anti-[human cervical carcinoma cells]HeLa serum. Complete, although reversible, loss of binding capacity resulted from blocking of Arg, a minor loss was noted upon modification of Tyr. No measurable influence was noted upon modification of lysine or Try. No Cys was detected in subfraction B1. Circular dichroism measurements show that TPA subfraction B1 is largely .alpha.-helical in solution; no correlation was detected between antigenic activity and conformation.