Chemical studies of tissue polypeptide antigen (TPA). III. on the nature of the antigenic determinant(s) of TPA subfraction B1.

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 lysine, tyrosine, trytophan and arginine in subfraction B1 have been related to the change in the capacity of the antigen to bind to horse anti-HeLa serum. Complete although reversible loss of binding capacity resulted from blocking of arginine and a minor loss was noted upon modification of tyrosine. No measurable influence was noted upon modification of lysine or tryptophan. No cysteine has been detected in subfraction B1. Circular dichroism measurements show that TPA subfraction B1 is largely alpha-helical in solution, and that no correlation could be detected between antigenic activity and conformation.