SPECIES-SPECIFICITY OF HUMAN ANTI-BEEF, PORK INSULIN SERUM

Abstract

Crystalline pork, sheep, horse, beef (2 preparations) and beef desamido insulins and A and B chains of beef insulin were labeled with I131. The labeled insulin preparations were tested directly in reactions with insulin-binding antibodies in human anti-beef, pork insulin serums and were cross reacted in various combinations with unlabeled insulins of all species as well as with unlabeled human insulin. No differences were observed in the extent to which the 2 preparations of beef insulin-I131 and desamido beef insulin-I131 reacted with insulin-binding antibodies or in the degree to which each of the unlabeled beef preparations competed against the binding of one of the I131-labeled beef insulins. In general, beef and sheep insulins were bound more strongly than pork or horse insulins in both direct and cross reaction studies. These similarities are paralleled by known chemical similarities among the different animal species'' insulins. Human insulin cross reacted less strongly than did any of the animal insulins. The observed differences and similarities in binding of the various animal insulins suggest that the site of differences in amino acid sequence (residues 8 to 10 of the A chain) constitutes at least part of the antigenic site as well as of the site of reaction with the antibody.