An immunologic approach to the conformational equilibria of polypeptides.

Antibodies reactive with distinct regions of the staphylococcal nuclease molecule were prepared both by immunization with polypeptide fragments of nuclease and by immunization with intact nuclease followed by fractionation of the antiserum on immuno-absorbent columns bearing the corresponding fragments. Comparisons of the interactions of these antibody preparations with nuclease, by quantitative precipitin assays and enzyme inhibition studies, showed marked differences attributable to the conformation of the immunizing antigens. An interpretive model is proposed in which antibodies fractionated from anti-nuclease serum react effectively only with the "native format determinants" of polypeptide fragments of nuclease. It is postulated that such determinants are generated in polypeptide fragments by spontaneous and reversible folding of the polypeptide chain. The model permits experimental determination of parameters, K(conf), for the proposed conformational equilibria.