Antigenic Properties of Native and Regenerated Horse Serum Albumin*$ by John O. Erickson

One of the characteristic manifestations of biological activity of proteins resides in their ability to elicit antibody formation. While the activity of certain immune bodies, as well as that of enzymes, or viruses, is known to be destroyed by processes causing protein denaturation, the relation between denaturation and antigenicity is only vaguely understood. I t has been reported that denaturation by heat (1-3), acid and alkali (4-7), ultraviolet irradiation (8, 9), or by controlled enzymatic action (10-12) alters the antigenic behavior of proteins. While earlier workers generally agreed that a denatured protein has both reduced antigenicity and altered serological specificity, more recent investigations of photo-oxidized egg albumin (13) and protein films (14) have indicated the possibility that certain kinds of denaturation may take place without any considerable alteration in specificity. The apparently conflicting evidence adduced in these studies may, at least in part, be ascribed to loose definition of the term denaturation. In a recent analysis of the problem, occurrence of intramolecular changes in a protein have been considered as the main criterion for denaturation (15), thereby excluding processes which result in reversible dissociation or aggregation of native protein molecules, or reactions with groups on the surface of protein molecules which leave their internal structure intact. Therefore, in order to correlate changes in immunological properties with effects of denaturation, as defined above, it is necessary: (1) to preclude the occurrence of changes in the nature of reactive chemical groupings on the surface of the protein molecule, which have been shown to be important in determining immunological specificity; (2) to carry out the denaturation process in a rigidly controlled fashion; and (3) to deal with proteins, well characterized in both native and denatured state. In preceding papers of this series (16) it was shown that if the process of denaturation of crystalline horse serum albumin by strong urea solutions is reversed, by dialyzing out the denaturing agent, a protein fraction is obtained