Is Antibody-Globulin “Denatured” by Its Combination with Antigen?

It has frequently been stated that antibody becomes “denatured” when combined with its antigenic or haptenic counterpart. “Denatured” is one of our slippery words which has a loose rather than a definitive signification. Perhaps “lessened solubility” most commonly expresses what is meant by denaturation. Shibley 1 has recorded the remarkably identical electrophoretic behavior of thermally denatured normal globulin and of bacteria thoroughly coated with antibody-globulin. But, that antibody-globulin has not really lost its natural (and very labile) qualities as a result of its combination with antigen, is shown by the facts that dissociated antibody retains its specific combining characteristics, and immune sera produced by injecting antibody-antigen complexes not only reflect the species-specificity of the serum, 2 but also the particular features of different kinds of antibody, e. g., that of antipneumococcal serum is antigenically somewhat different from diphtheric antitoxin 3 — each having been combined with its antigen before injection into the antibody-producing animal.

To compare, in another way, the properties of specific globulin-antigen compounds and thermally denatured globulin we have mixed an opalescent solution of the latter (normal rabbit's serum, diluted with 3 volumes of water, steamed for 15 minutes, and centrifuged) with specific precipitative systems (hemocyanin and ovalbumin) and have found that the amounts of precipitated nitrogen were no greater than those produced in mixtures not containing the heated normal serum whether in the zone of equivalence, of excessive antigen, or of excessive antibody. In these respective zones the comparative figures, averages from duplicate analyses, were 0.512 and 0.489; 0.517 and 0.509; 0.402 and 0.408 mg. N in the Fulgur carica hemocyanin-system; 0.103 and 0.110; 0.106 and 0.117; 0.172 and 0.181 mg. N in the Limulus polyphemus-system. Mixtures of ovalbumin and its antiserum (rabbit) were made only in the zone of equivalence and of excessive antibody. The nitrogens in the precipitates were 0.743 and 0.749; 0.498 and 0.502 mg.