Influence of heat on the conformational stability of a human IgG cryoglobulin

Temperature-induced conformational changes of a human immunoglobulin G cryoglobulin (cryoIgG) (IgG) (gamma 1:lambda, Gm4) was investigated and compared with a human myeloma IgG (gamma 1:lambda, Gm4) employing spectrofluorimetric and immunochemical methods. Fluorescence measurements revealed the major changes in protein conformation of both proteins at a temperature of 62 degrees C and above, the measurements being carried out with excitation wavelengths at 278 and 295 nm, respectively. Studies on both cryoIgG and myeloma IgG, which were heat denatured at high temperatures and subsequently cooled at 25 degress C, indicated that both proteins underwent progressively irreversible conformational changes beyond 65 degress C and cryoIgG appeared to be more temperature sensitive than myeloma IgG. Evaluation of the changes on specific antigenic determinant sites using antigen-antibody interaction revealed that the Fc determinant sites of both the proteins were disorganized to a greater extent at a temperture of 68 degress C than Fd or lambda-chain antigenic determinant sites. The Fd determinant sites of myeloma IgG were, however, found to be more heat labile than those of cryoIgG.