The physicochemical properties and the process of pyrogel formation of IgD pyroglobulin.

The extremely rare IgD pyroglobulin caused opalescence, lost its antigenicity and acquired more negative charge when heated for 30 min at 56 degrees C. Exposure to 60 degrees C for 60 min produced a firm gel. The thermoprecipitability was abolished by the treatment with guanidine, urea and sodium dodecyl sulfate, but not by 2-mercaptoethanol or neuraminidase, and required the presence of both heavy and light chains. However, amino acid analysis showed abnormalities only in the heavy chain. We hypothesize that the irreversible heat-induced aggregation of IgD pyroglobulin is the result of a conformational change, triggered by light chain, which increases the molecular hydrophobicity.