Investigations of the molecular basis for the temperature-dependent insolubility of cryoglobulins. VI. Quenching by acrylamide of the intrinsic tryptophan fluorescence of cryoglobulin and non-cryoglobulin IgM proteins.
The acrylamide-quenching patterns of the intrinsic tryptophan fluorescence of six cold-soluble monoclonal immunoglobulin M (IgM) and two monoclonal IgM proteins possessing cryoglobulin properties (abnormal cold insolubility) have been compared. Static and dynamic components of quenching have been resolved by a modified form of the Stern-Volmer relationship. The unusual observation of static quenching seen with the multitryptophan containing IgM is determined to be a consequence of essentially homogeneous indole fluorescence arising from conserved tryptophan residues within each homologous immunoglobulin domain. Although the static component of the quenching of the two IgM cryoimmunoglobulins examined is similar to that of the non-cryoimmunoglobulin, IgM, some of the cryoglobulin's tryptophan residues appear to be more kinetically exposed to acrylamide than the tryptophans in the non-cryoglobulin IgM. An unusually large negative entropy of activation observed for the quenching process of both cryoimmunoglobulins suggests some abnormality in the dynamic (flexibility) properties of these proteins.