Human monoclonal cryoimmunoglobulins. III. Analysis of thermodynamic properties of Jir (IgG3 kappa) protein by fluorescence polarization measurement.

In order to characterize the thermodynamic property of cryoimmunoglobulin which is related to the temperature-dependent solubility change in aqueous solution, the fluorescence polarization measurement of 1-dimethylaminonaphthalene-5-sulfonyl (DNS) conjugated cryoimmunoglobulin (Jir) and monoclonal immunoglobulins in various solvent conditions were comparatively carried out using the steady state excitation method by altering temperatures from nearly 10 to 40 degrees C, and the rotational relaxation times (rho h) for these molecules were calculated according to the Perrin-Weber's equation using the values of polarization (P). The results indicated that the rho h value of DNS-Jir (170 nsec) was almost twice that obtained by myeloma protein (90 nsec) belonging to the same subclass with Jir, but was considerably shorter than that obtained by a soluble immune complex with a molecular weight equivalent to Jir dimer. These results suggested that the molecular structure of Jir protein was thermodynamically less-flexible than that of the myeloma proteins, and that the restricted intra-molecular flexibility might be responsible for the unusual property of cryoimmunoglobulin.