Kinetics of the precipitation of cryoimmunoglobulins

The kinetics of the cryoprecipitation of two monoclonal IgG and two monoclonal IgM cryoimmunoglobulins, two IgM/IgG mixed cryoglobulins and a series of cold soluble monoclonal IgG and IgM immunoglobulins in the presence of polyethylene glycol have been compared by time dependent turbidity measurements. The effects of temp and ionic strength on kinetic processes are described in detail. The monoclonal cryoimmunoglobulins display lag times which are not seen with the other proteins, suggesting a critical nucleation event. The protein concn dependence of the lag times indicate that these nucleation centers contain only a few immunoglobulin molecules. Direct evidence for the existence of precipitation nuclei was obtained from dynamic light scattering studies of two of the monoclonal proteins during their lag periods. Both proteins manifested an approx. 20% decrease in their mean diffusion coefficients (corresponding to a 25% increase in Stokes' radius) prior to detectable precipitation. This suggests the formation of nuclei between 2 and 8 times the size of the monomeric proteins. It is postulated that the increasing size of mixed cryoglobulin complexes with decreasing temp provides analogous nucleation sites. The latter stages of precipitation appear to be kinetically similar for all proteins examined, although the size and shape of the aggregates are quite variable.