Biological and physical properties of a human m-cryoglobulin and its monomer subunit.

A patient with Waldenstrom's macroglobulinaemia was found to have a serum cryoprecipitate which consisted entirely of a γMK-macroglobulin. This protein had no detectable antibody activity against a variety of other serum components and fixed only minimal amounts of complement over temperatures ranging from 4°C to 37°C. Precipitation of the cryoglobulin began at about 30°C and was complete at temperatures below 20°C. In contrast to other macroglobulins that have been reported, cryoprecipitability persisted after the protein was dissociated into its monomer subunits. Isolated subunits formed cryoprecipitates as did the hybrid macroglobulin formed from equal parts of such subunits and the subunits of a non-cryoprecipitating macroglobulin. Carbohydrate content of the cryoglobulin was 12·81%, a value similar to γM molecules in general. Enzymatic removal of a portion of the carbohydrate caused the protein to become insoluble at even higher temperatures. A single type of intermolecular binding responsible for cryoprecipitation could not be defined. Addition of salt or non-polar solvent, or change in pH had little effect on cryoprecipitability at 4°C, but all of these measures did cause an increased solubility at 24°C, a transitional temperature for cryoprecipitability. Addition of a variety of serum proteins and glycine also served to increase protein solubility. These data suggest that cryoprecipitation may involve both hydrophobic and electrostatic bonds. Temperature induced changes in molecular configuration might also indirectly influence cryoprecipitation by altering the binding site.