Structural studies on an IgM-lambda pyroglobulin.

An IgM-lambda pyroglobulin from a patient with Waldenström's syndrome was studied. Heavy and light chains were separated and their N-terminal amino acid sequence determined. The heavy chain was unblocked and belonged to the VHIII subclass, and the light chain belonged to the lambda I subclass. Factors influencing pyroprecipitability were examined through experiments designed to study some of the physical and chemical properties of an IgM-lambda pyroglobulin. Pyroprecipitability was affected by pH, ionic strength, urea, and reducing agents, suggesting an involvement of noncovalent electrostatic interactions. It was also demonstrated through recombinant experiments that it is necessary to have covalently joined homologous heavy and light chains in pentameric form for pyroprecipitation to occur. Since neither heavy nor light chains had any unique structural features, the reasons for this property remain obscure but may reflect the result of conformational factors.