Isolation of IgG3 from normal human sera and from a patient with multiple myeloma by using protein A-sepharose 4B.

Affinity chromatography of IgG on protein A-Sepharose was used to isolate the human subclass IgG3 from normal serum and from a patient with multiple myeloma. The isolated material was purified by chromatography on Sephadex G-150 and characterized immunochemically. Ultracentrifugation studies gave so20,w values of about 6.80 for both normal and myeloma IgG3. Approximately 54 half-cystine residues per molecule of IgG3 were obtained as judged from amino acid analysis after performic acid oxidation of the proteins. Polyacrylamide gel electrophoresis in 0.1% sodium dodecyl sulfate of the isolated and reduced material resulted in two bands corresponding to molecular weights of approximately 23,000 and 56,000, respectively. The yield of normal human IgG3 represented 1%-2% of the total IgG.