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Studies of Maleylated Chains of Human IgM¹

From the Division of Clinical Immunology and Rheumatology, Department of Medicine and Departments of Microbiology and Biochemistry, University of Alabama in Birmingham, The Medical Center, Birmingham, Alabama 35233

Abstract

An approach to the isolation and physicochemical study of the chains of IgM is presented. The chains were separated after mild reduction in the absence of guanidine as the maleylated derivatives. The maleylated µ and chains were isolated in pure form with their intrachain disulfide bonds intact by gel filtration on Sephadex G-200 in Tris-glycine buffer, pH 8.9. Disulfide bond titration of these modified chains revealed 17 such bonds per 7S IgM subunit (5 interchain + 8 intrachain per 2 µ + 4 intrachain per 2 ). These findings agreed well with the finding of 18 disulfides per subunit obtained on reduction of 19S IgM for 6 hr in 3M guanidine. The maleylated chains were soluble permitting the determination of the molecular weight from the sedimentation and diffusion coefficients in the absence of denaturing agent. The molecular weight determined from these values for the maleylated µ chain was 80,000 and that for the maleylated chain was 23,000. Based on the number of maleyl groups on the respective chains, the molecular weight of unmodified µ chain was 75,000 and that of unmodified chain was 22,000.

Footnotes

¹ This work was supported by grants from National Institutes of Health and the John A. Hartford Foundation, Inc., of New York.

² John and Mary R. Markle Scholar in Academic Medicine and Research. Career Development Awardee (K3 GM 25386).