Isolation and Characterization of the Immune Macroglobulin from the Paddlefish, Polyodon spathula

Abstract

Abstract The immune macroglobulin from the paddlefish, Polyodon spathula, was purified and characterized physicochemically. The macroglobulin had a sedimentation coefficient of 14.2 S and a molecular weight of 660,000. Total reduction and alkylation in 7 m guanidine hydrochloride resulted in dissociation into heavy (H) and light (L) chains. The H and L chains were separated by gel filtration and found to have molecular weights of 58,100 and 21,000, respectively, employing sedimentation equilibrium in 5.0 m guanidine hydrochloride. Based on absorbance, equimolar quantities of the chains were recovered from the macroglobulin. These data are compatible with previously reported electron microscopic studies (Acton, R. T., Weinheimer, P. F., Dupree, H. K., Russell, T. R., Wolcott, M., Evans, E. E., Schrohenloher, R. E., and Bennett, J. C., Proc. Nat. Acad. Sci. U. S. A., 68, 107 (1971)), which demonstrated a tetrameric structure for the immune macroglobulin, and indicated that the structural subunit consists of two H and two L chains. Generally the amino acid composition was similar to mammalian IgM H and L chains. Although no NH2-terminal group was detected in the light chain, the sequence of the first 5 residues from the NH2-terminus of the H chain was found to be [see PDF for sequence]. These data provide additional evidence for a structural similarity among phylogenetically distinct immune macroglobulins and suggest a common evolutionary origin.