Isolation and identification of the Cmicron4-domain of IgM

Intact Cmicron4-domain was isolated by molecular exclusion chromatography of reduced and alkylated Fc5 micron prepared by tryptic digestion at 60 degrees C of a monoclonal IgM. Two fragments were obtained of which one contained carbohydrate and the other none. These fragments were successfully separated by chromatography on insolubilised Concanavalin A. Cmicron4-domain was identified by means of amino acid sequence, amino acid composition, molecular weight and immunological analyses. It has a molecular weight of 14,700 daltons and results from tryptic cleavage at Lys-445 of the micron-chain.