A study of the carbohydrate present in three type K macroglobulins.

Abstract

For a monomeric molecular weight of 180000 three type K macroglobulins (IgM) contained 6-deoxygalactose, mannose, galactose, 2-acetamido-2-deoxyglucose and N-acetylneuraminic acid in the molar proportions 5:38:11:27:7 for Row IgM, 5:31:9:21:7 for Sha IgM, and 5:29:11:26:8 for Tya IgM. The first two proteins were euglobulins whereas Tya IgM was a pseudoglobulin, and therefore the total content of carbohydrate does not appear to be related to the physicochemical properties of the proteins. The three proteins appeared to contain different numbers of oligosaccharide units, Row IgM having about ten units/monomer, and Sha IgM and Tya IgM about eight each. All three proteins had two types of oligosaccharide unit, which by analogy with an immunoglobulin A myeloma globulin were called Type 2 and Type 3 respectively. The Type 2 units had molecular weights equal to or greater than 2000 and contained 1 residue of 6-deoxygalactose, 3-4 of mannose, 1-2 of galactose, 3-4 of 2-acetamido-2-deoxyglucose and 0-2 of N-acetylneuraminic acid. The Type 3 units had molecular weights of less than 2000 and contained 0-1 residue of 6-deoxygalactose, 3-6 of mannose, 0-1 of galactose, 1-3 of 2-acetamido-2-deoxyglucose and no N-acetylneuraminic acid. Glycopeptides corresponding to the two types of unit varied in their aspartic acid content in that most of the Type 3 glycopeptides possessed only 1 residue of aspartic acid whereas most of the Type 2 glycopeptides had an average content greater than 1 residue.