CARBOHYDRATE CONTENT OF NORMAL 19 S GLOBULINS

CHEMICAL CHARACTERIZATION OF GLYCOPEPTIDES FROM HUMAN gammaM-GLOBULINS

A survey of human pathological macroglobulins revealed that γM can be divided into at least two groups on the basis of carbohydrate composition. Differences between the two groups exist in the total percentage of carbohydrate (10.69 ± 1.49% for group 1, 7.71 ± 0.65% for group II) which is attributable to variation in hexose content. Glycopeptides from macroglobulins of each group were purified from pronase digests and characterized chemically. Macroglobulins from each group contain three types of oligosaccharides. Glycopeptide I for each group consisted of mannose, galactose, and NAG with a ratio of 3:2:1 for group I and a ratio of 2:1:2 for group II. Glycopeptide II consisted of mannose, galactose, and NAG (9:1:2) for group I, and mannose, fucose, galactose, and NAG (2:1:3:2) for group II. Glycopeptide III in both groups consisted of mannose, fucose, galactose, NAG, and sialic acid with a ratio of 6:2.5:2.5:5.5:2 for group I and a ratio of 5:1:1:6:1 for group II. Molecular weight estimations by gel filtration indicates that there are 10 glycopeptides I and II and 20 units of glycopeptide III per molecule of γM.

PREPARATION AND PROPERTIES OF THE PEPTIDE CHAINS OF NORMAL HUMAN 19 S GAMMA-GLOBULIN (IGM)

1. A method is described for preparing pure samples of 19s gamma-globulin (IgM) from normal human serum by using successive steps of dialysis, density-gradient ultracentrifugation, chromatography on DEAE-cellulose, and gel filtration on Sephadex G-200. The yield of IgM (20-25mg./100ml. of serum) was equivalent to about one-quarter of that present in normal serum. 2. Analysis of the separated peptide chains of normal IgM and IgG (7s gamma-globulin) showed considerable differences in the amino acid composition of A chains from the two proteins; their respective B chains, on the other hand, were similar in composition. The carbohydrate of both proteins is confined almost entirely to the A chains; the IgM A chain contains about four times as much carbohydrate as the IgG A chain. 3. These findings support the view that the different classes of human immunoglobulin have B chains that are identical and A chains that are chemically distinct.