The role of carbohydrate in the structure and function of nephritic factor.

Six nephritic factors (NeFs) were purified from the IgG fraction of sera of patients with PLD and/or MPGN by elution from EA C43bBb. All had at least one abnormal H chain component when examined by PAGE-SDS and two additionally had a large L chain. Four different H chains were found. Their apparent molecular weights and the frequency with which they occurred were: 65,000 (one NeF), 61,500 (four NeFs), 57,000 (two NeFs) and 55,000 (one NeF) compared with 53,500 daltons for normal H chain. The molecular weight of the large L chains was 26,500 daltons (cf. 23,500 for normal L chain). Both the NeF activity and the large components were located in the F(ab')2 fragment of the molecule and after reduction the large component was found in the Fd fragment of the H chain. Neuraminidase treatment of purified NeF caused a 1-2% decrease in apparent molecular weight of the large H chain on PAGE-SDS. Mild periodate oxidation, sufficient to cause primarily loss of carbohydrate, caused a marked loss of activity. Reduction and alkylation of NeF under neutral conditions caused only a small loss of activity but after acid dissociation the H and L chains were completely inactive.