Sensitivity to reduction of human immunoglobulin G of different heavy chain sub-classes

Abstract

Human IgG proteins of all four heavy chain sub-classes were reduced over a range of dithioerythritol concentrations, and the products were examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. With the exception of IgG 3, unless the samples were boiled in 2% (w/v) sodium dodecyl sulphate-0.075 M iodoacetamide prior to electrophoresis, problems arose as a result of aggregation. Reduction intermediates formed from IgG 1, IgG 2 and IgG 3 were H 2L, H 2 and HL. With IgG 4 the predominant intermediate was the HL subunit. In IgG 4, therefore, the interheavy chain disulphide linkage is more sensitive to reduction than the heavy-light chain bridge, while in the other subclasses the interchain bonds are randomly reduced. These differences can be used in association with the well known papain-sensitivity differences of the sub-classes for the chemical typing of IgG monoclonal proteins, and may correlate with a different biosynthetic pathway for IgG 4.