Effect of nonenzymatic glycation on the structure of immunoglobulin G

Incubation of human immunoglobulin G with glucose in vitro leads to covalent incorporation of the sugar concomitant with marked changes in molecular structure. After six to ten days of glucose incubation, absorption at 350 nm and fluorescence at 440 nm upon excitation at 370 nm markedly increased, indicating formation of nonenzymatic browning products. Furthermore, immunoglobulin G derivatives of a molecular mass of 500,000 Da appeared during glucose incubation as revealed by gel filtration. Electrophoretic examination of the 500-kDa protein revealed the formation of covalently bound immunoglobulin G polymers. Compared with nonglycated monomeric immunoglobulin G, functional properties of the 500-kDa protein, such as binding of protein A and fixation of complement are markedly reduced.