Role of fructose in glycation and cross-linking of proteins.
Incubation of carbohydrate-free human serum albumin (HSA) with fructose in an aqueous buffer at pH 7.4 resulted in glycation of epsilon-amino groups of lysyl residues. A recently developed procedure, involving analysis of hexitol amino acids by high-performance liquid chromatography of phenylthiocarbamyl derivatives, was used to show that 85% of the bound hexose was attached to protein via carbon 2 (C-2). The remainder was attached to protein via carbon 1 (C-1). When incubations were conducted with glucose under identical conditions, all the hexose was attached via C-1. Examination of human ocular lens proteins showed that the majority of the covalently bound hexose was connected to epsilon-amino groups of lysyl residues via C-1; this was attributed mainly to nonenzymatic glucosylation in vivo, which has already been documented. A significant proportion (10-20%) of the bound hexose was connected via C-2. In view of the HSA-hexose incubation results (above), this indicated that the lens proteins had reacted with endogenous fructose; i.e., they had undergone nonenzymatic fructosylation in vivo. The model protein bovine pancreatic ribonuclease A reacted with fructose and glucose at similar rates under physiological conditions. However, covalent, non-disulfide cross-linking, which could be inhibited by D-penicillamine, was induced 10 times more rapidly by fructose than by glucose. It is postulated that some of the protein cross-linking that occurs in vivo is fructose-induced. The possible significance of these processes in diabetic subjects is discussed.
D003432:Cross-Linking Reagents; D003459:Crystallins / Q000378:metabolism*; D005632:Fructose / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D008239:Lysine; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D010396:Penicillamine / Q000494:pharmacology; D012709:Serum Albumin / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D003432:Cross-Linking Reagents; D003459:Crystallins; D012709:Serum Albumin; D005632:Fructose; D010396:Penicillamine; D008239:Lysine