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The role of histidine residues in the nonenzymic covalent attachment of glucose and ascorbic acid to protein.

Copper ions have been suggested to play a role in the non-covalent glycosylation (glycation) of proteins via transition metal-catalysed oxidations. We have further investigated "autoxidative glycosylation" by comparison of the behaviour of dog and bovine serum albumin with respect to the oxidative reactions of glucose and ascorbate. The proteins possess similar numbers of total amino residues available for glucose attachment but dog serum albumin contains fewer histidine groups and also lacks a high affinity copper-binding site. We find that the higher copper-binding capacity of bovine serum albumin is reflected in a lower rate of ascorbate oxidation as well as less protein oxidative damage than is the case for dog serum albumin. We also observe that modification of bovine serum albumin histidine groups by diethylpyrocarbonate enhances ascorbate-mediated protein fluorophore formation.