Glucose autoxidation, a transition metal-catalyzed process generating H₂O₂ and ketoaldehydes, contributes to protein modification by glucose in vitro. The metal-chelating agent DETAPAC, which inhibits glucose autoxidation, also reduces the covalent attachment of glucose to bovine serum albumin (BSA). A maximal 45% inhibition of covalent attachment was observed, but this varied with glucose and DETAPAC concentrations, suggesting at least two modes of attachment. The extent of inhibition of the metal-catalyzed pathway correlated with the extent of inhibition of glycosylation-associated chromo- and fluorophore development. DETAPAC also inhibited tryptophan fluorescence quenching associated with glycosylation. Conversely, ketoaldehydes generated by ⁶⁰Co irradiation bound avidly to albumin and accelerated browning reactions. These findings suggest that a component of protein glycosylation is dependent upon glucose autoxidation and subsequent covalent attachment of ketoaldehydes. The process of glucose autoxidation or ketoaldehydes derived therefrom appears to be important in chromophoric and fluorophoric alterations. The chemical evidence for the 'Amadori' product derived from glucose-protein reactions is consistent with the structure expected for the attachment of a glucose-derived ketoaldehyde to protein. The concept of 'autoxidative glycosylation' is discussed in relation to oxidative stress in diabetes mellitus. Hyperglycaemia, a primary clinical manifestation of diabetes, is associated with the development of diabetic complications. Various cytotoxic roles for glucose have been proposed, including nonenzymic glycosylation of proteins, which produces new protein-bound chromo- and fluorophores and may lead to protein conformational and functional alterations. The significance of this process to human diabetes is not clear, but the extent of tissue browning has been correlated with the incidence and severity of complications in human diabetics. Monosaccharides can enolize and reduce molecular oxygen under physiological conditions, yielding α-ketoaldehydes, H₂O₂, and free radical intermediates. The occurrence of this process in vivo could contribute to elevated levels of plasma peroxides in diabetics and may contribute to protein modification reactions performed with glucose in vitro. Such studies involve long-term incubation of protein with glucose followed by investigation of structural or functional alterations. It is conceivable that glucose autoxidation might contribute to monosaccharide attachment, chromophore development, and protein oxidative damage. The extent of nonenzymic glycosylation could be a reflection of cumulative oxidative stress. The present study assessed the contribution of glucose autoxidation to protein glycosylation and associated chromophoric and fluorophoric alterations.Glucose autoxidation, a transition metal-catalyzed process generating H₂O₂ and ketoaldehydes, contributes to protein modification by glucose in vitro. The metal-chelating agent DETAPAC, which inhibits glucose autoxidation, also reduces the covalent attachment of glucose to bovine serum albumin (BSA). A maximal 45% inhibition of covalent attachment was observed, but this varied with glucose and DETAPAC concentrations, suggesting at least two modes of attachment. The extent of inhibition of the metal-catalyzed pathway correlated with the extent of inhibition of glycosylation-associated chromo- and fluorophore development. DETAPAC also inhibited tryptophan fluorescence quenching associated with glycosylation. Conversely, ketoaldehydes generated by ⁶⁰Co irradiation bound avidly to albumin and accelerated browning reactions. These findings suggest that a component of protein glycosylation is dependent upon glucose autoxidation and subsequent covalent attachment of ketoaldehydes. The process of glucose autoxidation or ketoaldehydes derived therefrom appears to be important in chromophoric and fluorophoric alterations. The chemical evidence for the 'Amadori' product derived from glucose-protein reactions is consistent with the structure expected for the attachment of a glucose-derived ketoaldehyde to protein. The concept of 'autoxidative glycosylation' is discussed in relation to oxidative stress in diabetes mellitus. Hyperglycaemia, a primary clinical manifestation of diabetes, is associated with the development of diabetic complications. Various cytotoxic roles for glucose have been proposed, including nonenzymic glycosylation of proteins, which produces new protein-bound chromo- and fluorophores and may lead to protein conformational and functional alterations. The significance of this process to human diabetes is not clear, but the extent of tissue browning has been correlated with the incidence and severity of complications in human diabetics. Monosaccharides can enolize and reduce molecular oxygen under physiological conditions, yielding α-ketoaldehydes, H₂O₂, and free radical intermediates. The occurrence of this process in vivo could contribute to elevated levels of plasma peroxides in diabetics and may contribute to protein modification reactions performed with glucose in vitro. Such studies involve long-term incubation of protein with glucose followed by investigation of structural or functional alterations. It is conceivable that glucose autoxidation might contribute to monosaccharide attachment, chromophore development, and protein oxidative damage. The extent of nonenzymic glycosylation could be a reflection of cumulative oxidative stress. The present study assessed the contribution of glucose autoxidation to protein glycosylation and associated chromophoric and fluorophoric alterations.