Reaction of ascorbate with lysine and protein under autoxidizing conditions: formation of N.epsilon.-(carboxymethyl)lysine by reaction between lysine and products of autoxidation of ascorbate

Abstract

N epsilon-(Carboxymethyl)lysine (CML) has been identified as a product of oxidation of glucose adducts to protein in vitro and has been detected in human tissue proteins and urine [Ahmed, M. U., Thorpe, S. R., & Baynes, J. W. (1986) J. Biol. Chem. 261, 4889-4894; Dunn, J. A., Patrick, J. S., Thorpe, S. R., & Baynes, J. W. (1989) Biochemistry 28, 9464-9468]. In the present study we show that CML is also formed in reactions between ascorbate and lysine residues in model compounds and protein in vitro. The formation of CML from ascorbate and lysine proceeds spontaneously at physiological pH and temperature under air. Kinetic studies indicate that oxidation of ascorbic acid to dehydroascorbate is required. Threose and N epsilon-threuloselysine, the Amadori adduct of threose to lysine, were identified in the ascorbate reaction mixtures, suggesting that CML was formed by oxidative cleavage of N epsilon-threuloselysine. Support for this mechanism was obtained by identifying CML as a product of reaction between threose and lysine and by analysis of the relative rates of formation of threuloselysine and CML in reactions of ascorbate or threose with lysine. The detection of CML as a product of reaction of ascorbate and threose with lysine suggests that other sugars, in addition to glucose, may be sources of CML in proteins in vivo. The proposed mechanism for formation of CML from ascorbate is an example of autoxidative glycosylation of protein and suggests that CML may also be an indicator of autoxidative glycosylation of proteins in vivo.

Ascorbic acid can either increase or decrease low density lipoprotein modification

“…In addition, adding the antioxidant BHT together with the ascorbate prevented the increase in TBARS and the enhanced uptake of the LDL by the target macrophages. It may possibly be of interest that ascorbate has been shown to react with lysyl residues under autoxidising conditions [38].…”

The presence of a glucose‐derived Maillard reaction product in the human lens

“…Studies on the synthetic mechanisms for the advanced Maillard products described above have shown that they can be synthesized by a variety of sugars other than glucose, including ascorbate oxidation products [2,4,5]. In fact, previous studies have implicated ascorbate oxidation products as the major precursors for LM-1 and pentosidine in the lens [1,2,5,6].…”

Multispecificity of Immunoglobulin M Antibodies Raised against Advanced Glycation End Products

“…In addition, DHA can be rearranged into additional degradation products, such as 2,3-diketogulonic acid, 3-deoxythreosone, xylosone, and threosone (6). These vitamin C-derived products can covalently modify proteins through nonenzymatic glycation to generate AGEs (7)(8)(9). It has been suggested that, because the vitamin C levels are high in a variety of tissues, DHA and its degradation products could be causally involved in the formation of AGEs in vivo.…”