Identification of N epsilon-carboxymethyllysine as a degradation product of fructoselysine in glycated protein.
Identification of N epsilon-carboxymethyllysine as a degradation product of fructoselysine in glycated protein.
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发表时间：
1986-04
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通讯作者：
M. U. Ahmed;S. Thorpe;J. Baynes
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作者：
M. U. Ahmed;S. Thorpe;J. Baynes
以蛋白质中的糖基化赖氨酸残基的类似物N α-甲酰基-N ε-果糖赖氨酸（fFL）为模型化合物，研究了糖基化蛋白质的美拉德或布朗宁反应的化学性质。在生理pH和温度下在0.2M磷酸盐缓冲液中孵育fFL（15 mM）导致在15天后以约40%的产率形成N ε-羧甲基赖氨酸（CML）。CML是通过碳水化合物链的C-2和C-3之间的fFL的氧化裂解形成的，并且阿糖膦酸（EA）被鉴定为反应中形成的裂解产物。在氮气气氛下，fFL既没有形成CML，也没有形成EA。CML的形成速率取决于孵育混合物中的磷酸盐浓度，并且该反应显示通过自由基机制发生。CML也确定了在磷酸盐缓冲液中在空气中糖化的多聚-L-赖氨酸和牛胰腺核糖核酸酶的水解产物中的氨基酸分析。通过HPLC法在人透镜蛋白和组织胶原中也检测到CML，并通过气相色谱/质谱法确认了鉴别。人尿中CML和EA的存在表明它们是通过体内糖化蛋白的降解形成的。fFL孵育混合物的布朗宁在氮气气氛下比在空气气氛下进行更大程度，表明Amadori加合物氧化降解形成CML可能限制糖化蛋白的布朗宁反应。由于反应产物CML和EA在化学和代谢上都是相对惰性的，Amadori加合物的氧化裂解可能在限制体内蛋白质糖化的后果中起作用。
The chemistry of Maillard or browning reactions of glycated proteins was studied using the model compound, N alpha-formyl-N epsilon-fructoselysine (fFL), an analog of glycated lysine residues in protein. Incubation of fFL (15 mM) at physiological pH and temperature in 0.2 M phosphate buffer resulted in formation of N epsilon-carboxymethyllysine (CML) in about 40% yield after 15 days. CML was formed by oxidative cleavage of fFL between C-2 and C-3 of the carbohydrate chain and erythronic acid (EA) was identified as the split product formed in the reaction. Neither CML nor EA was formed from fFL under a nitrogen atmosphere. The rate of formation of CML was dependent on phosphate concentration in the incubation mixture and the reaction was shown to occur by a free radical mechanism. CML was also identified by amino acid analysis in hydrolysates of both poly-L-lysine and bovine pancreatic ribonuclease glycated in phosphate buffer under air. CML was also detected in human lens proteins and tissue collagens by HPLC and the identification was confirmed by gas chromatography/mass spectroscopy. The presence of both CML and EA in human urine suggests that they are formed by degradation of glycated proteins in vivo. The browning of fFL incubation mixtures proceeded to a greater extent under a nitrogen versus an air atmosphere, suggesting that oxidative degradation of Amadori adducts to form CML may limit the browning reactions of glycated proteins. Since the reaction products, CML and EA, are relatively inert, both chemically and metabolically, oxidative cleavage of Amadori adducts may have a role in limiting the consequences of protein glycation in the body.