Jakas Andreja, Horvat Stefica
Division of Organic Chemistry and Biochemistry, Rudjer Bosković Institute, P. O. B. 180, HR-10002 Zagreb, Croatia.
Biopolymers. 2003 Aug;69(4):421-31. doi: 10.1002/bip.10338.
Reactions between biological amines and reducing sugars (the Maillard reaction) are among the most important of the chemical and oxidative changes occurring in biological systems that contribute to the formation of a complex family of rearranged and dehydrated covalent adducts that have been implicated in the pathogenesis of human diseases. In this study, chemistry of the Maillard reactions was studied in four model systems containing fructosamines (Amadori compounds) obtained from the endogenous opioid pentapeptide leucine-enkephalin (Tyr-Gly-Gly-Phe-Leu), leucine-enkephalin methyl ester, structurally related tripeptide (Tyr-Gly-Gly), or from amino acid (Tyr). The degradation of model compounds as well as their ability to develop Maillard fluorescence was investigated under oxidative conditions in methanol and phosphate buffer pH 7.4 at two different temperatures (37 and 70 degrees C). At 37 degrees C, glycated leucine-enkephalin degraded slowly in methanol (t(1/2) approximately 13 days) and phosphate buffer (t(1/2) approximately 9 days), producing a parent peptide compound as a major product throughout a three-week incubation period. Whereas fluorescence slowly increased over time at 37 degrees C, incubations off all studied Amadori compounds at 70 degrees C resulted in a rapid appearance of a brown color and sharp increase in AGE (advanced glycation end products)-associated fluorescence (excitation 320 nm/emmision 420 nm) as well as in distinctly higher amounts of fragmentation products. The obtained data indicated that the shorter the peptide chain the more degradation products were formed. These studies have also helped to identify a new chemical transformation of the peptide backbone in the Maillard reaction that lead to beta-scission of N-terminal tyrosine side chain and p-hydroxybenzaldehyde formation under both aqueous and nonaqueous conditions.
生物胺与还原糖之间的反应（美拉德反应）是生物系统中发生的最重要的化学和氧化变化之一，这些变化导致形成了一系列复杂的重排和脱水共价加合物，这些加合物与人类疾病的发病机制有关。在本研究中，在四个模型系统中研究了美拉德反应的化学过程，这些系统包含从内源性阿片肽五肽亮氨酸脑啡肽（Tyr-Gly-Gly-Phe-Leu）、亮氨酸脑啡肽甲酯、结构相关的三肽（Tyr-Gly-Gly）或氨基酸（Tyr）获得的果糖胺（阿马多里化合物）。在甲醇和pH 7.4的磷酸盐缓冲液中，于两个不同温度（37和70摄氏度）的氧化条件下，研究了模型化合物的降解及其产生美拉德荧光的能力。在37摄氏度时，糖化的亮氨酸脑啡肽在甲醇中降解缓慢（半衰期约为13天），在磷酸盐缓冲液中降解也缓慢（半衰期约为9天），在为期三周的孵育期内，主要产物为母体肽化合物。虽然在37摄氏度时荧光随时间缓慢增加，但在70摄氏度下对所有研究的阿马多里化合物进行孵育时，会迅速出现棕色，与晚期糖基化终产物（AGE）相关的荧光（激发波长320nm/发射波长420nm）急剧增加，并且碎片产物的量明显更高。获得的数据表明，肽链越短，形成的降解产物越多。这些研究还有助于确定美拉德反应中肽主链的一种新的化学转化，即在水性和非水性条件下都会导致N端酪氨酸侧链的β-断裂和对羟基苯甲醛的形成。
