Sugumaran M, Schinkmann K, Dali H
Department of Biology, University of Massachusetts, Boston 02125.
Arch Insect Biochem Physiol. 1990;14(2):93-109. doi: 10.1002/arch.940140205.
The mechanism of oxidation of 1,2-dehydro-N-acetyldopamine (dehydro NADA) was examined to resolve the controversy between our group and Andersen's group regarding the reactive species involved in beta-sclerotization. While Andersen has indicated that dehydro NADA quinone is the beta-sclerotizing agent [Andersen, 1989], we have proposed quinone methides as the reactive species for this process [Sugumaran, 1987; Sugumaran, 1988]. Since dehydro NADA quinone has not been isolated or identified till to date, we studied the enzymatic oxidation of dehydro NADA in the presence of quinone traps to characterize this intermediate. Accordingly, both N-acetylcysteine and o-phenylenediamine readily trapped the transiently formed dehydro NADA quinone as quinone adducts. Interestingly, when the enzymatic oxidation was performed in the presence of o-aminophenol or different catechols, adduct formation between the dehydro NADA side chain and the additives had occurred. The structure of the adducts is in conformity with the generation and reactions of dehydro NADA quinone methide (or its radical). This, coupled with the fact that 4-hydroxyl or amino-substituted quinones instantly transformed into p-quinonoid structure, indicates that dehydro NADA quinone is only a transient intermediate and that it is the dehydro NADA quinone methide that is the thermodynamically stable product. However, since this compound is chemically more reactive due to the presence of both quinone methide and acylimine structure on it, the two side chain carbon atoms are "activated." Based on these considerations, it is suggested that the quinone methide derived from dehydro NADA is the reactive species responsible for cross-link formation between dehydro NADA and cuticular components during beta-sclerotization.
对1,2 - 脱氢 - N - 乙酰多巴胺（脱氢NADA）的氧化机制进行了研究，以解决我们小组与安徒生小组之间关于β - 硬化过程中涉及的活性物种的争议。安徒生指出脱氢NADA醌是β - 硬化剂[安徒生，1989]，而我们则提出醌甲基化物是该过程的活性物种[苏古马兰，1987；苏古马兰，1988]。由于脱氢NADA醌至今尚未被分离或鉴定出来，我们在醌捕获剂存在的情况下研究了脱氢NADA的酶促氧化，以表征这种中间体。因此，N - 乙酰半胱氨酸和邻苯二胺都很容易将瞬时形成的脱氢NADA醌捕获为醌加合物。有趣的是，当在邻氨基酚或不同儿茶酚存在下进行酶促氧化时，脱氢NADA侧链与添加剂之间发生了加合物形成。加合物的结构与脱氢NADA醌甲基化物（或其自由基）的生成和反应一致。这一点，再加上4 - 羟基或氨基取代的醌会立即转化为对醌结构这一事实，表明脱氢NADA醌只是一个瞬时中间体，而脱氢NADA醌甲基化物才是热力学稳定产物。然而，由于该化合物因其上同时存在醌甲基化物和酰亚胺结构而在化学上更具反应性，两个侧链碳原子被“激活”。基于这些考虑，有人提出，脱氢NADA衍生的醌甲基化物是在β - 硬化过程中负责脱氢NADA与表皮成分之间交联形成的活性物种。
