Model studies support pyrrolylation of the topaquinone cofactor to explain inactivation of bovine plasma amine oxidase by 3-pyrrolines. Unusual processing of a secondary amine
Model studies support pyrrolylation of the topaquinone cofactor to explain inactivation of bovine plasma amine oxidase by 3-pyrrolines. Unusual processing of a secondary amine
复制标题
DOI：
10.1021/ja9543210
复制
发表时间：
1996-07-31
影响因子：
15
通讯作者：
Sayre, LM
中科院分区：
文献类型：
--
作者：
Lee, YH;Huang, H;Sayre, LM
自从1990年报道血浆和其他铜胺氧化酶使用的活性羰基辅因子是活性部位2，4，5-三羟基苯丙氨酸残基的醌形式(托喹酮，TPQ)以来，1人们重新对机理和定向模型研究感兴趣。2-7对于该酶，似乎存在一种类似吡哆醛的转氨化机制(方案1，路径A)，因为厌氧单周转导致醛产物的释放，而NH3只有在还原的辅因子依赖于O2的再氧化时才被释放。8相反，一个加成-消除机制(方案1，路径B)，被发现是以吡咯喹啉醌为模型的苯甲胺脱氨的竞争途径，9将预测厌氧单周转后醛和NH3的同时释放。仲胺不是酶的底物10这一事实可能是合理的，因为在这种情况下，转氨反应需要两个亚胺中间体之间的互变异构化(见方案2)。然而，我们在这里传达了模型研究结果，该模型研究结果证明了仲胺发生转氨化作用，这导致我们以基于机理的失活事件的形式检测酶处理。我们最近报道了一个基于新戊酰胺乙基的模型1a，它在缓冲的乙腈水溶液中催化苯甲胺的好氧脱氨反应，4而Mure和Klinman研究了不同的托喹酮模型在无水乙腈中催化好氧脱氨反应的能力。这些最初的模型研究揭示了几个与酶有关的特征，但对催化周转的观察并非如此。
Since the report in 1990 that the active carbonyl cofactor used by plasma and other copper amine oxidases is the quinone form (topaquinone, TPQ) of an active site 2, 4, 5-trihydroxyphenylalanine residue, 1 there has been renewed interest in mechanistic and directed model studies. 2-7 A pyridoxal-like transamination mechanism appears to be in force for the enzyme (Scheme 1, path A), since anaerobic single turnover results in release of aldehyde product, whereas NH3 is released only upon O2-dependent reoxidation of the reduced cofactor. 8 In contrast, an addition-elimination mechanism (Scheme 1, path B), found to be a competing pathway for benzylamine deamination using pyrroloquinoline quinone as a model, 9 would predict simultaneous release of aldehyde and NH3 after anaerobic single turnover. The fact that secondary amines are not substrates for the enzyme10 might be rationalized on the basis that transamination in this case would require tautomerization between two iminium intermediates (see Scheme 2). However, we here communicate model study results demonstrating the occurrence of transamination for a secondary amine that led us to detect enzymatic processing in the form of a mechanism-based inactivation event.We recently reported a pivalamidoethyl-based model 1a which is active in the catalytic aerobic deamination of benzylamine in buffered aqueous acetonitrile, 4 whereas Mure and Klinman investigated the ability of various topaquinone models to catalyze aerobic deamination in anhydrous acetonitrile. 5 These initial model studies revealed several features of relevance to the enzymes, but the observation of catalytic turnover did not