Brichac Jiri, Ho Kwok Ki, Honzatko Ales, Wang Rongying, Lu Xiaoning, Weiner Henry, Picklo Matthew J
Department of Pharmacology, Physiology, and Therapeutics, University of North Dakota, Grand Forks, North Dakota 58202-9024, USA.
Chem Res Toxicol. 2007 Jun;20(6):887-95. doi: 10.1021/tx7000509. Epub 2007 May 5.
trans-4-Hydroxy-2-nonenal (HNE) is a cytotoxic alpha,beta-unsaturated aldehyde implicated in the pathology of multiple diseases involving oxidative damage. Oxidation of HNE by aldehyde dehydrogenases (ALDHs) to trans-4-hydroxy-2-nonenoic acid (HNEA) is a major route of metabolism in many organisms. HNE exists as two enantiomers, (R)-HNE and (S)-HNE, and in intact rat brain mitochondria, (R)-HNE is enantioselectively oxidized to HNEA. In this work, we further elucidated the basis of the enantioselective oxidation of HNE by brain mitochondria. Our results showed that (R)-HNE is oxidized enantioselectively by brain mitochondrial lysates with retention of stereoconfiguration of the C4 hydroxyl group. Purified rat ALDH5A enantioselectively oxidized (R)-HNE, whereas rat ALDH2 was not enantioselective. Kinetic data using (R)-HNE, (S)-HNE, and trans-2-nonenal in combination with computer-based modeling of ALDH5A suggest that the selectivity of (R)-HNE oxidation by ALDH5A is the result of the carbonyl carbon of (R)-HNE forming a more favorable Bürgi-Duntiz angle with the active site cysteine 293. The presence of Mg2+ ions altered the enantioselectivity of ALDH5A and ALDH2. Mg2+ ions suppressed (R)-HNE oxidation by ALDH5A to a greater extent than that of (S)-HNE. However, Mg2+ ions stimulated the enantioselective oxidation of (R)-HNE by ALDH2 while suppressing (S)-HNE oxidation. These results demonstrate that enantioselective utilization of substrates, including HNE, by ALDHs is dependent upon the ALDH isozyme and the presence of Mg 2+ ions.
反式-4-羟基-2-壬烯醛（HNE）是一种具有细胞毒性的α,β-不饱和醛，与多种涉及氧化损伤的疾病病理学有关。醛脱氢酶（ALDHs）将HNE氧化为反式-4-羟基-2-壬烯酸（HNEA）是许多生物体中的主要代谢途径。HNE以两种对映体形式存在，即（R）-HNE和（S）-HNE，在完整的大鼠脑线粒体中，（R）-HNE被对映选择性地氧化为HNEA。在这项研究中，我们进一步阐明了脑线粒体对HNE进行对映选择性氧化的基础。我们的结果表明，（R）-HNE被脑线粒体裂解物对映选择性地氧化，同时保留了C4羟基的立体构型。纯化的大鼠ALDH5A对映选择性地氧化（R）-HNE，而大鼠ALDH2没有对映选择性。使用（R）-HNE、（S）-HNE和反式-2-壬烯醛的动力学数据以及基于计算机的ALDH5A建模表明，ALDH5A对（R）-HNE氧化的选择性是由于（R）-HNE的羰基碳与活性位点半胱氨酸293形成了更有利的 Bürgi-Duntiz 角。Mg2+离子的存在改变了ALDH5A和ALDH2的对映选择性。Mg2+离子对ALDH5A氧化（R）-HNE的抑制作用比对（S）-HNE的抑制作用更大。然而，Mg2+离子刺激了ALDH2对（R）-HNE的对映选择性氧化，同时抑制了（S）-HNE的氧化。这些结果表明，包括HNE在内的底物被ALDHs对映选择性利用取决于ALDH同工酶和Mg2+离子的存在。
