Studies on the metabolism of unsaturated fatty acids. VI. Stereochemical studies of the reaction catalyzed by cis-2-enoyl-coenzyme A reductase of Escherichia coli.
作者:MICHINAO MIZUGAKI、TSUNEO UNUMA、TOMOKO NISHIMAKI、TAKAYUKI SHIRAISHI、AKIHIKO KAWAGUCHI、KAZUKI SAITO、SHIGENOBU OKUDA、HIROSHI YAMANAKA
DOI:10.1248/cpb.30.2155
日期:——
The stereochemical mechanism of the reduction of cis-2-octenoyl-coenzyme A (-CoA) catalyzed by cis-2-enoyl-CoA reductase from E. coli was studied. cis-2-[7, 8-2H5] Octenoyl-CoA was incubated with partially purified cis-2-enoyl-CoA reductase in the presence of 4R or 4S-[4-2H1] nicotinamide adenine dinucleotide phosphate (NADPH). The octenoyl-CoA was also incubated with the enzyme in the presence of NADPH in 2H2O. Octanoic acids synthesized were isolated and analyzed by gas chromatography-mass spectrometry (GC-MS) to examine the localization of deuterium atoms in the molecule. The octanoic acids isolated from the incubation mixtures were converted to their CoA esters, and then they were dehydrogenated by the action of acyl-CoA oxidase, which had previously been shown to catalyze the anti-elimination of the pro-2R and pro-3R hydrogens of acyl-CoA. The resulting products, trans-2-octenoyl-CoAs, were converted to methyl esters and their deuterium contents at the C-2 or C-3 position were also analyzed by GC-MS. The results suggested the following stereochemical features of the reaction catalyzed by cis-2-enoyl-CoA reductase. 1) pro-4R Hydrogen of NADPH was incorporated into the C-3 position of octenoyl-CoA. 2) Hydrogen from the medium was introduced into the C-2 position of octenoyl-CoA. 3) The reduction occurred by an anti-addition of hydrogen via a 2-Si, 3-Re attack on the cis-double bond.
研究了来自大肠杆菌的cis-2-烯酰辅酶A还原酶催化的cis-2-辛烯酰辅酶A(-CoA)的立体化学机制。将cis-2-[7,8-2H5]辛烯酰辅酶A与部分纯化的cis-2-烯酰辅酶A还原酶在4R或4S-[4-2H1]烟酰胺腺嘌呤二核苷酸磷酸(NADPH)存在下孵育。辛烯酰辅酶A也在NADPH和2H2O存在下与酶孵育。合成的辛酸通过气相色谱-质谱(GC-MS)分离和分析,以检查氘原子在分子中的定位。从孵育混合物中分离的辛酸被转化为它们的辅酶A酯,然后通过酰基辅酶A氧化酶的作用脱氢,此前已证明该酶催化酰基辅酶A的pro-2R和pro-3R氢的反消除反应。所得产物trans-2-辛烯酰辅酶A被转化为甲酯,其C-2或C-3位置的氘含量也通过GC-MS分析。结果表明,cis-2-烯酰辅酶A还原酶催化的反应具有以下立体化学特征:1) NADPH的pro-4R氢被并入辛烯酰辅酶A的C-3位置。2) 来自介质的氢被引入辛烯酰辅酶A的C-2位置。3) 还原反应通过反加氢,通过在顺双键上的2-Si,3-Re攻击发生。