Lau S M, Powell P, Buettner H, Ghisla S, Thorpe C
Biochemistry. 1986 Jul 29;25(15):4184-9. doi: 10.1021/bi00363a003.
The flavoprotein medium-chain acyl coenzyme A (acyl-CoA) dehydrogenase from pig kidney exhibits an intrinsic hydratase activity toward crotonyl-CoA yielding L-3-hydroxybutyryl-CoA. The maximal turnover number of about 0.5 min-1 is 500-1000-fold slower than the dehydrogenation of butyryl-CoA using electron-transferring flavoprotein as terminal acceptor. trans-2-Octenoyl- and trans-2-hexadecenoyl-CoA are not hydrated significantly. Hydration is not due to contamination with the short-chain enoyl-CoA hydratase crotonase. Several lines of evidence suggest that hydration and dehydrogenation reactions probably utilize the same active site. These two activities are coordinately inhibited by 2-octynoyl-CoA and (methylenecyclopropyl)acetyl-CoA [whose targets are the protein and flavin adenine dinucleotide (FAD) moieties of the dehydrogenase, respectively]. The hydration of crotonyl-CoA is severely inhibited by octanoyl-CoA, a good substrate of the dehydrogenase. The apoenzyme is inactive as a hydratase but recovers activity on the addition of FAD. Compared with the hydratase activity of the native enzyme, the 8-fluoro-FAD enzyme exhibits a roughly 2-fold increased activity, whereas the 5-deaza-FAD dehydrogenase is only 20% as active. A mechanism for this unanticipated secondary activity of the acyl-CoA dehydrogenase is suggested.
猪肾中的黄素蛋白中链酰基辅酶A（酰基辅酶A）脱氢酶对巴豆酰辅酶A表现出内在的水化酶活性，生成L-3-羟基丁酰辅酶A。其最大周转数约为0.5 min⁻¹，比以电子传递黄素蛋白作为末端受体时丁酰辅酶A的脱氢反应慢500 - 1000倍。反式-2-辛烯酰辅酶A和反式-2-十六碳烯酰辅酶A的水化程度不显著。水化作用并非由于短链烯酰辅酶A水化酶巴豆酸酶的污染。多条证据表明，水化和脱氢反应可能利用相同的活性位点。这两种活性受到2-辛炔酰辅酶A和（亚甲基环丙基）乙酰辅酶A的协同抑制[它们的作用靶点分别是脱氢酶的蛋白质和黄素腺嘌呤二核苷酸（FAD）部分]。巴豆酰辅酶A的水化作用受到脱氢酶的良好底物辛酰辅酶A的严重抑制。脱辅基酶作为水化酶无活性，但添加FAD后恢复活性。与天然酶的水化酶活性相比，8-氟-FAD酶的活性大约增加了2倍，而5-脱氮-FAD脱氢酶的活性仅为天然酶的20%。本文提出了酰基辅酶A脱氢酶这种意外的二级活性的机制。
