Tserng K Y, Jin S J
Medical Research Service, VA Medical Center, Cleveland, Ohio.
J Biol Chem. 1991 Jun 25;266(18):11614-20.
Cis-5 double bond in a fatty acid or when encountered through the beta-oxidation of an odd-numbered double-bond unsaturated fatty acid presents as a metabolic block to the further beta-oxidation. Cis-5-fatty acyl-CoA cannot be beta-oxidized to cis-3-enoyl-CoA as suggested by the conventional pathway. Instead, this metabolic block can only be removed through an NADPH-dependent reduction of 5-enoyl-CoA, possibly mediated by a 5-enoyl-CoA reductase. In the case of oleic acid two cycles of beta-oxidation yield cis-5-tetradecenoyl-CoA. This intermediate is then reduced to tetradecanoyl-CoA, which is metabolized further via normal beta-oxidation cycles. The conventional pathway through cis-3-dodecenoyl-CoA does not operate in rat liver.
脂肪酸中的顺式-5双键，或者在奇数双键不饱和脂肪酸的β-氧化过程中遇到的顺式-5双键，会成为进一步β-氧化的代谢障碍。顺式-5-脂肪酰辅酶A不能像传统途径所表明的那样被β-氧化为顺式-3-烯酰辅酶A。相反，这种代谢障碍只能通过由烟酰胺腺嘌呤二核苷酸磷酸（NADPH）依赖的5-烯酰辅酶A还原反应来消除，这一反应可能由5-烯酰辅酶A还原酶介导。以油酸为例，两个β-氧化循环会产生顺式-5-十四碳烯酰辅酶A。然后这种中间产物被还原为十四烷酰辅酶A，它会通过正常的β-氧化循环进一步代谢。通过顺式-3-十二碳烯酰辅酶A的传统途径在大鼠肝脏中不起作用。
