Olowe Y, Schulz H
J Biol Chem. 1982 May 25;257(10):5408-13.
4-Bromocrotonic acid was found to effectively inhibit respiration supported by either palmitoylcarnitine or acetoacetate in coupled rat heart mitochondria. Partial inhibition was observed when 3-hydroxybutyrate served as a substrate, whereas pyruvate-supported respiration was unaffected by the inhibitor. Thus, 4-bromocrotonic acid inhibits fatty acid oxidation and ketone body degradation. When the enzymes of beta-oxidation and ketone body degradation were assayed in mitochondria preincubated with 4-bromocrotonic acid, only 3-ketoacyl-CoA thiolase and acetoacetyl-CoA thiolase were found to be inactive. Evidence is presented for the enzymatic conversion of 4-bromocrotonic acid to 3-keto-4-bromobutyryl-CoA which effectively inhibits both thiolases. A kinetic evaluation of the inhibitions caused by 4-bromocrotonic acid in coupled rat heart mitochondria demonstrated that 3-ketoacyl-CoA thiolase and respiration supported by palmitoyl carnitine are inactivated at equal rates. However, acetoacetyl-CoA thiolase was inactivated more rapidly than was respiration supported by acetoacetate. It is suggested that the thiolase-catalyzed step is rate-limiting in beta-oxidation or is as slow as other reactions are. In contrast the thiolytic cleavage of acetoacetyl-CoA does not seem to be rate-limiting in ketone body degradation.
研究发现，4-溴巴豆酸能有效抑制大鼠离体心脏线粒体中由棕榈酰肉碱或乙酰乙酸支持的呼吸作用。当以3-羟基丁酸作为底物时，观察到部分抑制作用，而丙酮酸支持的呼吸作用不受该抑制剂影响。因此，4-溴巴豆酸可抑制脂肪酸氧化和酮体降解。在用4-溴巴豆酸预孵育的线粒体中检测β-氧化和酮体降解的酶时，发现只有3-酮酰基辅酶A硫解酶和乙酰乙酰辅酶A硫解酶无活性。有证据表明，4-溴巴豆酸可酶促转化为3-酮-4-溴丁酰辅酶A，后者可有效抑制这两种硫解酶。对4-溴巴豆酸在大鼠离体心脏线粒体中引起的抑制作用进行动力学评估表明，3-酮酰基辅酶A硫解酶和由棕榈酰肉碱支持的呼吸作用以相同速率失活。然而，乙酰乙酰辅酶A硫解酶的失活速度比由乙酰乙酸支持的呼吸作用更快。这表明硫解酶催化的步骤在β-氧化中是限速步骤，或者与其他反应一样缓慢。相比之下，乙酰乙酰辅酶A的硫解裂解在酮体降解中似乎不是限速步骤。
