Roberts B J, Knights K M
Department of Clinical Pharmacology, Flinders University of South Australia, Adelaide.
Biochem Pharmacol. 1992 Jul 22;44(2):261-7. doi: 10.1016/0006-2952(92)90008-7.
ATP-dependent coenzyme A (CoA) ligases catalyse the formation of the acyl-CoA thioesters of xenobiotic carboxylic acids and the formation of xenobiotic-CoAs has been implicated as being a causative factor in peroxisomal proliferation. In this study we have demonstrated using rat liver peroxisomes that the formation of palmitoyl-CoA is inhibited by a variety of xenobiotic carboxylic acids. Palmitoyl-CoA formation exhibited biphasic kinetics indicative of two isoforms, a high affinity (Km1 2.3 microM) low capacity form and a low affinity (Km2 831 microM) high capacity form. These forms were differentially inhibited by a range of xenobiotics. However, it would appear that the low affinity component may not contribute to any major extent to the formation of xenobiotic-CoAs in vivo. At a concentration of 1 mM, greater than 20% inhibition of the high affinity form was observed with the 2-arylpropionates, ibuprofen, naproxen, benoxaprofen, fenoprofen, indoprofen, ketoprofen, tiaprofenic acid and cicloprofen, the hypolipidaemics, nafenopin and ciprofibrate, and the herbicides, silvex and 2,4,5-trichlorophenoxyacetate. Valproic acid, clofibric acid, salicylic acid and 2,4-dichlorophenoxy-acetate were non-inhibitory at all concentrations studied (0.1-2.5 mM). Analysis of the type of inhibition established that only nafenopin (Ki 430 microM) and ciprofibrate (Ki 97 microM) were competitive inhibitors of palmitoyl-CoA formation suggesting that they bind at the active site and thus potentially function as alternative substrates for the peroxisomal ligase. Notably, clofibric acid which has previously been shown to form clofibroyl-CoA in peroxisomes did not interact with the palmitoyl-CoA ligase thereby suggesting that activation is mediated via an alternative peroxisomal CoA ligase. In addition, the xenobiotic inhibitors of the peroxisomal palmitoyl-CoA ligase differed from those previously reported for the equivalent microsomal enzyme suggesting that the organellar forms may be functionally distinct. This study establishes that numerous xenobiotic carboxylic acids interact with the peroxisomal palmitoyl-CoA ligase; however, it would appear that relatively few function as alternative substrates. The toxicological ramifications of peroxisomally mediated xenobiotic-CoA formation and the identification of other peroxisomal xenobiotic-CoA ligase(s) remain to be elucidated.
ATP 依赖性辅酶 A（CoA）连接酶催化异源生物羧酸的酰基辅酶 A 硫酯的形成，而异源生物-CoA 的形成被认为是过氧化物酶体增殖的一个致病因素。在本研究中，我们使用大鼠肝脏过氧化物酶体证明了多种异源生物羧酸可抑制棕榈酰辅酶 A 的形成。棕榈酰辅酶 A 的形成表现出双相动力学，表明存在两种同工型，一种是高亲和力（Km1 为 2.3 μM）、低容量形式，另一种是低亲和力（Km2 为 831 μM）、高容量形式。这些形式受到一系列异源生物的不同程度抑制。然而，低亲和力组分在体内对异源生物-CoA 的形成可能没有太大贡献。在 1 mM 的浓度下，2-芳基丙酸类药物布洛芬、萘普生、苯恶洛芬、非诺洛芬、吲哚洛芬、酮洛芬、噻洛芬酸和环氯洛芬、降血脂药氯贝丁酯和安妥明，以及除草剂 2,4,5-涕丙酸和 2,4,5-三氯苯氧乙酸对高亲和力形式的抑制率超过 20%。丙戊酸、氯贝酸、水杨酸和 2,4-二氯苯氧乙酸在所有研究浓度（0.1 - 2.5 mM）下均无抑制作用。对抑制类型的分析表明，只有氯贝丁酯（Ki 为 430 μM）和安妥明（Ki 为 97 μM）是棕榈酰辅酶 A 形成的竞争性抑制剂，这表明它们在活性位点结合，因此可能作为过氧化物酶体连接酶的替代底物发挥作用。值得注意的是，先前已证明在过氧化物酶体中形成氯贝酰辅酶 A 的氯贝酸并未与棕榈酰辅酶 A 连接酶相互作用，从而表明激活是通过另一种过氧化物酶体辅酶 A 连接酶介导的。此外，过氧化物酶体棕榈酰辅酶 A 连接酶的异源生物抑制剂与先前报道的等效微粒体酶的抑制剂不同，这表明细胞器形式在功能上可能不同。本研究证实，许多异源生物羧酸与过氧化物酶体棕榈酰辅酶 A 连接酶相互作用；然而，似乎相对较少的异源生物羧酸作为替代底物起作用。过氧化物酶体介导的异源生物-CoA 形成的毒理学影响以及其他过氧化物酶体异源生物-CoA 连接酶的鉴定仍有待阐明。
