Kasuya F, Yamaoka Y, Igarashi K, Fukui M
Faculty of Pharmaceutical Sciences, Kobe-Gakuin University, Kobe, Japan.
Biochem Pharmacol. 1998 Jun 1;55(11):1769-75. doi: 10.1016/s0006-2952(97)00640-0.
Amino acid conjugation is an important route of detoxification of xenobiotic and endogenous carboxylic acids. The specificity of the purified medium chain acyl-CoA synthetase catalyzing the first reaction of amino acid conjugation was investigated further for substrates and inhibitors. Molecular modeling techniques were applied to derive the molecular characteristics of substrates and inhibitors for the medium chain acyl-CoA synthetase. The purified enzyme accepted not only straight medium chain fatty acids but also aromatic acids. Of the arylacetic acids, activity was obtained with naphthylacetic acids, whereas introduction of a methyl group at the alpha-position caused loss of activity. High activity was also observed with cyclohexanoic acid. Diflunisal, 2-hydroxydodecanoic acid, and nalidixic acid inhibited the medium chain acyl-CoA synthetase activity for hexanoic acid, with Ki values of 0.8, 4.4, and 12.3 microM, respectively. The inhibitory carboxylic acids were competitive with respect to hexanoic acid. The hydroxyl or ketone (oxo) groups at the beta-position of carboxylic acids were an important determinant for inhibitory activity. All substrates and inhibitors contained a flat hydrophobic region coplanar to the carboxylate group. In addition, the substrates had negative values for charge on the carbon in the beta-position of carboxylic acids.
氨基酸结合是外源性和内源性羧酸解毒的重要途径。进一步研究了催化氨基酸结合第一步反应的纯化中链酰基辅酶A合成酶对底物和抑制剂的特异性。应用分子建模技术推导中链酰基辅酶A合成酶底物和抑制剂的分子特征。纯化后的酶不仅能接受直链中链脂肪酸，还能接受芳香酸。在芳基乙酸中，萘乙酸具有活性，而在α位引入甲基会导致活性丧失。环己烷酸也表现出高活性。双氯芬酸、2-羟基十二烷酸和萘啶酸抑制中链酰基辅酶A合成酶对己酸的活性，其抑制常数（Ki）分别为0.8、4.4和12.3微摩尔。抑制性羧酸与己酸具有竞争性。羧酸β位的羟基或酮（氧代）基团是抑制活性的重要决定因素。所有底物和抑制剂都含有一个与羧基共面的扁平疏水区域。此外，底物在羧酸β位的碳原子上带有负电荷。
