p-Nitrophenyl and cholesteryl-N-alkyl carbamates as inhibitors of cholesterol esterase.
p-Nitrophenyl and cholesteryl-N-alkyl carbamates as inhibitors of cholesterol esterase.
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DOI：
10.1016/s0021-9258(19)75920-1
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发表时间：
1987-01
期刊：
影响因子：
--
通讯作者：
L. Hosie;L. Sutton;D. Quinn
中科院分区：
文献类型：
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作者：
L. Hosie;L. Sutton;D. Quinn
对硝基苯和胆固醇-n -烷基氨基甲酸酯是猪胰腺胆固醇酯酶催化对硝基苯丁酸酯水解的良好抑制剂。对硝基苯基氨基丁基和氨基辛酯氨基甲酸酯（分别为化合物1和2）是该酶的有效活性位点定向不可逆抑制剂。随着抑制剂浓度的增加，化合物1或2对胆固醇酯酶的抑制表现出饱和动力学。化合物1或2存在时胆固醇酯酶的活性可被竞争性抑制剂苯硼酸保护。在牛磺酸胆酸/磷脂酰胆碱胶束存在的情况下，也观察到化合物1或2对胆固醇酯酶活性的一级降低。被抑制酶的稀释导致活性的逐渐恢复，其速率在亲核羟胺的存在下增加。因此，化合物1或2在水相或胶束相中抑制胆固醇酯酶催化的对硝基苯丁酸水解是通过碳戊酯-胆固醇酯酶机制发生的。胶束存在时，丁基碳淀粉酶的周转增加，这表明胶束对酶的催化活性有直接影响。然而，这种作用取决于底物的结构，因为辛基碳淀粉酶的周转在胶束存在时不受影响。化合物1和化合物2抑制胆固醇酯酶的二级速率常数的比较表明，辛基衍生物是更有效的抑制剂。胆固醇- n -烷基氨基甲酸酯不使胆固醇酯酶氨基甲酸酯化，而是作为可逆抑制剂。这是由于胆固醇氨基甲酸酯相对于对硝基苯氨基甲酸酯的稳定性。
p-Nitrophenyl and cholesteryl-N-alkyl carbamates are good inhibitors of porcine pancreatic cholesterol esterase-catalyzed hydrolysis of p-nitrophenyl butyrate. p-Nitrophenyl-N-butyl and N-octyl carbamates (compounds 1 and 2, respectively) are potent active site-directed irreversible inhibitors of this enzyme. The inhibition of cholesterol esterase by compound 1 or 2 shows saturation kinetics with increasing inhibitor concentration. The activity of cholesterol esterase in the presence of compound 1 or 2 can be protected by the competitive inhibitor, phenylboronic acid. First-order decreases in cholesterol esterase activity effected by compound 1 or 2 are also observed in the presence of taurocholate/phosphatidylcholine micelles. Dilution of the inhibited enzyme results in a gradual return of activity, the rate of which is increased in the presence of the nucleophile hydroxylamine. Hence, inhibition of cholesterol esterase-catalyzed hydrolysis of p-nitrophenyl butyrate by compound 1 or 2 in the aqueous or micellar phase occurs via a carbamyl-cholesterol esterase mechanism. The turnover of the butyl carbamylenzyme is increased in the presence of micelles, which indicates that the micelles have a direct effect on the catalytic activity of the enzyme. However, this effect is dependent on the structure of the substrate as the turnover of the octyl carbamylenzyme is unaffected in the presence of micelles. A comparison of the second-order rate constants for the inhibition of cholesterol esterase by compound 1 or 2 indicates that the octyl derivative is the more potent inhibitor. Cholesteryl-N-alkyl carbamates do not carbamylate cholesterol esterase but instead act as reversible inhibitors. This is due to the stability of cholesteryl carbamates relative to p-nitrophenyl carbamates.