Huang T L, Székács A, Uematsu T, Kuwano E, Parkinson A, Hammock B D
Department of Entomology, University of California, Davis 95616.
Pharm Res. 1993 May;10(5):639-48. doi: 10.1023/a:1018987111362.
Thirty carbonates, thiocarbonates, carbamates, and carboxylic esters of alpha-naphthol, beta-naphthol, and p-nitrophenol were synthesized and tested as substrates for liver carboxylesterases from the crude microsomal fractions of human and mouse, and purified isozymes, hydrolases A and B, from rat liver microsomes. The carbonates, thiocarbonates, and carboxylic esters of alpha-naphthol were cleaved more rapidly than the corresponding beta-naphthol isomers by the mammalian liver esterases. alpha-Naphthyl esters of acetic, propionic, and butyric acids were among the best substrates tested for these enzymes. The majority of the substrates was consistently hydrolyzed at higher rates by hydrolase B compared with hydrolase A, although the Michaelis-Menten constant (Km) values of selected substrates differed widely with these two isozymes. Malathion was a 15-fold better substrate for hydrolase B than for hydrolase A. Compared with the corresponding carboxylates, the carbonate moiety of alpha- and beta-naphthol and p-nitrophenol lowered the specific activities of the enzymes by about fivefold but improved stability under basic conditions. The optimum pH of mouse liver esterase with the acetate, methyl-carbonate, and ethylthiocarbonate of alpha-naphthol was between pH 7.0 and pH 7.6. Human and mouse liver microsomal esterase activities were about five orders of magnitude lower than the esterase activities of purified rat liver hydrolase B. A relationship between the catalytic activity of the enzymes and the lipophilicity of the naphthyl substrates indicated that (i) in the alpha- and beta-naphthyl carbonate series, an inverse relationship between enzyme activity and lipophilicity of the substrates was observed, whereas (ii) in the alpha-naphthyl carboxylate series, an increase in enzyme activity with increasing lipophilicity of the substrates up to a logP value of about 4.0 was observed, after which the enzyme activity decreased.
合成了30种α-萘酚、β-萘酚和对硝基苯酚的碳酸盐、硫代碳酸盐、氨基甲酸盐和羧酸酯，并将其作为人及小鼠粗微粒体部分的肝脏羧酸酯酶以及大鼠肝脏微粒体中纯化的同工酶水解酶A和水解酶B的底物进行测试。α-萘酚的碳酸盐、硫代碳酸盐和羧酸酯被哺乳动物肝脏酯酶裂解的速度比相应的β-萘酚异构体更快。乙酸、丙酸和丁酸的α-萘酯是测试这些酶的最佳底物之一。与水解酶A相比，大多数底物被水解酶B持续以更高的速率水解，尽管所选底物的米氏常数（Km）值在这两种同工酶之间差异很大。马拉硫磷作为水解酶B的底物比作为水解酶A的底物好15倍。与相应的羧酸盐相比，α-萘酚、β-萘酚和对硝基苯酚的碳酸酯部分使酶的比活性降低了约五倍，但提高了在碱性条件下的稳定性。小鼠肝脏酯酶对α-萘酚的乙酸酯、甲基碳酸盐和乙基硫代碳酸盐的最适pH在pH 7.0至pH 7.6之间。人和小鼠肝脏微粒体酯酶活性比纯化的大鼠肝脏水解酶B的酯酶活性低约五个数量级。酶的催化活性与萘基底物的亲脂性之间的关系表明：（i）在α-和β-萘基碳酸盐系列中，观察到底物的酶活性与亲脂性呈反比关系，而（ii）在α-萘基羧酸盐系列中，观察到随着底物亲脂性增加直至logP值约为4.0时酶活性增加，此后酶活性下降。
