Gan K N, Smolen A, Eckerson H W, La Du B N
Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109-0626.
Drug Metab Dispos. 1991 Jan-Feb;19(1):100-6.
Evidence is presented that human serum contains a single enzyme with both paraoxonase and arylesterase activities. Throughout the steps of purification and after obtaining over 600-fold purification of the enzyme, the arylesterase activity (measured with phenylacetate as the substrate) co-eluted and retained the same ratio of activity to paraoxonase activity as it had in the initial plasma sample. Paraoxon and DFP (diisopropylfluorophosphate) both complete with phenylacetate as substrates; the inhibition is of mixed type with paraoxon and competitive with DFP. Paraoxonase and arylesterase activities require calcium, and both are inhibited to the same degree by EDTA. Purified arylesterase/paraoxonase is a glycoprotein with a minimal molecular weight of about 43,000. It has up to three sugar chains per molecule, and carbohydrate represents about 15.8% of the total weight. The enzyme has an isoelectric point of 5.1. Its amino acid composition shows nothing unusual, except for a relatively high content of leucine. We conclude that human serum arylesterase and paraoxonase activities are catalyzed by a single enzyme, capable of hydrolyzing a broad spectrum of organophosphate substrates and a number of aromatic carboxylic acid esters. Studies on the genetically determined polymorphism responsible for two allozymic forms (A and B) of the esterase are described in the following paper.
有证据表明，人血清中含有一种具有对氧磷酶和芳基酯酶活性的单一酶。在整个纯化步骤中，以及在该酶获得超过600倍的纯化后，芳基酯酶活性（以苯乙酸为底物测定）与对氧磷酶活性共洗脱，并保持了与初始血浆样品中相同的活性比。对氧磷和二异丙基氟磷酸酯（DFP）都与苯乙酸竞争作为底物；对氧磷的抑制作用为混合型，对DFP为竞争性抑制。对氧磷酶和芳基酯酶活性都需要钙，并且两者都被EDTA抑制到相同程度。纯化的芳基酯酶/对氧磷酶是一种糖蛋白，最小分子量约为43,000。每个分子最多有三条糖链，碳水化合物约占总重量的15.8%。该酶的等电点为5.1。其氨基酸组成没有异常，只是亮氨酸含量相对较高。我们得出结论，人血清芳基酯酶和对氧磷酶活性由单一酶催化，该酶能够水解多种有机磷酸底物和一些芳香族羧酸酯。下文描述了对负责酯酶两种等位酶形式（A和B）的遗传多态性的研究。
