Chau L Y, Tai H H
Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Kentucky, Lexington 405367-0082.
Biochim Biophys Acta. 1988 Dec 16;963(3):436-44. doi: 10.1016/0005-2760(88)90312-8.
In the present study, we have characterized the properties of both diglyceride lipase (lipoprotein lipase, EC 3.1.1.24) and monoglyceride lipases (acylglycerol lipase, EC 3.1.1.23) in an attempt to assess the potential roles of these two enzymes in the release of arachidonate in activated human platelets. Diglyceride lipase exhibited maximal activity at pH 3.5, whereas monoglyceride lipase showed optimal activity at pH 7.0. Neither of the lipases were inhibited by EDTA or stimulated by Ca2+, Mg2+ or Mn2+. Both enzymes, however, were strongly inhibited by Hg2+ and Cu2+, indicating the involvement of sulfhydryl groups in catalytic activity. This suggestion was further supported by their sensitivity toward sulfhydryl inhibitors, with monoglyceride lipase being more susceptible to inhibition. Both lipases were found to be inhibited to a different degree by a variety of antiplatelet drugs blocking aggregation and arachidonate release. Kinetic studies indicated that dichotomous metabolism of diacylglycerol to monoacylglycerol and to phosphatidic acid could occur concurrently, since the apparent Km values for diglyceride lipase and for diglyceride kinase were comparable. Further studies showed that the specific activity of monoglyceride lipase was at least 100-fold higher than that of diglyceride lipase, indicating that the rate-limiting step in the release of arachidonate was the reaction catalyzed by diglyceride lipase.
在本研究中，我们已对甘油二酯脂肪酶（脂蛋白脂肪酶，EC 3.1.1.24）和甘油单酯脂肪酶（酰基甘油脂肪酶，EC 3.1.1.23）的特性进行了表征，以评估这两种酶在活化的人血小板中花生四烯酸释放过程中的潜在作用。甘油二酯脂肪酶在pH 3.5时表现出最大活性，而甘油单酯脂肪酶在pH 7.0时表现出最佳活性。这两种脂肪酶均不受EDTA抑制，也不受Ca2+、Mg2+或Mn2+刺激。然而，这两种酶均受到Hg2+和Cu2+的强烈抑制，表明巯基参与了催化活性。它们对巯基抑制剂的敏感性进一步支持了这一观点，其中甘油单酯脂肪酶更容易受到抑制。发现这两种脂肪酶均受到多种阻断聚集和花生四烯酸释放的抗血小板药物不同程度的抑制。动力学研究表明，甘油二酯向单酰基甘油和磷脂酸的二分代谢可能同时发生，因为甘油二酯脂肪酶和甘油二酯激酶的表观Km值相当。进一步的研究表明，甘油单酯脂肪酶的比活性比甘油二酯脂肪酶至少高100倍，这表明花生四烯酸释放的限速步骤是由甘油二酯脂肪酶催化的反应。
