Regulation of fatty acid 18O exchange catalyzed by pancreatic carboxylester lipase. 1. Mechanism and kinetic properties.
Regulation of fatty acid 18O exchange catalyzed by pancreatic carboxylester lipase. 1. Mechanism and kinetic properties.
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胰腺羧酸酯脂肪酶催化的脂肪酸 18O 交换的调节。
DOI：
10.1021/bi00116a021
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发表时间：
1992
期刊：
影响因子：
2.9
通讯作者：
Brockman,HL
中科院分区：
文献类型：
--
作者：
Muderhwa,JM;Schmid,PC;Brockman,HL
Jean M. Muderhwa，Patricia C. Schmid和霍华德L. Brockman** The Hormel Institute，University of Minnesota，Austin，Minnesota 55912 Received April 1，1991; Revised Mandarin pt Received July 15，1991摘要：H2O和长链游离脂肪酸之间的180交换由胰羧酸酯脂肪酶（EC 1.1. 1.13）。对于水悬浮液中的棕榈酸、油酸和花生四烯酸以及单分子膜中的13，16-cz，cz-二十二碳二烯酸（DA），羧基氧与本体水相中的水氧完全交换。在氩-缓冲液界面上，无论是底物浓度还是催化浓度，DA氧的交换都遵循随机顺序机制，即180，180-DA → 180，160-DA → 160，160-DA，这表明酶-DA复合物的解离比整个交换反应中的限速步骤快得多。动力学分析，80交换表明一级依赖于表面酶和DA浓度，即，反应是有限的酰化速率。交换反应的k^ t/Km值，0.118 cm 2 pmoT1s_1，与油酸甲酯水解的值相当，并且比单层中油酸胆固醇酯水解的值高5倍[Bhat，S.，和Brockman，HL（1982）Biochemistry 21，1547]。因此，脂肪酸是羧酸酯脂肪酶的良好“底物”。与底物水平的羧酸酯脂肪酶在界面相，酰化速率常数k^ fKm是200倍，低于所获得的催化水平的酶。这表明在蛋白质覆盖的基底单层中，基底扩散可能受到限制。肠羧酸酯脂肪酶（CEL，1 EC 1.1. 1.13）在肠腔中催化简单甘油酯、溶血磷脂和维生素酯的水解（Rudd & Brockman，1984）。在肝脏中发现了相关的酶（Camulli等人，1989）和人类和其他哺乳动物的乳汁（Hui & Kissel，1990）。在消化过程中，胰羧酸酯脂肪酶在通过舌脂肪酶和胰辅脂酶依赖性脂肪酶部分消化膳食脂肪后起作用（Lindstrom等人，1988; Bernback等人，1990年），
Jean M. Muderhwa, Patricia C. Schmid, and Howard L. Brockman** The Hormel Institute, University of Minnesota, Austin, Minnesota 55912 Received April 1, 1991; Revised Manuscript Received July 15, 1991 abstract: The exchange of 180 between H20 and long-chain free fatty acids is catalyzed by pancreatic carboxylester lipase (EC 1.1. 1.13). For palmitic, oleic, and arachidonic acid in aqueous suspension and for 13, 1 6-czs, cz s-docosadienoic acid (DA) in monomolecular films, carboxyl oxygens were completely ex-changed with water oxygens of the bulk aqueous phase. With enzyme at either substrate or catalytic concentrations in the argon-buffer interface, the exchange of DA oxygens obeyed a random sequential mechanism, ie, 180,180-DA^ 180,160-DA—160,160-DA. This indicates that the dissociation of the enzyme-DA complex is much faster than the rate-limiting step in the overall exchange reaction. Kinetic analysis of, 80 exchange showed a first-order dependence on surface enzyme and DA concentrations, ie, the reaction was limited by the acylation rate. The values of k^ t/Km, 0.118 cm2 pmoT1 s" 1, for the exchange reaction was comparable to that for methyl oleate hydrolysis and 5-fold higher thanthat for cholesteryl oleate hydrolysis in monolayers [Bhat, S., & Brockman, HL (1982) Biochemistry 21, 1547]. Thus, fatty acids are good “substrates” for carboxylester lipase. With substrate levels of carboxylester lipase in the interfacial phase, the acylation rate constant k^ fKm was 200-fold lower than that obtained with catalytic levels of enzyme. This suggests a possible restriction of substrate diffusion in the protein-covered substrate monolayer.^ rincreatic carboxylester lipase (CEL, 1 EC 1.1. 1.13) cata-lyzes the hydrolysis of simple glycerides, lysophospholipids, and vitamin esters in the intestinal lumen (Rudd & Brockman, 1984). Related enzymes are found in the liver (Camulli et al., 1989) and milk of humans and other mammals (Hui & Kissel, 1990). In the digestive process, pancreatic carboxylester lipase functions after the partial digestion of dietary fats by lingual lipase and pancreatic colipase-dependent lipase (Lindstrom et al., 1988; Bernback et al., 1990) to effect the
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DOI：
10.1016/0005-2760(87)90066-x
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DOI：
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