New Physiological Significance of Lipase

采用PSLC色谱系统对多种脂肪酶（胰脂肪酶、羧甲酯脂肪酶、荧光假单胞菌脂肪酶和脂蛋白脂肪酶）进行了大规模纯化。用这些纯化的脂肪酶在水溶液中合成/水解酯。用阿拉伯胶乳化的油酸和十六醇与这些脂肪酶在中性pH下孵育，合成酯，并呈剂量和时间依赖性，棕榈酸酯/油酸的表观平衡比约为0.9/0.1。该脂肪酶催化阿拉伯胶乳化的油酸棕榈酯水解，油酸棕榈酯/游离油酸表观平衡比约为0.9/0.1。平衡比受孵育pH值和醇链长度的影响。当孵育pH低于7.0时，平衡比有利于酯的形成。在碱性条件下（pH 8.0以上），平衡比急剧下降。当使用酰基链短于十二醇的脂肪醇时，该比值也降低。当三油基甘油/十六醇乳液与这些脂肪酶孵育时，以剂量和时间依赖的方式合成油酸棕榈酰。脂肪酶还可由脂肪酸和视黄醇合成视黄醇酯，由脂肪酸和单酰基甘油合成二酰基甘油。这些结果表明脂肪酶通过酰基酶中间体催化酯的形成。酰基酶通过各种醇（如简单脂肪醇、视黄醇、单酰基甘油和水）的亲核攻击而去酰基化。因此，我们可以将这种脂肪酶命名为“酰基转移酶”。这些发现可用于理解脂肪酶在不同位点形成一些水不溶性酯的机理。

Various lipases (pancreatic lipase, caroxylester lipase, Pseudomonas fluorescens lipase and lipoprotein lipase) were purified on a large scale using thc PSLC chromatography system. The synthesis/hydrolysis of esters was studied in an aqueous solution using these purified lipases. When oleic acid and hexadecanol emulsified with gum araubic were incubated with these lipases at neutral pH, ester Was synthesized, in dose- and time-dependent manner, and the apparent equilibrium ratio of palmityl olcate/oleic acid was about 0.9/0.1. These lipase catalyzed the hydrolysis of palmityl oleate emulsified with gum arabic, and the apparent equilibrium ratio of palmityl oleate/free oleic acid also about 0.9/0.1. The equilibrium ratio was affected by the incubation pH and the alcohol chain length. When incubation pH was below pH 7.0 , the equilibrium ratio favored ester formation. The equilibrium ratio decreased sharply at alkaline pH (above pH 8.0). The ratio also deceased when fatty alcohols with acyl chains shorter than dodecanol were used. When trioleoylglycerol/hexadecanol emulsion was incubated with these lipases, palmityl oleate was synthesized in a dose- and time-dependent fashion. The lipase also synthesized retinyl ester from fatty acid and retinol, and diacylgycerol from fatty acid and monoacylglycerol. These results suggest that lipase catalyzes ester formation through an acyl-enzyme intermediate. The acyl-enzyme is deacylated by nucleophilic attack of various alcohols such as simple aliphatic alcohols, retinol, monoacylglycerol and water. Therefore, we might name the lipase "acyltransferase". These finding can be applied to understanding the mechanism of some water insoluble ester formations by lipase at various sites.