Wang C S, Hartsuck J A, Downs D, Bass H A
Lipoprotein and Atherosclerosis Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104.
Biochim Biophys Acta. 1990 Apr 2;1043(2):143-8. doi: 10.1016/0005-2760(90)90287-8.
The sequential lipolysis of trioleoylglycerol and the triacylglycerols of very-low-density lipoprotein by bovine milk lipoprotein lipase can be described by the consecutive reactions: (formula: see text) where k'1, k'2 and k'3 are apparent first-order rate constants. The values of these rate constants dictate several conclusions concerning the reaction mechanism of this enzyme. The significant differences in the k'1, k'2 and k'3 values for trioleoylglycerol substrate imply that cleavage of the acyl-enzyme intermediate is not the rate-limiting step of the overall lipolysis reaction. This conclusion is further supported by the lack of an effect of hydroxylamine on the reaction rate. In addition, the observed isotope effect of k1 (H2O): k1(D2O) of 1.32 with trioleoylglycerol substrate suggests that the acyl-enzyme formation may contribute to the rate-limiting step of the lipoprotein-lipase-catalyzed reaction. In the presence of excess bovine serum albumin, the transfer of fatty acid product from the enzyme to albumin must be fast, since the k'1 values are not dependent on albumin concentration. When albumin is not in excess, the reaction is retarded and the study of reaction kinetics demonstrates negligible reaction after the available albumin is saturated.
（公式：见原文）其中k'1、k'2和k'3为表观一级速率常数。这些速率常数的值引出了关于该酶反应机制的几个结论。三油酰甘油底物的k'1、k'2和k'3值存在显著差异，这意味着酰基 - 酶中间体的裂解不是整体脂解反应的限速步骤。羟胺对反应速率无影响这一点进一步支持了该结论。此外，在三油酰甘油底物存在下观察到的k1（H2O）：k1（D2O）同位素效应为1.32，这表明酰基 - 酶的形成可能是脂蛋白脂肪酶催化反应限速步骤的一部分。在存在过量牛血清白蛋白的情况下，脂肪酸产物从酶向白蛋白的转移必定很快，因为k'1值不依赖于白蛋白浓度。当白蛋白不过量时，反应会受到阻碍，并且反应动力学研究表明，在可用白蛋白饱和后反应可忽略不计。
