Heterogeneous catalysis by phospholipase A2: formulation of a kinetic description of surface effects.
Heterogeneous catalysis by phospholipase A2: formulation of a kinetic description of surface effects.
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磷脂酶 A2 的多相催化：表面效应动力学描述的公式化。
DOI：
10.1139/o79-012
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
J. Wei
中科院分区：
文献类型：
--
作者：
D. Tinker;J. Wei
分析了响尾蛇磷脂酶A2（PLA）催化长链饱和磷脂酰胆碱（PC）水分散液水解的动力学，提出了考虑表面效应的反应机理。提出PLA与表面底物分子形成酶-底物复合物，从而经历构象变化，暴露与脂质表面相互作用的位点。在水解事件之后，酶可以从表面解吸（路径1），或者沿着表面扩散到相邻的底物分子（路径2）。路径1主导的机制导致Michaelis-Menton稳态动力学，并表征凝胶相PC的水解。在高酶浓度下获得PLA表面饱和的证据。当解吸速率非常小时，路径2机制占主导地位;该机制描述了液晶相PC的水解，其特征在于水解的初始爆发，然后是非常缓慢的反应。在这两个阶段的反应速度是独立的散装PC浓度。当凝胶和液晶PC相共存时，如在二肉豆蔻酰-PC和二硬脂酰-PC的混合物中，液晶相优先水解。反应产物（溶血PC和脂肪酸）刺激水解，显然是通过刺激解吸附的PLA。的解吸速率常数似乎是一个线性函数的表面浓度的lyso-PC和脂肪酸。所提出的模型描述了水解进展曲线非常好，是一致的，与目前的想法，这种酶的催化机制。
The kinetics of hydrolysis of aqueous dispersion of long-chain, saturated phosphatidylcholines (PC) catalysed by Crotalus atrox phospholipase A2 (PLA) have been analyzed, and a reaction mechanism proposed which takes surface effects into account. PLA is proposed to form an enzyme-substrate complex with surface substrate molecules, thereby undergoing a conformational change which exposes sites that interact with the lipid surface. After a hydrolytic event, the enzyme can either desorb from the surface (path 1), or diffuse along the surface to an adjacent substrate molecule (path 2). The path 1 dominated mechanism leads to Michaelis-Menton steady-state kinetics, and characterizes hydrolysis of gel phase PC. Evidence for saturation of the surface with PLA was obtained at high enzyme concentrations. The path 2 mechanism dominates when the desorption rate is very small; this mechanism describes hydrolysis of liquid crystalline phase PC and is characterized by an initial burst of hydrolysis followed by a very slow reaction. The velocities in these two phases of the reaction are independent of bulk PC concentration. When gel and liquid crystalline PC phases coexist, as in mixtures of dimyristoyl- and distearoyl-PC, the liquid crystalline phase is preferentially hydrolysed. Products of the reaction (lyso-PC and fatty acid) stimulated hydrolysis, apparently by stimulating desorption of PLA. The desorption rate constant appears to be a linear function of the surface concentrations of lyso-PC and fatty acid. The proposed model describes hydrolysis progress curves extremely well and is consistent with current ideas on the mechanism of catalysis by this enzyme.