钙离子对江浙蝮蛇毒酸性磷脂酶A_2结构与功能的影响

钙离子在江浙蝮蛇毒酸性磷脂酶Ａ_２中的作用是多方面的。它不仅能够引起酸性磷脂酶Ａ_２在溶液中构象的变化，而且对该酶活性有较大的影响。Ｃａ~（２＋）为酶活力所必需，当Ｃａ~（２＋）浓度达到０．０６ｍｍｏｌ／Ｌ时，酶表现出很高的活力；Ｃａ~（２＋）浓度超过０．５ｍｍｏｌ／Ｌ时，催化反应出现一个明显的延滞期。化学修饰表明Ｈｉｓ_（４７）在表现活力方面起重要作用，Ｃａ~（２＋）的存在可降低其修饰反应的速度，提示这是由于Ｃａ~（２＋）引起构象发生变化而造成的。

Effect of Calcium Ion on the Structure and Function of Phospholipase A_2 from the Venom of Agkistrodon Halys Pallas

Calcium ion has multiply-aspect interaction with acidic phospholipase A_2 from Agkistrodon halys Pallas. Not only does it influence the conformation of the enzyme in aqueous solvent, but also has quite a lot effect on its activity. Calcium ion is necessary for phospholipase A_2 on the hydrolysis of phospholipids, and 0. 06mM Ca￣(2+) is the optimum concentration to express the enzyme activity. However, when it reaches to 0. 5mM, a lag period of hydrolysis reaction appeared. Presence of calcium ion can diminish the modification speed of P-bromophenacyl bromide on histidine-47 which leads to the inactivation of the enzyme, this shows His-47 is a critical resdue to the molecule. The result suggests that interaction of calcium causes conformation change, thus protects His against modification.