INTERACTION OF SUGAR PHOSPHATES WITH THE CATALYTIC SITE OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE
INTERACTION OF SUGAR PHOSPHATES WITH THE CATALYTIC SITE OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE
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DOI：
10.1021/bi00511a023
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发表时间：
1981-01-01
期刊：
影响因子：
2.9
通讯作者：
LORIMER, GH
中科院分区：
文献类型：
--
作者：
BADGER, MR;LORIMER, GH
[来自菠菜叶]的核酮糖-1，5-二磷酸羧化酶的活化和催化活性形式是酶-活化剂CO2·Mg的三元复合物。效应物NADPH和6-磷酸葡萄糖酸通过形成酶··活化剂CO 2··Mg··效应物的快速平衡四元复合物促进活化;效应物本身不活化酶，但通过稳定活化的酶··活化剂CO 2·Mg···复合物促进基本活化过程。动力学和凝胶过滤研究表明，效应器稳定的激活剂CO2和Mg 2+（或Mn 2+）的结合，从而降低失活率。结合研究表明每个原聚体存在一个6-磷酸葡萄糖酸结合位点。当核酮糖二磷酸的催化位点被过渡态类似物2-羧基阿拉伯糖醇1，5-二磷酸占据时，6-磷酸葡糖酸和NADPH与酶激活剂CO2·Mg复合物的结合被完全阻止，并且在羧化反应产物3-磷酸甘油酸存在下竞争性减少。NADPH，6-磷酸葡萄糖酸和3-磷酸甘油酸作为线性竞争抑制剂的羧化相对于核酮糖二磷酸。效应子通过在核酮糖二磷酸的催化位点处的相互作用引起它们的响应，并且它们的作用是次要的，以碱性CO2-Mg 2+依赖性活化反应。酶分子不能同时具有催化活性和被效应物激活，因为后者涉及核酮糖二磷酸结合位点的占据。
The activated and catalytically competent form of ribulose-1,5-bisphosphate carboxylase [from spinach leaves] is a ternary complex of enzyme-activator CO2.cntdot.Mg. The effectors NADPH and 6-phosphogluconate promoted activation by formation of a rapid equilibrium quaternary complex of enzyme.cntdot.activator CO2.cntdot.Mg.cntdot.effector; the effectors did not activate the enzyme per se but promoted the basic activation process by stabilizing the activated enzyme.cntdot.activator CO2.cntdot.Mg complex. Kinetic and gel filtration studies showed that the effectors stabilized the binding of the activator CO2 and Mg2+ (or Mn2+), thereby decreasing the rate of deactivation. Binding studies indicated the presence of one 6-phosphogluconate binding site per protomer. The binding of 6-phosphogluconate and NADPH to the enzyme.cntdot.activator CO2.cntdot.Mg complex was completely prevented when the catalytic site for ribulose bisphosphate was occupied by the transition-state analog, 2-carboxyarabinitol 1,5-bisphosphate and competitively diminished in the presence of 3-phosphoglycerate, the product of the carboxylation reaction. NADPH, 6-phosphogluconate and 3-phosphoglycerate acted as linear competitive inhibitors of carboxylation with respect to ribulose bisphosphate. The effectors elicit their response through interaction at the catalytic site for ribulose bisphosphate and their effect is secondary to the basic CO2-Mg2+-dependent activation reaction. An enzyme molecule cannot be simultaneously catalytically competent and activated by an effector, since the latter involves occupancy of the ribulose bisphosphate binding site.