镁离子和锰离子在红螺菌固氮酶铁蛋白的酶促激活中的作用。
The role of Mg2+ and Mn2+ in the enzyme-catalysed activation of nitrogenase Fe protein from Rhodospirillum rubrum.
作者信息
Guth J H, Burris R H
出版信息
Biochem J. 1983 Sep 1;213(3):741-9. doi: 10.1042/bj2130741.
The activation of the Fe protein of nitrogenase (Rr2) from glutamate-grown Rhodospirillum rubrum by activating enzyme (AE) was investigated. AE is confirmed to have Mr about 20 000 and is shown to operate catalytically. There is a role in activation for metal-ion-ATP, which can be met by either MnATP or MgATP. There is also a site of action for free metal ions. This site prefers Mn2+ (apparent Kd approx. 20 microM) over Mg2+ (apparent Kd approx. 20 mM) by a factor of 1000-fold. Non-activated Rr2 does not contain this binding site. MnATP is an inhibitor of C2H2 reduction, and excess Mg2+ inhibits both AE activity and C2H2 reduction, when each is studied independently under otherwise optimal conditions. The activity of AE is increased in normal reaction mixtures (in which AE activity and nitrogenase activity occur simultaneously) by Mg2+ concentrations in excess of ATP concentrations; this occurs because the excess Mg2+ prevents ATP from chelating the free Mn2+ necessary for optimal AE activity.
对来自谷氨酸培养的深红红螺菌的固氮酶铁蛋白（Rr2）被激活酶（AE）激活的过程进行了研究。已证实AE的分子量约为20000，且具有催化活性。金属离子 - ATP在激活过程中发挥作用，MnATP或MgATP均可满足这一需求。此外，还存在游离金属离子的作用位点。该位点对Mn2 +（表观解离常数Kd约为20 μM）的偏好程度比对Mg2 +（表观解离常数Kd约为20 mM）高1000倍。未激活的Rr2不含有此结合位点。在其他条件均为最佳的情况下，单独研究时，MnATP是乙炔还原的抑制剂，过量的Mg2 +会同时抑制AE活性和乙炔还原。在正常反应混合物中（AE活性和固氮酶活性同时存在），当Mg2 +浓度超过ATP浓度时，AE的活性会增加；出现这种情况的原因是过量的Mg2 +可防止ATP螯合最佳AE活性所需的游离Mn2 +。
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