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N_(2)和NH~(+)_(4)培养下粪产碱菌固氮酶铁蛋白圆二色谱及热力学特性比较

海伟力, 宋未, 尤崇杓, 李忠, 王文清

中国农业科学院原子能利用研究所. 北京(100094)；北京大学技术物理系. 北京(100871)

摘要

N_(2)和NH~(+)_(4)培养下粪产碱菌固氮酶铁蛋白(分别为Af2和Af~(* )2)的氧化态和还原态的CD谱及MCD谱存在明显差异。还原态Af2与Af~(*)2在210nm附近的MCD谱完全不同, 但其氧化态MCD谱相同。热力学测定结果表明, 在298°K、1.013×10~(5)Pa下, Af2与MgATP饱合络合时的焓(△H°)变化为-27.0kJ/mol, 自由能(△G°) 变化则为-20.8kJ/mol, 熵(△S°)变化为-20.6Jmol~(-1)K~(-1)。而Af~(*)2与MgATP饱合络合时的焓变化为-44.35kJ/mol, 自由能变化为-20.4kJ/mol, 熵变化为-79.9Jmol~(-1)K~(-1)。Af2与MgATP络合后再与N_(2)培养的钼铁蛋白反应为吸热反应, 而Af~(*)2与MgATP络合后再与NH~(+)_(4)培养的钼铁蛋白反应为放热反应。图6参14

关键词： 粪产碱菌; 固氮酶; 铁蛋白; 圆二色谱; 热力学参数

The CD spectra and thermodynamic properties of the iron protein of nitrogenase from N_(2)-and NH~(+)_(4)-grown Alcaligenes faecalis

Hai Weili, Song Wei, You Chongbiao, Li Zhong, Wang Wenqing

Institute for Application of Atomic Energy, CAAS. Beijing；China(100871)

Abstract

The purified iron proteins(Af2 and Af*2)of nitrogenase from Alcaligenes faecalis strain A1501 cells grown under N_(2) and under NH_(4)~(+)(30 mmol/L) respectively were used in this study. The specific activity of Af2 was 1540 nmol C_(2)H_(4)formed mg~(-1) protein min~(-1). and no activity of Af*2 was observed. The circular dichoism(CD)and magnetic CD(MCD)were measured in both reduced and oxidized states. Af2 and Af*2 differed from each other in their CD spectra, particularly in the oxidized states. After oxidization, the 210 nm peak of the CD spectra from Af2 was shifted to the far-UV region, while the spectra of Af*2 was almost unchanged. The MCD spectra of the reduced states of Af2 and Af*2 were quite different, but these of the oxidized states were the same, suggesting that their molecular structure and the environmental conditions around the 4Fe-4S cluster might be different.

Key words: Alcaligenes faecalis;Iron protein;Nitrogenase;CD spectra;Thermodynamic parameter

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引用本文：

海伟力, 宋未, 尤崇杓, 李忠, 王文清. N_(2)和NH~(+)_(4)培养下粪产碱菌固氮酶铁蛋白圆二色谱及热力学特性比较[J]. 生理学报 1994; 46 (1): .

Hai Weili, Song Wei, You Chongbiao, Li Zhong, Wang Wenqing. The CD spectra and thermodynamic properties of the iron protein of nitrogenase from N_(2)-and NH~(+)_(4)-grown Alcaligenes faecalis. Acta Physiol Sin 1994; 46 (1): (in Chinese with English abstract).