光谱技术研究固氮酶铁硫簇的理化特性

Ｎ－甲基甲酰胺碱度是提取高质量固氮酶铁钼辅基的关键因素之一。过量的亚甲蓝能氧化并分解铁铜铺基为含双相铁硫簇和铁硫簇固氮酶铁钼辅基和在紫外可见光谱区中均无特征吸收峰，而在３２０ｎｍ处却呈弱吸收峰，棕色固氮菌固氮酶和该菌的突变菌侏ＵＷ４５固氮酶（缺铁钼辅基）中的非含钼的铁硫簇在紫外可见光谱区３２０ｎｍ和４０５ｎｍ处均含有特征吸收峰．

Studies on Physical-Chemical Characterization of Fe-S Clusters from Nitrogenase by Spectral Technique

Basicity of N-methylformamide(NMF) is one of key factors for extracting FeMo cofactor(FeMoco) with high quality from Azotobacter vinelandii nitrogenase.FeMoco shows enough capacity to supply electrons to reduce methyl viologen of oxidization state into one of the reducing state.Following methylene bule treatment of oxidization,FeMoco was oxidized and decomposed into Fe-S cluster containing double Mo(Mo,Fe2 )-and Fe-S cluster(Fe2 FeS6).With the addition of ferrious chelator dipyridine and thoroughly mixing to remove unstable Fe2 ,FeMoco was decomposed into Fe-S cluster containing double Mo(Mo2Fe2 FeS6)-and other simple component of Fe3 and S2-.As indicated above only FeMoco and Fe-S clusters containing double Mo were known to exhibit resemble spectral properties.They all showed a visible absorption spectrum which was featureless with gradually decreased absorbance in the 300-600 nm.Another FeS cluster of FeMoco decomposition was only known to exhibit a weak absorption peak at 320 nm.Being extracted from MoFe protein of mutant strain UW45 in the absence of FeMoco and from iron protein of Azotobarter vinelandii respectively,both Fe-S clusters clearly appeared to have resemble spectrum of characteristic absorbance at 320 nm and 405 nm.These puzzling observation let an important conclusion of both Fe-S clusters involving in similar Fe-S strucutres from the P cluster of MoFe protein in absence of FeMoco and from Fe-S cluster of iron protein respectively,and in somewhat distinguishable Fe-S cluster of FeMoco decomposition.