Iwasaki T, Wakagi T, Oshima T
Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
J Biol Chem. 1995 Jul 28;270(30):17878-83. doi: 10.1074/jbc.270.30.17878.
To elucidate the ferredoxin-dependent redox system of the thermoacidophilic, aerobic archaeon Sulfolobus sp. strain 7, a novel FeS flavoprotein, which can reoxidize the reduced 7Fe ferredoxin in vitro, has been purified and characterized (designated as IFP) using the cognate 7Fe ferredoxin and 2-oxoacid:ferredoxin oxidoreductase, a key enzyme of the archaeal tricarboxylic acid cycle. IFP consists of three non-identical subunits with apparent molecular masses of 87, 32, and 22 kDa, respectively, and contains at least two FMN (Em, 6.8 = -57 mV) and two plant-ferredoxin-type [2Fe-2S]2+,1+ clusters (Em, 6.8 = -260 mV)/alpha 2 beta 2 gamma 2 structure. Both FeS and flavin centers of IFP are slowly but fully reduced by the enzymatically reduced cognate ferredoxin under anaerobic conditions at 50 degrees C, but not by NAD(P)H. Thus, the ferredoxin-dependent redox system of Sulfolobus sp. strain 7 is tentatively proposed as follows: 2-oxoacid:ferredoxin oxidoreductase (thiamine pyrophosphate and [4Fe-4S] cluster)-->ferredoxin-->IFP ([2Fe-2S] cluster-->FMN).
为阐明嗜热嗜酸需氧古菌硫磺硫化叶菌菌株7的铁氧化还原蛋白依赖性氧化还原系统，已使用同源7Fe铁氧化还原蛋白和2-氧代酸：铁氧化还原蛋白氧化还原酶（古菌三羧酸循环的关键酶）纯化并鉴定了一种新型FeS黄素蛋白（命名为IFP），该蛋白可在体外使还原型7Fe铁氧化还原蛋白再氧化。IFP由三个不同的亚基组成，表观分子量分别为87、32和22 kDa，包含至少两个FMN（Em, 6.8 = -57 mV）和两个植物铁氧化还原蛋白型[2Fe-2S]2+,1+簇（Em, 6.8 = -260 mV）/α2β2γ2结构。在50℃厌氧条件下，IFP的FeS和黄素中心均可被酶促还原的同源铁氧化还原蛋白缓慢但完全还原，但不能被NAD(P)H还原。因此，暂定硫磺硫化叶菌菌株7的铁氧化还原蛋白依赖性氧化还原系统如下：2-氧代酸：铁氧化还原蛋白氧化还原酶（硫胺焦磷酸和[4Fe-4S]簇）→铁氧化还原蛋白→IFP（[2Fe-2S]簇→FMN）。
