Dobbin P S, Butt J N, Powell A K, Reid G A, Richardson D J
School of Biological Sciences, Centre for Metalloprotein Spectroscopy and Biology, University of East Anglia, Norwich NR4 7TJ, U.K.
Biochem J. 1999 Sep 1;342 ( Pt 2)(Pt 2):439-48.
A 63.9 kDa periplasmic tetrahaem flavocytochrome c(3), designated Ifc(3), was found to be expressed in Shewanella frigidimarina NCIMB400 grown anaerobically with ferric citrate or ferric pyrophosphate as the sole terminal electron acceptor, but not in anaerobic cultures of the bacterium with other respiratory substrates. Ifc(3) was purified to homogeneity and revealed by biochemical, spectroscopic and primary structure analyses to contain four low-spin bis-His-ligated c(3)-haems, with midpoint reduction potentials of -73, -141, -174 and -259 mV. A low-potential flavin was present in the form of non-covalently bound FAD; the protein possessed a unidirectional fumarate reductase activity. Disruption of the chromosomal gene encoding Ifc(3), ifcA, did not lead to a significant change in the rate of Fe(3+) reduction in batch culture. However, during such growth the Ifc(3)-deficient mutant produced both a 35 kDa periplasmic c-type cytochrome and a 45 kDa membrane-associated c-type cytochrome at markedly higher levels than did the parent strain. Nucleotide sequencing data from directly upstream of ifcA indicated the presence of an open reading frame encoding a putative outer-membrane beta-barrel protein of 324 amino acid residues.
一种63.9 kDa的周质四血红素黄素细胞色素c(3)，命名为Ifc(3)，发现在以柠檬酸铁或焦磷酸铁作为唯一末端电子受体进行厌氧培养的嗜冷栖热袍菌NCIMB400中表达，但在该细菌以其他呼吸底物进行的厌氧培养物中不表达。Ifc(3)被纯化至同质，并通过生化、光谱和一级结构分析表明其含有四个低自旋双组氨酸连接的c(3)-血红素，中点还原电位分别为-73、-141、-174和-259 mV。一种低电位黄素以非共价结合的FAD形式存在；该蛋白质具有单向延胡索酸还原酶活性。编码Ifc(3)的染色体基因ifcA的破坏，在分批培养中并未导致Fe(3+)还原速率发生显著变化。然而，在这种生长过程中，缺乏Ifc(3)的突变体产生的35 kDa周质c型细胞色素和45 kDa膜相关c型细胞色素的水平均明显高于亲本菌株。来自ifcA直接上游的核苷酸测序数据表明存在一个开放阅读框，编码一个推定的324个氨基酸残基的外膜β-桶蛋白。
