Sulfite:Cytochrome <i>c</i> oxidoreductase from <i>Thiobacillus novellus</i> -: Purification, characterization, and molecular biology of a heterodimeric member of the sulfite oxidase family

作     者：Kappler, U Bennett, B Rethmeier, J Schwarz, G Deutzmann, R McEwan, AG Dahl, C 

作者机构：Univ Bonn Inst Mikrobiol & Biotechnol D-53115 Bonn Germany CCLRC Daresbury Lab Warrington WA4 4AD Cheshire England Univ Bremen UFT D-28334 Bremen Germany Univ Bremen Fachbereich 2 D-28334 Bremen Germany Tech Univ Carolo Wilhelmina Braunschweig Biozentrum D-38106 Braunschweig Germany Univ Regensburg Inst Biochem D-93053 Regensburg Germany Univ Queensland Dept Microbiol & Parasitol St Lucia Qld 4072 Australia 

出 版 物：《JOURNAL OF BIOLOGICAL CHEMISTRY》 (生物化学杂志)

年 卷 期：2000年第275卷第18期

页      面：13202-13212页

核心收录：

学科分类：0710[理学-生物学] 071010[理学-生物化学与分子生物学] 07[理学] 

主　　题：氨基酸序列 细菌蛋白质类/化学 细菌蛋白质类/遗传学 细菌蛋白质类/分离和提纯 细菌蛋白质类/代谢 碱基序列 细胞色素还原酶/化学 细胞色素还原酶/遗传学 细胞色素还原酶/分离和提纯 细胞色素还原酶/代谢 分子序列数据 序列比对 底物特异性 亚硫酸脱氢酶 硫杆菌属/酶学 

摘      要：Direct oxidation of sulfite to sulfate occurs in various photo- and chemotrophic sulfur oxidizing microorganisms as the final step in the oxidation of reduced sulfur compounds and is catalyzed by sulfite:cytochrome c oxidoreductase (EC 1.8.2.1), Here we show that the enzyme from Thiobacillus novellus is a periplasmically located alpha beta heterodimer, consisting of a 40.6-kDa subunit containing a molybdenum cofactor and an 8.8-kDa monoheme cytochrome c(552) smbunit (midpoint redox potential, Em(8.0) = +280 mV), The organic component of the molybdenum cofactor was identified as molybdopterin contained in a 1:1 ratio to the Mo content of the enzyme. Electron paramagnetic resonance spectroscopy revealed the presence of a sulfite-inducible Mo(V) signal characteristic of sulfite:acceptor oxidoreductases. However, pH-dependent changes in the electron paramagnetic resonance signal were not detected. Kinetic studies showed that the enzyme exhibits a ping-pong mechanism involving two reactive sites. K-m values for sulfite and cytochrome c(550) were determined to be 27 and 4 mu M, respectively;the enzyme was found to be reversibly inhibited by sulfate and various buffer ions. The sorAB genes, which encode the enzyme, appear to form an operon, which is preceded by a putative extracytoplasmic function-type promoter and contains a hairpin loop termination structure downstream of sorB. While SorA exhibits significant similarities to known sequences of eukaryotic and bacterial sulfite:acceptor oxidoreductases, SorB does not appear to be closely related to any known c-type cytochromes.