F sub(420)H sub(2): Quinone oxidoreductase from Archaeoglobus fulgidus. Characterization of a membrane-bound multisubunit complex containing FAD and iron-sulfur clusters

• Published in: European journal of biochemistry Vol. 223; no. 2; pp. 503 - 511
• Main Authors: Kunow, J, Linder, D, Stetter, KO, Thauer, R K
• Format: Journal Article
• Language: English
• Published: 01.01.1994
• Subjects: Archaeoglobus fulgidus; Freshwater
• ISSN: 0014-2956

Archaeoglobus fulgidus, a hyperthermophilic sulfate-reducing archaeon, was found to contain a membrane-bound F sub(420)H sub(2): quinone oxidoreductase complex presumed to be involved in energy conservation during growth on lactate plus sulfate. After solubilization with dodecyl- beta -D-maltoside the complex was purified 32-fold with a yield of 24%. Using both gel filtration and native PAGE, an apparent molecular mass of approximately 270 kDa was determined. SDS/PAGE revealed the presence of at least seven polypeptides with apparent molecular masses 56, 45, 41, 39, 37, 33, and 32 kDa. The purified complex contained 1.6 mol FAD, 9 mol non-heme iron and 7 mol acid-labile sulfur/mol complex. It did not contain cytochromes, which were, however, present in the membrane fraction of A. fulgidus (3 nmol/mg membrane protein). The purified F sub(420)H sub(2):quinone oxidoreductase complex catalyzed the reduction of 2,3-dimethyl-1,4-naphthoquinone (apparent K sub(m) 190 mu M) with reduced coenzyme F sub(420) (apparent K sub(m) 50 mu M) exhibiting a specific activity of 500 U/mg (apparent V sub(max)) at pH 8.0 (pH optimum) and 65 degree C (temperature optimum). 2-Methyl-1,4-naphthoquinone (menadione), 2-hydroxy-1,4-naphthoquinone, 1,4-naphthoquinone, 2,3-dimethoxy-5-methyl-1,4-benzoquinone, and 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone (decyl-ubiquinone) were also reduced with F sub(420)H sub(2), albeit with lower rates. The physiological electron acceptor of the F sub(420)H sub(2):quinone oxidoreductase complex is most likely the menaquinone found in the membrane fraction of A. fulgidus.