Isolation and Characterization of Methanophenazine and Function of Phenazines in Membrane-Bound Electron Transport ofMethanosarcina mazeiGö1

Open Access
Publisher Website
Google Scholar
Abstract
A hydrophobic, redox-active component with a molecular mass of 538 Da was isolated from lyophilized membranes ofMethanosarcina mazeiGö1 by extraction with isooctane. After purification on a high-performance liquid chromatography column, the chemical structure was analyzed by mass spectroscopy and nuclear magnetic resonance studies. The component was called methanophenazine and represents a 2-hydroxyphenazine derivative which is connected via an ether bridge to a polyisoprenoid side chain. Since methanophenazine was almost insoluble in aqueous buffers, water-soluble phenazine derivatives were tested for their ability to interact with membrane-bound enzymes involved in electron transport and energy conservation. The purified F420H2dehydrogenase fromM. mazeiGö1 showed highest activity with 2-hydroxyphenazine and 2-bromophenazine as electron acceptors when F420H2was added. Phenazine-1-carboxylic acid and phenazine proved to be less effective. TheKmvalues for 2-hydroxyphenazine and phenazine were 35 and 250 μM, respectively. 2-Hydroxyphenazine was also reduced by molecular hydrogen catalyzed by an F420-nonreactive hydrogenase which is present in washed membrane preparations. Furthermore, the membrane-bound heterodisulfide reductase was able to use reduced 2-hydroxyphenazine as an electron donor for the reduction of CoB-S-S-CoM. Considering all these results, it is reasonable to assume that methanophenazine plays an important role in vivo in membrane-bound electron transport ofM. mazeiGö1.