THE F420H2-HETERODISULFIDE OXIDOREDUCTASE SYSTEM FROM METHANOSARCINA SPECIES - 2-HYDROXYPHENAZINE MEDIATES ELECTRON-TRANSFER FROM F420H2 DEHYDROGENASE TO HETERODISULFIDE REDUCTASE

F420H2-dependent CoB-S-S-CoM reduction as catalyzed by the F-420 H-2:h eterodisulfide oxidoreductase from Methanosarcina strains was observed in a defined system containing purified F420H2 dehydrogenase from Met hanosarcina mazei Go1, 2-hydrooxyphenazine and purified heterodisulfid e reductase from Methanosarcina thermophila. The process could be divi ded into two partial reactions: (1) reducing equivalents from F420H2 w ere transferred to 2-hydroxyphenazine by the F420H2 dehydrogenase with a V-max value of 12 U/mg protein; (2) reduced 2-hydroxyphenazine acte d as electron donor for CoB-S-S-CoM reduction as catalyzed by the hete rodisulfide reductase, The specific activity was 14-16 U/mg protein at 37 degrees C and 60-70 U/mg protein at 60 degrees C. The partial reac tions could be combined in the presence of both enzymes. Under these c onditions reduced 2-hydroxyphenazine was rapidly oxidized by the heter odisulfide reductase thereby producing the electron acceptor for the F 420H2 dehydrogenase, Above a concentration of 50 mu M of 2-hydroxyphen azine, the specific activity of the latter enzyme reached the V-max va lue. When other phenazines or quinone derivatives were used as electro n carriers, the activity of F420H2-dependent CoB-S-S-CoM reduction mas much lower than the rate obtained with 2-hydroxyphenazine. Thus, this water-soluble analogue of methanophenazine best mimics the natural el ectron acceptor methanophenazine in aqueous systems. (C) 1998 Federati on of European Biochemical Societies.