Recently formylmethanofuran dehydrogenase from the archaebacterium Methanosarcina barkeri has been shown to be a novel molybdo-iron-sulfur protein. We report here that the enzyme contains one mol of a bound pterin cofactor/mol molybdenum, similar but not identical to the molybdopterin of milk xanthine oxidase. The two pterins, after oxidation with I2 at pH 2.5, showed identical fluorescence spectra and, after oxidation with permanganate at pH 13, yielded pterin 6-carboxylic acid. They differed, however, in their apparent molecular mass: the pterin of formylmethanofuran dehydrogenase was 400 Da larger than that of milk xanthine oxidase, a property also exhibited by the pterin cofactor of eubacterial molybdoenzymes.A homogeneous formylmethanofuran dehydrogenase preparation was used for these investigations. The enzyme, with a molecular mass of 220 kDa, contained 0.5 -0.8 mol molybdenum, 0.6-0.9 mol pterin, 28 2 mol non-heme iron and 28 2 mol acid-labile sulfur/mol based on a protein determination with bicinchoninic acid.The specific activity was 175 pmol . min-' . mg-' (k,,, = 640 s-') assayed with methylviologen (app. K, = 0.02 mM) as artificial electron acceptor. The apparent K, for formylmethanofuran was 0.02 mM.Formylmethanofuran dehydrogenase catalyzes the reversible oxidation of formylmethanofuran (CHO-MFR) to C 0 2 and methanofuran (MFR) (for structures see Fig. 1) [l].and Ti(II1) citrate (Eo' = -480 mV) as an artificial electron donor [3].Formylmethanofuran dehydrogenase is found in two groups of archaebacteria, in the methanogenic bacteria and in the sulfate-reducing, acetate-oxidizing Archaeoglobus species [l, 41. The enzyme participates in the energy metabolism of these organisms. It catalyzes the first step in C 0 2 reduction to methane (reaction b) [5] and the final step in C 0 2 formation from methanol (reaction c) [6,7] or from the methyl group of acetate (reaction d) [4]. The redox potential (E"') of the co2 + methanofuran/formylmethanofuran couple is -500 mV. The physiological electron acceptor/donor is not yet known. Methylviologen (E'' = -446 mV) can be used as an artificial electron acceptor [2]

No abstract

Formylmethanofuran dehydrogenase, a key enzyme of methanogenesis, was purified 100-fold from methanol grown Methanosarcina barkeri to apparent homogeneity and a specific activity of 34/zmol.min -1.rag protein-L Molybdenum was found to co-migrate with the enzyme activity. The molybdenum content of purified preparations was 3-4 nmol per mg protein equal to 0.64).8 mol molybdenum per tool enzyme of apparent molecular mass 200 kDa. Evidence is presented that also formylmethanofuran dehydrogenase from Hz/CO 2 grown Methanobacterium thermoautotrophicum (strain Marburg) is a molybdoenzyme.

Spores and prothallia of the fern Anemia phyllitidis L. Sw. contain a protein which in its physicochemical properties corresponds largely to calmodulin. It shows immunoreactivity with a calmodulin antiserum and activates bovine brain phosphodiesterase. Its content increases during the early processes of light-induced spore germination, indicating that the Ca(2+)-dependence of these processes may be mediated by this protein.