Autotrophic synthesis of activated acetic acid from two CO2 in Methanobacterium thermoautotrophicum |
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Authors: | Ute Holder Dumbravita-Ella Schmidt Erhard Stupperich Georg Fuchs |
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Affiliation: | (1) Abteilung Angewandte Mikrobiologie, Universität Ulm, Oberer Eselsberg, D-7900 Ulm, Germany |
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Abstract: | In a previous study with Methanobacterium thermoautotrophicum evidence was presented that methanogenesis and autotrophic synthesis of activated acetic acid from CO2 are linked processes. In this study one-carbon metabolism was investigated with growing cultures and in vitro.Serine was shown to be converted into glycine and activated formaldehyde, but only traces of label from [14C-3] of serine appeared in biosynthetic one-carbon positions. This seeming discrepancy could be explained if the same activated formaldehyde is an intermediate in biosynthesis and in methanogenesis from CO2. This hypothesis was supported by demonstrating that [14C-3] of serine and [14C] formaldehyde were rapidly converted into methane, but a small portion of the label was also specifically incorporated into the methyl group of acetate. Methane and acetate synthesis in vitro were similarly stimulated by various compounds. These experiments indicate that the methyl of acetate and methane share common one-carbon precursor(s), i.e. methylene tetrahydromethanopterin, which can also be formed enzymatically from C-3 of serine or chemically from formaldehyde.Propyl iodide 20–40 M) and methyl iodide (1–3 M) completely inhibited growth in the dark. This effect was abolished by light. Methane formation was hardly affected. When 14CH3I was applied at an only slightly inhibitory concentration, 14C was incorporated into the methyl of acetate. In vitro, similar effects on [14C] acetate formation from 14CO2 or from [14C-3] of serine were observed, except that methyl iodide did not inhibit, but even stimulated acetate synthesis. These experiments indicate that a corrinoid is involved in acetate synthesis and probably not in methanogenesis from CO2; the metal is light-reversibly alkylated and functions in methyl transfer to the acetate methyl. |
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Keywords: | Methanobacterium thermoautotrophicum Methanopterin Corrinoid Autotrophic Acetyl CoA Methane Propyl iodide Methyl iodide Serine Vitamin B12 Archaebacteria CO2 fixation |
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