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|Title:||Formylmethanofuran formation in Methanobacterium thermoautotrophicum|
|Author(s):||Bobik, Thomas Aquinas|
|Doctoral Committee Chair(s):||Wolfe, R.S.|
|Department / Program:||Microbiology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The initial step of methanogenesis from CO$\sb2$ is the formation of formyl-methanofuran (formyl-MFR) from methanofuran, CO$\sb2$ and H$\sb2$. This reaction is not measurable in vitro unless activated. The enzymology, and the activation of this reaction were studied.
It was found that the heterodisulfide of 2-mercaptoethanesulfonic acid and N-(7-mercaptoheptanoyl)threonine-O$\sp3$-phosphate (CoM-S-S-HTP) was directly involved in the activation of formyl-MFR formation. Preliminary evidence indicated that CoM-S-S-HTP activated electron transfer to formyl-MFR formation; CoM-S-S-HTP was found to activate an unknown electron carrier present in cell extracts of Methanobacterium, and the low potential reducing agent titanium-(III)$\cdot$citrate was found to bypass the CoM-S-S-HTP requirement of formyl-MFR synthesis. Additionally, CoM-S-S-HTP was shown to be a product of the methyl-reductase and the fumarate reductase reactions, and evidence indicated that each of these reactions activated formyl-MFR formation. Moreover, CoM-S-S-HTP was shown to be reduced by a heterodisulfide reductase and this reduction inactivated formyl-MFR formation.
Fractionation procedures were employed to resolve cell extract into two components each of which was required for formyl-MFR formation. One fraction (in the presence of CoM-S-S-HTP) reduced the redox dye metronidazole with electrons from H$\sb2$, and the other fraction contained formyl-MFR dehydrogenase activity. Neither ATP nor a membrane fraction was required to reconstitute formyl-MFR formation, and the non-deazaflavin reducing hydrogenase was sufficient for formyl-MFR formation. It was proposed that the activation of formyl-MFR formation was used to coordinate the rate of CO$\sb2$ fixation with the rates of methanogenesis and cell carbon synthesis.
|Rights Information:||Copyright 1990 Bobik, Thomas Aquinas|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9021651|