Formylmethanofuran formation in Methanobacterium thermoautotrophicum
Bobik, Thomas Aquinas
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https://hdl.handle.net/2142/22839
Description
Title
Formylmethanofuran formation in Methanobacterium thermoautotrophicum
Author(s)
Bobik, Thomas Aquinas
Issue Date
1990
Doctoral Committee Chair(s)
Wolfe, R.S.
Department of Study
Microbiology
Discipline
Microbiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Language
eng
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.
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