Mechanistic enzymology of CO dehydrogenase from Clostridium thermoaceticum. Progress report, March 25, 1993--March 24, 1994

Abstract

Anaerobic acetogenic bacteria can convert carbon dioxide and carbon monoxide to cell carbon by a pathway which is called the acetyl-CoA pathway. With this pathway they convert monosaccharides and the methoxy group of lignin derived aromatics into acetic acid. The acetic acid is then used by a number of organisms, including methanogens, as a carbon and energy source. Therefore, the acetyl-CoA pathway links the biodegradation of complex macromolecules like cellulose and lignin to the utilization of simple two carbon units. The final steps in acetyl-CoA biosynthesis by anaerobic bacteria are performed by carbon monoxide dehydrogenase (CODH), a nickel/iron-sulfur protein. We have previously demonstrate that the conversion of CH{sub 3}-H{sub 4} folate, CO and CoA to acetyl-CoA involves enzyme-bound intermediates that the one- and two-carbon precursors of acetyl-CoA are organometallic complexes, and that the site for assembly of acetyl-CoA is a novel Ni-Fe-S cluster which binds CO as a terminal carbonyl, i.e., M-C {equivalent_to} O. In the past year we have shown that the activities for CO oxidation and acetyl-CoA synthesis sites occur at separate sites, that it is a Fe, not a Ni, site in the Ni-Fe-S cluster which binds CO for acetyl-CoA synthesis, and that carbon disulfide (CS2) reactsmore » with CODH at the Ni-Fe-S site to generate an isolated Ni(I) species. We also determined that CS{sub 2} is competitive with CO at the acetyl-CoA synthesis site and does not bind to the CO oxidation/CO{sub 2} reduction site.« less