Channeling of carbon monoxide during anaerobic carbon dioxide fixation

Javier Seravalli, Stephen W. Ragsdale

Research output: Contribution to journalArticlepeer-review

66 Scopus citations


Carbon monoxide is an intermediate in carbon dioxide fixation by diverse microbes that inhabit anaerobic environments including the human colon. These organisms fix CO2 by the Wood-Ljungdahl pathway of acetyl-CoA biosynthesis. The bifunctional CO dehydrogenase/acetyl-CoA synthase (CODH/ACS) catalyzes several key steps in this pathway. CO2 is reduced to CO at a nickel iron- sulfur cluster called cluster C located in the CODH subunit. Then, CO is condensed with a methyl group and coenzyme A at cluster A, another nickel iron-sulfur cluster in the ACS subunit. Spectroscopic studies indicate that clusters A and C are at least 10-15 Å apart. To gain a better understanding of how CO production and utilization are coordinated, we have studied an isotopic exchange reaction between labeled CO2 and the carbonyl group of acetyl-CoA with the CODH/ACS from Clostridium thermoaceticum. When solution CO is provided at saturating levels, only CO2-derived CO is incorporated into the carbonyl group of acetyl-CoA. Furthermore, when high levels of hemoglobin or myoglobin are added to remove CO from solution, there is only partial inhibition of the incorporation of CO2-derived CO into acetyl-CoA. These results provide strong evidence for the existence of a CO channel between cluster C in the CODH subunit and cluster A in the ACS subunit. The existence of such a channel would tightly couple CO production and utilization and help explain why high levels of this toxic gas do not escape into the environment. Instead, microbes sequester this energy-rich carbon source for metabolic reactions.

Original languageEnglish (US)
Pages (from-to)1274-1277
Number of pages4
Issue number6
StatePublished - Feb 15 2000

ASJC Scopus subject areas

  • Biochemistry

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