THE CENTRAL METABOLIC PATHWAY FROM ACETYL-COA TO BUTYRYL-COA IN CLOSTRIDIUM-ACETOBUTYLICUM

The pathway from acetyl-CoA to butyryl-CoA serves as a major carbon metabolism channel in Clostridium acetobutylicum and other butyrate-forming clostridia, and the steps are similar to those involved in fatty acid metabolism. Recent findings are discussed, reviewing the isolation and characterization of the enzymes of the pathway, and the analyses of metabolic intermediate levels and possible points of regulation of enzyme activity by CoA compounds. DNA analyses have identified the genes for two thiolase proteins, and an apparent operon encoding five proteins involved in the conversion of acetoacetyl-CoA to butyryl-CoA. These five proteins are beta-hydroxybutyryl-CoA dehydrogenase, crotonase, butyryl-CoA dehydrogenase and the alpha and beta subunits of an electron transfer flavoprotein.