IDENTIFICATION OF A CYSTEINE INVOLVED IN THE INTERACTION BETWEEN CARBON-MONOXIDE DEHYDROGENASE AND CORRINOID FE-S PROTEIN FROM CLOSTRIDIUM-THERMOACETICUM

In Clostridium thermoaceticum, the synthesis of acetyl-CoA from methyl tetrahydrofolate occurs via a series of enzymatic reactions involving methyl transferase, corrinoid/Fe-S protein (corrinoid), carbon monoxide dehydrogenase (CODH) and ferredoxin. We have investigated the PossibilitY of one or more of these proteins existing as multi-enzyme complexes in vivo with higher catalytic activity. A protein complex consisting of CODH and corrinoid was isolated from the cell-free extracts of Clostridium thermoaceticum. The acetyl-CoA synthesis was found to be approximately 1.8-fold higher with the complex than that observed with the isolated protein components. HPLC gel filtration analyses of the native and DTE reduced complex suggested that the CODH:corrinoid complex is held together primarily by an inter disulfide bond. By differential labeling of thiols with [C-14]N-ethylmaleimide it was found that Cys-506 of the alpha subunit of CODH was involved in the disulfide linkage with the corrinoid of the complex.