Substitution of a conserved catalytic dyad into 2-KPCC causes loss of carboxylation activity.

The characteristic His-Glu catalytic dyad of the disulfide oxidoreductase (DSOR) family of enzymes is replaced in 2-ketopropyl coenzyme M oxidoreductase/carboxylase (2-KPCC) by the residues Phe-His. 2-KPCC is the only known carboxylating member of the DSOR family and has replaced this dyad potentially to eliminate proton-donating groups at a key position in the active site. Substitution of the Phe-His by the canonical residues results in production of higher relative concentrations of acetone versus the natural product acetoacetate. The results indicate that these differences in 2-KPCC are key in discriminating between carbon dioxide and protons as attacking electrophiles.