Evolution of enzymatic activities in the orotidine 5'-monophosphate decarboxylase suprafamily: crystallographic evidence for a proton relay system in the active site of 3-keto-L-gulonate 6- phosphate decarboxylase

Structural and biochemical evidence suggest that the 3-keto-L-gulonate 6- phosphate decarboxylase (KGPDC) reaction proceeds via a Mg(super 2+)-stabilized 1,2-cis-enediolate intermediate. The catalytic roles of conserved residues in the active site of KGPDC is defined and demonstrated that even though KGPDC and orotidine 5'-monophosphate decarboxylase (OMPDC) share a common active site architecture, each enzyme uses this architecture to catalyze reactions with unrelated substrate specificity and unrelated reactions mechanisms.