Abstract
Recent work concerning the reaction mechanism of the molybdenum‐containing formate dehydrogenases is discussed, focusing on two alternate mechanisms of action for the enzyme involving either formation of CO
2
or bicarbonate as the immediate product of the reaction. On the basis of the pH dependence of the rate of reduction of enzyme by formate and the results of a recent GC/MS study undertaken under single‐turnover conditions indicating that no
18
O from solvent H
2
18
O is incorporated into product CO
2
, it is concluded that bicarbonate cannot be formed in the course of the reaction, and that cysteine, once dissociated from the molybdenum, cannot be functioning as a base in the course of the reaction.