Substitution of Silver for Copper in the Binuclear Mo/Cu Center of Carbon Monoxide Dehydrogenase from Oligotropha carboxidovorans

Carbon monoxide dehydrogenase from Oligotropha carboxidovorans catalyzes the aerobic oxidation of carbon monoxide to carbon dioxide, providing the organism both a carbon source and energy for growth. The active site of the native enzyme is a unique binuclear molybdenum- and copper-containing center. Here we show that silver can be substituted for copper in the active site to yield a functional enzyme. The characteristic hyperfine coupling of the I = 1/2 nucleus of Ag is evident in the EPR signal of the binuclear active site observed upon reduction with CO, indicating both the incorporation of silver into the active site and, remarkably, retention of the catalytic activity. The silver-substituted enzyme is reduced by CO with an observed limiting rate constant of 8.1 s(-1), which can be compared with the value of 51 s(-1) for the wild-type enzyme. Steady-state kinetics for the Ag-substituted enzyme yielded k(cat) = 8.2 s(-1) and K(m) = 2.95 mu M at pH 7.2.