Nickel-deficient carbon monoxide dehydrogenase from Rhodospirillum rubrum: in vivo and in vitro activation by exogenous nickel

An inactive, Ni-deficient form of carbon monoxide (CO) dehydrogenase designated apo-CO dehydrogenase, accumulated in Rhodospirillum rubrum when cells were grown in the absence of Ni and treated with CO. In vivo, both CO dehydrogenase activity and hydrogenase activity increased several hundred fold upon addition of 2 μM NiCl2. Apo-CO dehydrogenase was purified to homogeneity and differed from holo-CO dehydrogenase only in its activity and Ni content, containing <0.2 mol of Ni per mol of protein, and a specific activity of 35 μmol of CO per min per mg. Optimal in vitro activation of purified apo-CO hydrogenase resulted in an enzyme with a specific activity of 2640 μmol of CO per min per mg. No additional enzymes or low molecular weight cofactors were required for activation. Apo-CO dehydrogenase was not activated by MgCl2, MnCl2, CuCl2, ZnCl2, CoCl2, or Na2MoO4. 63Ni was incorporated into apo-CO dehydrogenase during activation. The electron paramagnetic resonance (EPR) spectra of dithionite-reduced apo- and holo-enzyme were identical, indicating that, in the reduced state, the Fe-S centers observed by EPR are unchanged in the apo-enzyme