Interactions of 77Se and 13CO with nickel in the active site of active F420-nonreducing hydrogenase from Methanococcus voltae.

The selenium-containing F420-nonreducing hydrogenase from Methanococcus voltae was prepared in the Nia(I) middle dotCO state. The effect of illumination on this light-sensitive species was studied. EPR studies were carried out with enzyme containing natural selenium or with enzyme enriched in 77Se. Samples were prepared with either CO or 13CO. In the Nia(I) middle dotCO state, the nuclear spins of both 77Se (I = 1/2) and 13C (I = 1/2) interacted with the nickel-based unpaired electron, suggesting that they are positioned on opposite sites of the nickel ion. In the light-induced signal, the interaction with 13CO was lost. The 77Se nuclear spin introduced an anisotropic hyperfine splitting in both the dark and light-induced EPR signals. The data on the active enzyme of M. voltae are difficult to reconcile with the crystal structure of the inactive hydrogenase of Desulfovibrio gigas (Volbeda, A., Charon, M. H., Piras, C., Hatchikian, E. C., Frey, M., and Fontecilla Camps, J. C. (1995) Nature 373, 580-587) and suggest a structural change in the active site upon activation of the enzyme.