Interactions of Se-77 and (CO)-C-13 with nickel in the active site of active F-420-nonreducing hydrogenase from Methanococcus voltae

The selenium-containing F-420-nonreducing hydrogenase from Methanococcus voltae was prepared in the Ni-a(I). CO 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 Se-77. Samples were prepared with either CO or (CO)-C-13. In the Ni-a(I). CO state, the nuclear spins of both Se-77 (I = 1/2) and C-13 (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 (CO)-C-13 was lost. The Se-77 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.