INFLUENCE OF ILLUMINATION ON THE ELECTRONIC INTERACTION BETWEEN SE-77 AND NICKEL IN ACTIVE F420-NON-REDUCING HYDROGENASE FROM METHANOCOCCUS-VOLTAE

The selenium-containing F420-non-reducing hydrogenase from Methanococcus voltae was anaerobically purified. The enzyme as isolated showed an EPR spectrum with g(x,y,z) = 2.21, 2.15 and 2.01. Upon illumination this spectrum disappeared and a new signal with the lowest g value at 2.05 arose. EPR studies were carried out either with the enzyme containing natural selenium or enriched in the nuclear isotope Se-77. The hyperfine splitting caused by Se-77 in the 'dark' signal is shown to be highly anisotropic. In contrast the splitting is nearly isotropic after illumination. A new model for the nickel site is proposed to explain these observations.