Influence of illumination on the electronic interaction between 77Se 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 gx,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 77Se. The hyperfine splitting caused by 77Se 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.