EPR of a novel high‐spin component in activated hydrogenase from Desulfovibrio vulgaris (Hildenborough)

Abstract

The EPR of reoxidized hydrogenase from Desulfovibrio vulgaris (H.) has been reinvestigated. In contrast to other workers [(1984) Proc. Natl. Acad. Sci. USA 81, 3728-3732] we find the axial signal with g = 2.06; 2.01 to be only a minor component of concentration 0.03 . In the spectrum of fully active reoxidized enzyme this signal is overshadowed by a rhombic signal (0.1 ) with g = 2.11; 2.05; 2.00 reminiscent of the only signal found for other oxidized bidirectional hydrogenases. In addition, a novel signal has been detected with g _eff = 5.0 which, under the assumptions that S = 2 and ¦Δm _s¦= 2, quantitates to roughly one . Ethylene glycol affects the relative intensity of the different signals. It is suggested that O₂ sensitization parallels a spin-state transition of an iron-sulfur cluster.