EPR and ENDOR Studies of NiFe Hydrogenase: Contributions to Understanding the Mechanism of Biological Hydrogen Conversion

摘要

EPR experiments are performed on the paramagnetic intermediates of the enzymatic cycle of a [NiFe] hydrogenase in (frozen) solution and single crystals. For states Ni-A, Ni-B, Ni-C and Ni-L the g-tensor magnitudes and orientations were obtained. Pulse EPR and ENDOR techniques give information on the electron-nuclear hyperfme and nuclear quadrupole couplings. The data are compared with those derived from density functional calculations performed on a geometry-optimized model cluster for the active NiFe-center. Thereby detailed information of the electronic and geometrical structure of the intermediates is obtained. Based on these data a reaction mechanism is proposed for this enzyme.