L-edge X-ray magnetic circular dichroism of Ni enzymes: direct probe of Nispin states

X-ray magnetic circular dichroism (XMCD) measures the inner shell absorptio n difference between left and right circularly polarized X-rays in the pres ence of magnetic field, and provides us a direct probe of the spin values l ocalized in the specific metal sites. In this study, using Desulfovibrio de sulfuricans and Desulfovibrio gigas hydrogenases as examples, we have measu red the L-edge XMCD of Ni enzymes for the first time and analyzed them in c omparison with a doped high spin Ni-II model complex. The reduced hydrogena ses have a non-zero XMCD effect, which is consistent with a 'high spin' Ni- II site. The magneto-optical sum rules have also been used to derive the or bital and spin angular momentum. (C) 2001 Elsevier Science B.V. All rights reserved.