The nickel site in active Desulfovibrio baculatus [NiFeSe] hydrogenase is diamagnetic. Multifield saturation magnetization measurement of the spin state of Ni(II)

The magnetic properties of the nickel(II) site in active Desulfovibrio baculatus (DSM 1743) [NiFeSe] hydrogenase have been measured using the multifield saturation magnetization technique. The periplasmic [NiFeSe] hydrogenase was isolated from bacteria grown in excess selenium in the presence of ⁵⁷Fe. Saturation magnetization data were collected at three fixed fields (1.375, 2.75, 5.5 tesla) over the temperature range from 2 to 100 K. Mossbauer and EPR spectroscopies were used to characterize the magnetic state of the two [4Fe-4S] clusters of the enzyme and to quantitate the small amounts of iron impurities present in the sample. The nickel(II) site was found to be diamagnetic (low spin, S = 0). In combination with recent results from extended x-ray absorption fine structure studies, this magnetic state indicates that the nickel(II) site of active D. baculatus [NiFeSe] hydrogenase is five-coordinate.