Theoretical studies on magnetic interactions between Ni(II) ions in urease

The chemical species of bridge oxygen (WB) in active site of urease was examined in terms of a magnetic interaction between Ni(II) ions. The effective exchange integrals (J(ab)) values between Ni(II) ions were calculated by using three candidates of WB, i.e., H2O, OH- and O2-. The unrestricted hybrid density functional theory (UHDFT) calculations were carried out using the smallest models and realistic models. In the case of the smallest models, the experimental J(ab) value (-6.3 cm(-1)) was a middle value of WB = H2O (-2.6 cm(-1)) and WB = OH- (-11.4 cm(-1)), while we could not obtain appropriate electronic structure using O2--bridge model. The J(ab) became -16.7 cm(-1) by using more realistic OH-bridge model, while one spin density on Ni2 ion was delocalized to Asp360 in case of H2O-bridge model. Natural orbital analyses revealed that the magnetic orbital through Lys-bridge delocalized to Asp360 and it seemed to associate with the spin transfer. From the results, OH--bridge seemed to be the most possible candidate for the structure of active site in urease. (c) 2005 Elsevier Ltd. All rights reserved.