The Role of Zinc Ion in the Active Site of Copper-Zinc Superoxide Dismutase

Abstract

The interaction of the superoxide radical ion O2– with the active site of Cu, Zn-superoxide dismutase is stud-ied by computer simulation using the ORCA software package version 5.0.2 at the level of density functional theory using the PBE functional and the basis sets of functions def2-SVP, def2-SVPD and def2-TZVPD. The main characteristics for two processes of electron transfer in the catalytic cycle of radical ion deactivation are obtained: reaction potential ΔG0, total reorganization energy λtot, activation energy ΔG≠, overlap matrix ele-ment HDA, and transfer rate constant k according to Marcus. The variable factor in the modeling is the pres-ence of the Zn2+ ion at the active site of the enzyme. Two variants of the electron transfer mechanism are con-sidered: one carried out through ligands and another occurring in the immediate vicinity of an oxygen-containing particle and a copper ion. It has been established that the presence of the Zn2+ ion contributes to a large extent only to the second electron transfer from the Cu+ ion to the protonated form of the radical ion, to the hydroperoxide radical HO2. Other things being equal, the zinc ion increases the electron transfer rate con-stant by five times through specific interactions.