Structure of the Michaelis complex and function of the catalytic center in the reductive half-reaction of computational and synthetic models of sulfite oxidase.
By using frontier-molecular-orbital and electrostatic (nucleophilic) interactions as well as relaxed potential-energy surface scans, it is shown that the initial step in the oxygen-atom transfer (OAT) reaction of [Mo(VI)O2-(S2C2Me2)SMe](-1) (1) and [Mo(VI)O2-{(S2C2(CN)2}2]2- (2) with HSO3(-) takes place by oxoanionic binding of the substrate to the Mo(VI) center with the formation of a stable Michaelis complex. The gas-phase and solvent-corrected enthalpy profile with fully optimized minima and transition states for the OAT reaction of 1 and 2 with HSO3(-) showed the release of reaction energy for both complexes. The optimized geometries of 1 and 2 in the respective enzyme-substrate complexes showed a common feature with the participation of hydrogen bonding of the substrate with the axial (spectator) oxo group in the subsequent formation of the six-membered MoO2HOS transition state. The enzyme-substrate complex of 2 shows heptacoordination as proposed earlier, although the trans (to axial oxo)-Mo-S(dithiolene) bond is elongated to 2.948 A.
Pal
Kuntal
K
Department of Chemistry, Indian Institute of Technology, Kanpur, Kanpur 208016, India.
Chaudhury
Pradeep K
PK
Sarkar
Sabyasachi
S
D001665:Binding Sites; D032701:Biomimetics; D002384:Catalysis; D020134:Catalytic Domain; D006860:Hydrogen Bonding; D008958:Models, Molecular; D010084:Oxidation-Reduction; D050876:Sulfite Oxidase / Q000737:chemistry*; D013456:Sulfur Acids
D013456:Sulfur Acids; D050876:Sulfite Oxidase