Journal of Biological Inorganic Chemistry p. 1327 - 1341 (2015)
Update date:2022-08-22
Topics:
Kipouros, Ioannis
Fica-Contreras, Sebastian Matias
Bowe, Gregory Joon Kee
Choi, Sunhee
We previously reported that a Pt(IV) complex, [PtIV(dach)Cl4] [trans-d,l-1,2-diaminocyclohexanetetrachloroplatinum(IV)] binds to the N7 of 5′-dGMP (deoxyguanosine-5′-monophosphate) at a relatively fast rate and oxidizes it to 8-oxo-5′-dGMP. Here, we further studied the kinetics of the oxidation of 5′-dGMP by the PtIV complex. The electron transfer rate constants between 5′-dGMP and PtIV in [H8-5′-dGMP-PtIV] and [D8-5′-dGMP-PtIV] were similar, giving a small value of the kinetic isotope effect (KIE: 1.2 ± 0.2). This small KIE indicates that the deprotonation of H8 in [H8-5′-dGMP-PtIV] is not involved in the rate-determining step in the electron transfer between guanine (G) and PtIV. We also studied the reaction of 5′-dGDP (deoxyguanosine-5′-diphosphate) and 5′-dGTP (deoxyguanosine-5′-triphosphate) with the PtIV complex. Our results showed that [PtIV(dach)Cl4] oxidized 5′-dGDP and 5′-dGTP to 8-oxo-5′-dGDP and 8-oxo-5′-dGTP, respectively, by the same mechanism and kinetics as for 5′-dGMP. The PtIV complex binds to N7 followed by a two-electron inner sphere electron transfer from G to PtIV. The reaction was catalyzed by PtII and occurred faster at higher pH. The electron transfer was initiated by either an intramolecular nucleophilic attack by any of the phosphate groups or an intermolecular nucleophilic attack by free OH- in the solution. The rates of reactions for the three nucleotides followed the order: 5′-dGMP > 5′-dGDP > 5′-dGTP, indicating that the bulkier the phosphate groups are, the slower the reaction is, due to the larger steric hindrance and rotational barrier of the phosphate groups.
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