Science and Education Publishing American Journal of Medical and Biological Research 2328-4099 4 3 2016 8 6 Role of Some Metal Ions on Steady-state Kinetics of Engineered Wild-type and Manganese (II) Binding Site Mutants of Recombinant Phlebia radiata Manganese Peroxidase 3 (rPr-MnP3) 42 52 EN Usenobong F. Ufot Department of Biological Sciences, Akwa Ibom State University, P.M.B. 1167, Uyo, Akwa Ibom State, Nigeria Aniefiok E. Ite Idorenyin H. Usoh Monday I. Akpanabiatu AJMBR2016432 10.12691/ajmbr-4-3-2 2016 4 16 2016 7 14 2016 8 4 This study investigated the steady-state kinetics of engineered wild-type and manganese (II) binding site mutants of recombinant Phlebia radiata manganese peroxidase 3(rPr-MnP3). The effect (activation or inhibition) of some metal ions (Co2+, Zn2+ Cu2+ and Na+) on the activity of rPr-MnP3 enzymes was also studied. The results obtained showed that the rPr-MnP3 mutants in which the metal binding functionality has been largely lost have been created. Na+ (mono-valent ion) and Co2+showed similar characteristics by exhibiting stimulatory effects on the activity of wild-type rPr-MnP3. However, Cu2+ and Zn2+ had mixed inhibitory effects on wild-type and mutants (E40H, E44H, E40H/E44H). It was observed that Cu2+ was by far the strongest inhibitor of engineered rPr-MnP3 enzymes while Co2+ exhibited a non-competitive inhibitory effect on the double mutant (E40H/E44H) and D186H activities. In addition, Zn2+ and Cu2+also had non-competitive inhibitory effect on D186H mutant enzyme activity. The results obtained further showed that the competitive inhibitory effect of Cu2+observed in other rPr-MnP3 enzymes is largely removed in D186H mutant enzyme. Generally, histidine substitution retained a strong selectivity for Cu2+ as competitive inhibitor. Zn2+ being generally non-competitive suggest involvement of sites other than the Mn (II) binding site. This study showed that rPr-MnP3 enzymes function with alternate ligands in the Mn2+ binding site and does not have absolute obligate requirement for all carboxylate ligand set.