Composition and Catalase-Like Activity of Mn(II)-Bicarbonate Complexes

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K. G. Tikhonov, O. M. Zastrizhnaya, Yu. N. Kozlov, and V. V. Klimov^*

Institute of Basic Biological Problems, Russian Academy of Sciences, Institutskaya ul. 2, 142290 Pushchino, Moscow Region, Russia; fax: (4967) 330-532; E-mail: klimov@issp.serpukhov.su

^* To whom correspondence should be addressed.

Received May 18, 2006; Revision received June 16, 2006

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The composition and catalase-like activity of Mn²⁺ complexes with bicarbonate were investigated with voltammetry and kinetic methods (by the rate of O₂ production from H₂O₂). Three linear sections were revealed on the dependence of the reduction potential of Mn²⁺ on logarithm of bicarbonate concentration (logC_NaHCO3) having slopes equal to 0 mV/logC_NaHCO3, -14 mV/logC_NaHCO3, and -59 mV/logC_NaHCO3, corresponding to Mn²⁺ aqua complex (Mn²⁺_aq) and to Mn²⁺-bicarbonate complexes of the composition [Mn²⁺(HCO₃^-)]⁺ (at concentration of HCO₃^- 10-100 mM) and [Mn²⁺(HCO₃^-)₂]⁰ (at concentration of HCO₃^- 100-600 mM). Comparison of HCO₃^- concentration needed for the catalase-like activity of Mn²⁺ with the electrochemical data showed that only electroneutral complex Mn²⁺(HCO₃^-)₂ catalyzed decomposition of H₂O₂, whereas positively charged Mn²⁺_aq complex and [Mn²⁺(HCO₃^-)]⁺ were not active. The catalase-like activity of Mn²⁺ did not appear upon substitution of anions of carbonic acids (acetate and formate) for HCO₃^-. The rate of O₂ production in the system Mn²⁺-HCO₃^--H₂O₂ (pH 7.4) is proportional to the second power of Mn²⁺ concentration and to the fourth power of HCO₃^- concentration that indicates simultaneous involvement of two Mn²⁺(HCO₃^-)₂ complexes in the reaction of H₂O₂ decomposition.

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KEY WORDS: manganese, bicarbonate, hydrogen peroxide, catalase activity

DOI: 10.1134/S0006297906110137

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