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J. Biol. Chem., Vol. 278, Issue 30, 27432-27438, July 25, 2003

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Reactions of Manganese Porphyrins with Peroxynitrite and Carbonate Radical Anion^*

Gerardo Ferrer-Sueta  , Darío Vitturi  ¶, Ines Batini-Haberle || **, Irwin Fridovich || , Sara Goldstein , Gidon Czapski  and Rafael Radi ¶¶ ||||

From the Laboratorio de Fisicoquímica Biológica, Facultad de Ciencias, Universidad de la República, Montevideo 11400, Uruguay, ^||Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, Department of Physical Chemistry, The Hebrew University, Jerusalem 91904, Israel, and ^¶¶Departamento de Bioquímica, Facultad de Medicina, Universidad de la República, Av. Gral. Flores 2125, Montevideo 11800, Uruguay

We have studied the reaction kinetics of ten manganese porphyrins, differing in their meso substituents, with peroxynitrite (ONOO^–) and carbonate radical anion () using stopped-flow and pulse radiolysis, respectively. Rate constants for the reactions of Mn(III) porphyrins with ONOO^– ranged from 1 x 10⁵ to 3.4 x 10⁷ M^–1 s^–1 and correlated well with previously reported kinetic and thermodynamic data that reflect the resonance and inductive effects of the substituents on the porphyrin ring. Rate constants for the reactions of Mn(III) porphyrins with ranged from 2 x 10⁸ to 1.2 x 10⁹ M^–1s^–1 at pH 8.5 and increased with pH as a consequence of the ionization of the complexes. Mn(II) porphyrins reacted with with rate constants ranging from 1 x 10⁹ to 5 x 10⁹ M^–1s^–1 at pH 10.4. Hence, fast scavenging of ONOO^– and by manganese porphyrins could occur in vivo because of the catalytic reduction at the expense of a number of cellular reductants. Additionally, we determined the pK_a of the axial water molecules of the Mn(III) complexes at pH 7.5–13.2 by spectrophotometric titration. Results were consistent with two acid-base equilibria for most of the complexes studied. The pK_a values also correlated with the resonance and inductive effects of the substituents. The correlations of E with the rate constants with ONOO^– and with the pK_a values display a deviation from linearity when N-alkylpyridinium substituents included N-alkyl moieties longer than ethyl, which is interpreted in terms of a decrease in the local dielectric constant.

Received for publication, December 31, 2002 , and in revised form, April 15, 2003.

^* This work was supported in part by grants from the International Centre for Genetic Engineering and Biotechnology (Italy), The Howard Hughes Medical Institute (to R. R.), and by Comisión Sectorial de Investigación Científica (CSIC, Uruguay) (to G. F. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received travel grants from Programa de Desarrollo de Ciencias Básicas and CSIC to visit the Hebrew University, Jerusalem, Israel.

^¶ Received a young researcher scholarship from CSIC.

^** Recipient of Christopher Reeve Paralysis Foundation Grant BA1-0103-1 and supported in part by Aeolus/Incara.

Recipient of National Institutes of Health Grant R01DK59868 and supported in part by the Amyotrophic Lateral Schlerosis Association.

^|||| International Research Scholar of the Howard Hughes Medical Institute. To whom correspondence should be addressed. Tel.: 5982-9249561; Fax: 5982-9249563; E-mail: rradi{at}fmed.edu.uy.

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