Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple

Published

February 1, 2001

Author(s)

I Spasojevic, I Batinic-Haberle, R D. Stevens, P Hambright, A N. Thorpe, J Grodkowski, Pedatsur Neta, I Fridovich

Abstract

A manganese(III) complex of biliverdin IX dimethyl ester, Mn^IIIBVDME}₂ was prepared and characterized by elemental analysis, uv/vis spectroscopy, cyclic voltammetry, chronocoulometry, electrospray mass spectrometry, freezing-point depression, magnetic susceptibility, and catalytic dismuting of superoxide anion, O₂ ^-. In a dimeric conformation each trivalent manganese is bound to four pyrrolic nitrogens of one and to the enolic oxygen of another biliverdin dimethyl ester molecule. This type of coordination stabilizes the + 4 metal oxidation state, whereby the +3/+4 redox cycling of the manganese in aqueous medium was found to be at E_1/2 = + 0.45 V vs NHE. This potential allows the Mn(III)/Mn(IV) couple to efficiently catalyze the dismutation of O₂ ^- with the catalytic rate constant obtained by cytochrome c assay at pH 7.8 and 25 ^oC, k_cat = 5.0 x 10⁷ M^-1 s^-1. The fifth coordination site of the manganese is occupied by an enolic oxygen, which precludes binding of NO , thus enhancing the specificity of the metal center towards O₂ ^-. For the same reason the Mn^IIIBVDME}₂ is resistant to attack by H₂O₂. The compound also proved to be an efficient SOD mimic in vivo, facilitating the aerobic growth of SOD-deficient Escherichia coli.

Citation

Inorganic Chemistry

Volume

40

Issue

No. 4

Pub Type

Journals

Keywords

biliverdin, catalysis, kinetics, manganese, superoxide

Citation

Spasojevic, I. , Batinic-Haberle, I. , Stevens, R. , Hambright, P. , Thorpe, A. , Grodkowski, J. , Neta, P. and Fridovich, I. (2001), Manganese(III) Biliverdin IX Dimethyl Ester: A Powerful Catalytic Scavenger of Superoxide Employing the Mn(III)/Mn(IV) Redox Couple, Inorganic Chemistry (Accessed December 13, 2024)