Effect of Modified Hemes on the Spectral Properties and Activity of Manganese Peroxidase

Recombinant manganese peroxidase (rMnP), expressed inEscherichia colias apo-protein, was constituted with Fe(III) protoporphyrin IX, Fe(III) protoporphyrin IX dimethyl ester (DME), Fe(III) deuteroporphyrin (Deut), Fe(III) etioporphyrin III (Etio), and Fe(III) methylpyrrolporphyrin XXI (MPP). The electronic absorption spectra of these hemoproteins were similar to those of native MnP, but absorption maxima were shifted to longer wavelengths in the order of Deut-rMnP, MPP-rMnP, Etio-rMnP, DME-rMnP, andrMnP. All enzymes contained a high-spin, pentacoordinate heme iron as evidenced by the characteristic charge transfer bands in the visible region. The hemoproteins exhibited reduced catalytic activity while maintaining similar substrateKmvalues compared to native MnP. Compounds I, II, and III were obtained for these hemin-analogue enzymes except for Deut-rMnP. We concluded that the spectral properties of MnP are strongly influenced by porphyrin α- and β-meso edge substituents and manganese oxidation is affected by the γ-meso edge groups, suggesting a role for the heme propionates in electron transfer during catalysis.