Catalytic Properties of Tryptophanless Recombinant Horseradish Peroxidase

O. V. Ignatenko¹, I. G. Gazaryan¹, E. A. Mareeva¹, T. A. Chubar¹, V. A. Fechina², P. A. Savitsky¹, A. M. Rojkova¹, and V. I. Tishkov^1*

IGNATENKO et al.

¹Department of Chemical Enzymology, School of Chemistry, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (7-095) 939-2742; E-mail: vit@enz.chem.msu.ru

²Bach Institute of Biochemistry, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 117071 Russia; fax: (7-095) 954-2732; E-mail: inbio@glas.acp.org

^* To whom correspondence should be addressed.

Received July 5, 1999; Revision received January 20, 2000

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Heme-containing plant peroxidases (EC 1.11.1.7) contain a highly conserved single tryptophan residue. Its replacement with Phe in recombinant horseradish peroxidase (rHRP) increased the stability of the mutant enzyme in acid media. The kinetic properties of native, wild-type, and W117F mutant recombinant horseradish peroxidase in the reactions of ammonium 2,2´-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), guaiacol, and o-phenylenediamine oxidation are very similar. However, significant changes in the reaction rate constant characteristic for the monomolecular rate-limiting step ascribed either to product dissociation from its complex with the enzyme or electron transfer from the substrate to the active site within the Michaelis complex were observed. The data indirectly indicate the participation of the single Trp residue in oxidation of ABTS and guaiacol and possible differences in kinetic mechanisms for oxidation of ABTS, guaiacol, and o-phenylenediamine.

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KEY WORDS: horseradish peroxidase, site-directed mutagenesis, Trp-117Phe, refolding, pH-stability, steady-state kinetics, elementary step rate constants

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