Direct electron transfer catalysed by recombinant forms of horseradish peroxidase: insight into the mechanism

The paper presents the first results on recombinant horseradish peroxidase (HRP) electrochemistry obtained on graphite with a rotating disk electrode system. Recombinant MP demonstrates a higher percentage of properly oriente d molecules than the native enzyme. The first important conclusion based on the recombinant HRP electrochemistry is that glycosylation hinders direct electron transfer (ET). The single-point mutants with limited activity towa rd phenolic substrates, viz. Asn70Val and Asn70Asp showed no changes in the registered current upon the addition of p-cresol, catechol, p-aminophenol and guaiacol and, thus, in this particular case mediated ET was not more ad vantageous than direct ET. The rate constants for direct ET were comparable for all mutants tested in this study demonstrating that direct ET does not depend on the enzyme's ability or inability to oxidise phenolic substrates . The results obtained in this study demonstrate the true mediatorless natu re of enzyme-catalysed direct ET. (C) 1999 Elsevier Science S.A. All rights reserved.