Influence of the Catalytic Tryptophan Environment

The amino acid residues at the environment of the catalytic tryptophan described above (Fig. 3.6) could be responsible for the differences observed in the oxidation of high redox-potential aromatic substrates by VP and LiP. In this regard, LiP needs redox mediators for oxidation of some compounds that are directly oxidized by VP, such as Reactive Black 5 (RB5) and even polymeric lignin (although model dimers are directly oxidized) [10]. In contrast, VP exhibits a lower efficiency oxidizing VA than LiP. 

Conversely, it was demonstrated that three of the five exposed acidic residues around Trpl 71 in P. chrysosporium LiP affected the kinetics of VA oxidation [77] and suggested that a partially acidic environment would stabilize the VA cation radical to act as an enzyme-bond mediator [78]. Interestingly, the RB5-oxidizing activity was 

Finally, it could also be demonstrated that it is possible to improve VP catalytic properties by modifying the amino acid residues around the catalytic tryptophan. In this sense, simultaneous removal of Arg257 and incorporation of a phenylalanine residue, homologous to LiP Phe267 involved in VA binding [80], resulted in a VP variant with VA transient-state kinetic constants comparable to those of LiP [76]. 

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