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Appl. Environ. Microbiol., 07 1997, 2543-2548, Vol 63, No. 7
PJ Collins, JA Field, P Teunissen and AD Dobson
Supplementation of various cultures of white rot fungi with tryptophan was
found to have a large stimulatory effect on lignin peroxidase activity
levels. This enhancement was greater than that observed in the presence of
the lignin peroxidase recycling agent veratryl alcohol. Using reverse
transcription-PCR, we found that tryptophan does not act to induce lignin
peroxidase expression at the level of gene transcription. Instead, the
activity enhancement observed is likely to result from the protective
effect of tryptophan against H2O2 inactivation. In experiments using a
partially purified lignin peroxidase preparation, tryptophan and its
derivative indole were determined to function in the same way as veratryl
alcohol in converting compound II, an oxidized form of lignin peroxidase,
to ferric enzyme, thereby completing the catalytic cycle. Furthermore,
tryptophan was found to be a better substrate for lignin peroxidase than
veratryl alcohol. Inclusion of either tryptophan or indole enhanced the
oxidation of the azo dyes methyl orange and Eriochrome blue black.
Stimulation of azo dye oxidations by veratryl alcohol has previously been
shown to be due to its enzyme recycling function. Our data allow us to
propose that tryptophan stabilizes lignin peroxidase by acting as a
reductant for the enzyme.
Copyright © 1997, American Society for Microbiology
Stabilization of lignin peroxidases in white rot fungi by tryptophan
Microbiology Department, University College, Cork, Ireland.
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