STABILIZATION OF LIGNIN PEROXIDASES IN WHITE-ROT FUNGI BY TRYPTOPHAN

Supplementation of various cultures of white rot fungi with tryptophan was found to have a large stimulatory effect on lignin peroxidase act ivity levels. This enhancement was greater than that observed in the p resence of the lignin peroxidase recycling agent veratryl alcohol. Usi ng reverse transcription-PCR, we found that tryptophan does not act to induce lignin peroxidase expression at the level of gene transcriptio n. Instead, the activity enhancement observed is likely to result from the protective effect of tryptophan against H2O2 inactivation. In exp eriments using a partially purified lignin peroxidase preparation, try ptophan and its derivative indole were determined to function in the s ame way as veratryl alcohol in converting compound II, an oxidized for m of Lignin peroxidase, to ferric enzyme, thereby completing the catal ytic cycle. Furthermore, tryptophan was found to be a better substrate for lignin peroxidase than veratryl alcohol. Inclusion of either tryp tophan or indole enhanced the oxidation of the azo dyes methyl orange and Eriochrome blue black. Stimulation of azo dye oxidations by veratr yl alcohol has previously been shown to be due to its enzyme recycling function. Our data allow us to propose that tryptophan stabilizes lig nin peroxidase by acting as a reductant for the enzyme.