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Applied and Environmental Microbiology, May 2000, p. 2052-2056, Vol. 66, No. 5
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Redox Chemistry in Laccase-Catalyzed Oxidation of N-Hydroxy Compounds

Feng Xu,^1,* Juozas J. Kulys,^2,* Kyle Duke,¹ Kaichang Li,³ Kastis Krikstopaitis,² Heinz-Josef W. Deussen,⁴ Eric Abbate,¹ Vilija Galinyte,² and Palle Schneider^4,*

Novo Nordisk Biotech, Davis, California 95616¹; Institute of Biochemistry, Mokslininku 12, 2600 Vilnius, Lithuania²; Department of Forest Products, Oregon State University, Corvallis, Oregon 97331³; and Novo Nordisk A/S, Novo Allé, DK-2880 Bagsværd, Denmark⁴

Received 15 November 1999/Accepted 8 February 2000

1-Hydroxybenzotriazole, violuric acid, and N-hydroxyacetanilide are three N-OH compounds capable of mediating a range of laccase-catalyzed biotransformations, such as paper pulp delignification and degradation of polycyclic hydrocarbons. The mechanism of their enzymatic oxidation was studied with seven fungal laccases. The oxidation had a bell-shaped pH-activity profile with an optimal pH ranging from 4 to 7. The oxidation rate was found to be dependent on the redox potential difference between the N-OH substrate and laccase. A laccase with a higher redox potential or an N-OH compound with a lower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other redox-active compounds, an "outer-sphere" type of single-electron transfer from the substrate to laccase and proton release are speculated to be involved in the rate-limiting step for N-OH oxidation.

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^* Corresponding author. Mailing address for Feng Xu: Novo Nordisk Biotech, 1445 Drew Ave., Davis, CA 95616. Phone: (530) 757-8100. Fax: (530) 758-0317. E-mail: fengxu{at}nnbt.com. Mailing address for Juozas J. Kulys: Institute of Biochemistry, Mokslininku 12, 2600 Vilnius, Lithuania. Phone: 370-2-729176. Fax: 370-2-729196. E-mail: jkulys{at}bchi.lt. Mailing address for Palle Schneider: Novo Nordisk A/S, Novo Allé, 6BS.99, DK-2880 Bagsværd, Denmark. Phone: 45-44422261. Fax: 45-44422202. E-mail: ps{at}novo.dk.

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Applied and Environmental Microbiology, May 2000, p. 2052-2056, Vol. 66, No. 5
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

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