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Applied and Environmental Microbiology, January 2000, p. 170-175, Vol. 66, No. 1
Centro de Investigaciones Biológicas,
Consejo Superior de Investigaciones Científicas, E-28006
Madrid, Spain
Received 20 August 1999/Accepted 28 October 1999
Oxygen activation during oxidation of the lignin-derived
hydroquinones 2-methoxy-1,4-benzohydroquinone (MBQH2) and
2,6-dimethoxy-1,4-benzohydroquinone (DBQH2) by laccase from
Pleurotus eryngii was examined. Laccase oxidized
DBQH2 more efficiently than it oxidized MBQH2;
both the affinity and maximal velocity of oxidation were higher for
DBQH2 than for MBQH2. Autoxidation of the
semiquinones produced by laccase led to the activation of oxygen,
producing superoxide anion radicals (Q·
0099-2240/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Oxygen Activation during Oxidation of
Methoxyhydroquinones by Laccase from Pleurotus
eryngii
+ O2 
Q + O2·). As this
reaction is reversible, its existence was first noted in studies of the
effect of systems consuming and producing
O2· on quinone formation rates. Then, the
production of H2O2 in laccase reactions, as a
consequence of O2· dismutation, confirmed
that semiquinones autoxidized. The highest H2O2
levels were obtained with DBQH2, indicating that
DBQ· autoxidized to a greater extent than did
MBQ·. Besides undergoing autoxidation, semiquinones
were found to be transformed into quinones via dismutation and laccase
oxidation. Two ways of favoring semiquinone autoxidation over
dismutation and laccase oxidation were increasing the rate of
O2· consumption with superoxide dismutase
(SOD) and recycling of quinones with diaphorase (a reductase catalyzing
the divalent reduction of quinones). These two strategies made the
laccase reaction conditions more natural, since
O2·, besides undergoing dismutation, reacts
with Mn2+, Fe3+, and aromatic radicals. In
addition, quinones are continuously reduced by the mycelium of
white-rot fungi. The presence of SOD in laccase reactions increased the
extent of autoxidation of 100 µM concentrations of
MBQ· and DBQ· from 4.5 to 30.6% and
from 19.6 to 40.0%, respectively. With diaphorase, the extent of
MBQ· autoxidation rose to 13.8% and that of
DBQ· increased to 39.9%.
*
Corresponding author. Mailing address: Centro de
Investigaciones Biológicas, Consejo Superior de Investigaciones
Científicas, Velázquez 144, E-28006 Madrid, Spain. Phone:
34 915611800. Fax: 34 915627518. E-mail:
guillen{at}cib.csic.es.
Applied and Environmental Microbiology, January 2000, p. 170-175, Vol. 66, No. 1
0099-2240/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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