Biology Reference
In-Depth Information
Fig. 5. Structure of laccase (PDB
1KYA
;
Bertrand et al., 2002
) showing in (A) the
trinuclear copper centre (T2 and T3 coppers) and the single copper T1 and in (B) the
trinuclear centre forming a hole allowing dioxygen binding.
copper has a characteristic absorbance at 610 nm, responsible for the blue
colour of the enzyme.
The type-2 Cu, coordinated with two histidines and the two type-3 Cu,
each coordinated to three histidines, are arranged in a tri-nuclear centre. This
centre allows the fixation and reduction of dioxygen (
Fig. 5
B), which is the
final electron acceptor of the enzyme. Type-2 Cu shows no absorbance in the
visible range, although type-3 Cu has an absorption peak at 330 nm. Lac-
cases are generally classified into three groups according to the redox poten-
tial of the type-1 copper centre: low (ca. 0.4-0.5 V), medium (ca. 0.5-0.6 V)
and high (ca. 0.7-0.8 V) (
Xu et al., 1996
). C. cinereus and M. thermophila
laccases belong to the low potential group, while Scytalidium thermophilum
