Bacterial Enzymes and Multi-enzymatic Systems for Cleaning-up Dyes from the Environment - Microbial Degradation of Synthetic Dyes in Wastewaters - page 44

Table 2 Steady-state apparent catalytic constants of puri ed recombinant PpDyP and BsDyP
(Santos et al. 2014 )
Substrates PpDyP BsDyP

V max
(U mg − 1 )

K m app
(

k cat /K m
(M − 1 s − 1 )

V max
(U mg − 1 )

K m app
(

k cat /K m
(M − 1 s − 1 ) ʼ M) ʼ M)

AQ dyes
Reactive
blue 5

2 × 10 5 5 × 10 4

15 ± 0.2 40 ± 3 11 ± 0.6 157 ± 46

Acid blue
62

10 5 10 4

14 ± 0.3 30 ± 4 2.4 × 12 ± 0.2 444 ± 45 2 ×

Azo dyes
Mordant
black 9

5 × 10 4 1 × 10 4 32 ± 0.2 320 ± 47 5 ± 0.1 385 ± 46

of DyPs (Liers et al. 2010 , 2011 ; Ahmad et al. 2011 ; Brown et al. 2012 ) and shows
a reasonable metalloxidase activity towards ferrous ions, not detected in the
Bacillus enzyme.
The different catalytic characteristics between members of the DyPs sub-families
point to distinct heme micro-environments. The UV-visible absorption spectra of
the Bs and Pp enzymes obtained upon addition of hydrogen peroxide reveal the
accumulation of different catalytic intermediates. The accumulation of compound I
in PpDyP is in accordance with results obtained for all other DyPs and the majority
of classical peroxidases, while the accumulation of compound II intermediate in
BsDyP was previously observed in A-type DypA from R. jostii RHA1 (Roberts
et al. 2011 ). The reasons behind the distinct spectral behaviour of BsDyP and
PpDyP are possibly related to the higher redox potential of BsDyP which con-
tributes to a relatively lower stability of Fe 3+ and thus to a lower stability of
compound I upon addition of hydrogen peroxide (Fig. 15 ). The poorer catalytic
activity of BsDyP, as compared to the Pp enzyme, must rely to a highly abundant

P ox + H 2 O 2 + H 2 O

Compound I (1)

+ +

AH A

Compound I Compound II (2)

+ + +

Compound II AH P ox A H 2 O (3)

Fig. 15 The three-step catalytic cycle in the classical peroxidation reaction catalyzed by
peroxidases, where P ox is the resting enzyme containing a ferric heme iron, Compound I is the rst
enzyme intermediate, which contains an oxyferryl iron center and a second oxidizing equivalent
stored as a radical (Fe(IV)=OR + ⦁ ) to give a formal oxidation state of +5, and Compound II is the
second enzyme intermediate in which the radical is discharged leaving only the oxyferryl iron
(formal oxidation state +4). AH represents the reducing substrate and A ⦁ the radical product