2.1 Peroxidases
Peroxidases acting on lignin, including lignin peroxidases (LiPs), manganese peroxidases (MnPs), versatile peroxidases (VPs), and dye-peroxidases (DyPs), are the
most studied enzymes involved in the process of lignin degradation. Lignin
degrading peroxidases are mostly extracellular enzymes containing a heme prosthetic group in their active site (heme peroxidase superfamily) and require the
supplement of hydrogen peroxide (H 2 O 2 ) for their reactions (Fig. 3). These
enzymes make use of small molecules like veratryl alcohol (VA), in case of LiPs,
and unsaturated lipids (UL), in case of MnPs, as mediators for the depolymerization
of lignin [19, 20]. While LiPs, MnPs, and VPs are grouped into Class II superfamily
of heme peroxidases according to RedOxiBase [32], DyPs belong to a new family
with no similarities in primary and tertiary structures with the formers [21, 34].
Additional enzymes, namely lignin-degrading auxiliary enzymes, such as glyoxal
oxidase, aryl alcohol oxidase, or glucose dehydrogenase are necessary for degradation process through the oxidative generation of H 2 O 2 [21, 35].
2.1.1 Lignin Peroxidases (LiPs) (EC 1.11.1.14)
LiPs have a higher redox potential than most other enzymes, such as horseradish
peroxidase and laccases, and can oxidize non-phenolic aromatic substrates from
lignin in many cases without the need for a mediator. The enzyme was first discovered in P. chrysosporium and later similar LiPs were found in other white-rot
fungi, including T. versicolor, P. radiata, and Bjerkandera sp., as well as in Proteobacteria (Acinetobacter sp. and Pseudomonas sp.) and Actinobacteria (Streptomyces sp., Norcadia sp., Rhodococcus sp., etc.) [21, 24, 36, 37]. The catalytic cycle
of LiP starts with the oxidation of the native ferric Fe(III) enzyme by H 2 O 2 to
Fig. 2 Enzymatic conversion routes of lignin to value-added products. nPL—non-phenolic lignin;
PL—phenolic lignin; VA—veratryl alcohol; UL—unsaturated lipids; Ph—phenolic compounds.
For further details please refer to [19, 33]
448
G.-S. Nguyen et al.
Peroxidases acting on lignin, including lignin peroxidases (LiPs), manganese peroxidases (MnPs), versatile peroxidases (VPs), and dye-peroxidases (DyPs), are the
most studied enzymes involved in the process of lignin degradation. Lignin
degrading peroxidases are mostly extracellular enzymes containing a heme prosthetic group in their active site (heme peroxidase superfamily) and require the
supplement of hydrogen peroxide (H 2 O 2 ) for their reactions (Fig. 3). These
enzymes make use of small molecules like veratryl alcohol (VA), in case of LiPs,
and unsaturated lipids (UL), in case of MnPs, as mediators for the depolymerization
of lignin [19, 20]. While LiPs, MnPs, and VPs are grouped into Class II superfamily
of heme peroxidases according to RedOxiBase [32], DyPs belong to a new family
with no similarities in primary and tertiary structures with the formers [21, 34].
Additional enzymes, namely lignin-degrading auxiliary enzymes, such as glyoxal
oxidase, aryl alcohol oxidase, or glucose dehydrogenase are necessary for degradation process through the oxidative generation of H 2 O 2 [21, 35].
2.1.1 Lignin Peroxidases (LiPs) (EC 1.11.1.14)
LiPs have a higher redox potential than most other enzymes, such as horseradish
peroxidase and laccases, and can oxidize non-phenolic aromatic substrates from
lignin in many cases without the need for a mediator. The enzyme was first discovered in P. chrysosporium and later similar LiPs were found in other white-rot
fungi, including T. versicolor, P. radiata, and Bjerkandera sp., as well as in Proteobacteria (Acinetobacter sp. and Pseudomonas sp.) and Actinobacteria (Streptomyces sp., Norcadia sp., Rhodococcus sp., etc.) [21, 24, 36, 37]. The catalytic cycle
of LiP starts with the oxidation of the native ferric Fe(III) enzyme by H 2 O 2 to
Fig. 2 Enzymatic conversion routes of lignin to value-added products. nPL—non-phenolic lignin;
PL—phenolic lignin; VA—veratryl alcohol; UL—unsaturated lipids; Ph—phenolic compounds.
For further details please refer to [19, 33]
448
G.-S. Nguyen et al.