Versatile peroxidases (VPs) are glycoproteins produced as several isoenzymes were first described in 1996 by Martinez et al. (1996) and later were characterized in fungus, P eryngii (Ruiz-Duenas et al. 1999), a fungus known for selective degradation of lignin. They were further isolated from other fungal spp., P. ostreatus, Pleurotus pulmonarius, and Bjerkandera adusta (Hemfling et al. 1998a, b, c; Mester and Field 1998; Ruiz-Duenas et al. 2001). Versatile peroxidases exhibit properties of both LiPs and MnPs and are able to oxidize Mn2+ to Mn3+ like manganese peroxidases and degrade non-phenolic lignin like laccases (Sigoillot et al. 2012).
Other Lignin-Degrading Enzymes and Accessory Enzymes
Accessory ligninolytic enzymes include oxidases that produce hydrogen peroxide which is required by peroxidases, and mycelium-associated dehydrogenases, which reduce lignin-derived compounds (Martinez et al. 2005). Examples of such enzymes include glyoxal oxidase (GLOX, a copper-radical protein) found in P. chrysospo- rium and aryl-alcohol oxidase (AAO) found in P. eryngii (Kersten 1990; Guillen et al. 1992). Other accessory enzymes include aryl-alcohol dehydrogenases (AAD) (a flavoprotein) and quinone reductases (QR) which are produced from fungi used for lignin degradation (Guillen et al. 1997). In addition, it has also been reported that cellobiose dehydrogenase (CDH), commonly used for cellulose degradation is also involved in lignin degradation in the presence of hydrogen peroxide and chelated iron ions (Henriksson et al. 1995). CDH reduces the quinones which can be directly used by lignin-degrading enzymes or supports manganese peroxidase reaction (Henriksson et al. 2000). The challenge with ligninolytic enzymes is that they are not produced in large quantities and they are too bulky to penetrate the plant cell walls.