Lignin Peroxidases (LiP) (1,2-Bis-(3,4-dimethoxyphenyl)- propane-l, 3-diol/Hydrogen Peroxide Oxidoreductases, EC 184.108.40.206)
LiPs were first discovered in P. chrysosporium in the mid-1980s and are considered as true ligninases as they directly catalyze lignin oxidation. They are glycosylated extracellular enzymes that are glycosylated (up to 20-30 %) and monomeric and contain one ferric protoheme IX per molecule. Several isoforms and isoenzymes are present in fungal secretomes (Sigoillot et al. 2012). LiPs act on lignin through low- molecular-weight redox chemical mediators. When fungi P. chrysosporium act on lignin, it produces LiP and veratyl alcohol (VP) (Fenn and Kent Kirk 1981), LiP then oxidizes LiP, forming a radical cation that degrades lignin as a diffusible redox mediator. VA is unstable in cation form and thus its role as diffusible mediator is questionable. However, its major role is to protect inactivation of LiP by hydrogen peroxide (Sigoillot et al. 2012).
Manganese Peroxidases (MnP) (Mn (ll)/Hydrogen Peroxide Oxidoreductases, EC 220.127.116.11
MnPs were discovered in the mid-1980s in P. chrysosporium as MnP isoenzymes and are considered as true ligninases because of high redox potential (Glenn et al. 1983; Kuwahara et al. 1984). MnPs are described as extracellular glycosylated enzymes that contain one ferric protoheme IX per molecule. The desired temperature for their maximal activity ranges between 30 and 40 °C. Manganese peroxidases use Mn(II) as their reducing substrate to form Mn(III) and oxidize a variety of monomeric phenols present in lignin. Manganese peroxidases are observed in the white-rot fungi and are able to cleave Ca-Cp and p-aryl ether bonds by indirect oxidation through the peroxidation of non-phenolic lignin models (Martinez et al. 2005), but their action on lignin degradation has not been clearly demonstrated. The major drawback in commercial applications of manganese peroxidases is the enzyme produced in low quantities; but that problem can be solved with the use of DNA recombinant technology (Xu et al. 2010).