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Peroxidases, one of the key antioxidant enzymes, are widely distributed in nature and catalyze oxidation of various electron donor substrates concomitant with the decomposition of H 2 O 2. The non-animal plant peroxidases (class III peroxidase) are involved in various essential physiological processes of plant growth and development throughout their life cycle. In view of the capability of peroxidases to catalyze the redox reaction for a wide range of substrates, they are considered as one of the important enzyme from the point of view of their various medicinal, biochemical, immunological, biotechnological and industrial applications. They have been successfully used for biopulping and biobleaching in the paper and textile industries. Peroxidases have also been used in organic synthesis, bioremediation, as well as various analytical applications in diagnostic kits, ELISA. Peroxidase based biosensors find application in analytical systems for determination of hydrogen peroxide, glucose, alcohols, glutamate, and choline etc. Thus, in view of array of physiological functions as well as industrial applications, the peroxidases have conquered a dominant position in research groups and become one of the most extensively studied enzymes. In this direction, the present review embodies the classification, mechanism of action, major physiological functions as well as industrial applications of plant peroxidases.

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Laccase, widely distributed in bacteria, fungi, and plants, catalyzes the oxidation of wide range of compounds. With regards to one of the important physiological functions, plant laccases are considered to catalyze lignin biosynthesis while fungal laccases are considered for lignin degradation. The present study was undertaken to explain this dual function of laccases using in-silico molecular docking and dynamics simulation approaches. Modeling and superimposition analyses of one each representative of plant and fungal laccases, namely, Populus trichocarpa and Trametes versicolor, respectively, revealed low level of similarity in the folding of two laccases at 3D levels. Docking analyses revealed significantly higher binding efficiency for lignin model compounds, in proportion to their size, for fungal laccase as compared to that of plant laccase. Residues interacting with the model compounds at the respective enzyme active sites were found to be in conformity with their role in lignin biosynthesis and degradation. Molecular dynamics simulation analyses for the stability of docked complexes of plant and fungal laccases with lignin model compounds revealed that tetrameric lignin model compound remains attached to the active site of fungal laccase throughout the simulation period, while it protrudes outwards from the active site of plant laccase. Stability of these complexes was further analyzed on the basis of binding energy which revealed significantly higher stability of fungal laccase with tetrameric compound than that of plant. The overall data suggested a situation favorable for the degradation of lignin polymer by fungal laccase while its synthesis by plant laccase.

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