Like many applied enzymes, a laccase catalyst should operate under ambient conditions, thereby save energy, and is biodegradable. Compared with peroxidases and other oxidoreductases, laccases may potentially have additional advantages as industrial catalysts:
1. Laccases use readily available, inexpensive, and safe O2 as co-substrate.
2. Laccases can oxidize a wide range of molecules (as their reducing substrates). These include phenols, anilines, thiols, N-hydroxyls, N-oxides, N-oximes, phenazines, phenoxazines, phenothiazines, transition metal complexes, and so forth (Table 2.3). Many of the compounds occur naturally and/or can be important industrial precursors, products, or byproducts. Their transformability by laccases might allow various viable applications of these enzymes.
3. Laccases can be produced industrially by fermentation. Many fungal laccases can be secreted by hosts engineered to remove undesirable contaminants and/or toxins, making their recovery and formulation relatively straightforward. Peroxidases and some other oxidoreductases often require complex cofactors (for example, heme and flavin), whose biosynthesis may severely limit the overall expression of the holoenzyme. Supplementing these cofactors exogenously could be prohibitively expensive. In contrast, laccase employs Cu as cofactor, which can be readily supplied by simple, inexpensive Cu salts.
2.1 Properties of Classical Laccase | 47 Table 2.3 Types and examples of molecules directly oxidizable by laccases.
Phenols, anilines, benzenethiols
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48 | 2 Catalytic Applications of Laccase Table 2.3 Continued
Other redox-active organic compounds
Redox-active metal complexes K4Fe(CN)6, Fe(CsHs)2, Fe(bipyridyl)3Cl2, K4Mo(CN)8, Mn(oxalate)
so3h o n
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