As Industrial Catalysts 2131 Advantages

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

Methyl syringate

3-Hydroxyanthranilic acid

1,2-Phenylenediamine

Benzene-1,2-dithiol

N-Hydroxyls/oxides/oximes

N-Hydroxybenzotriazole

N-Hydroxyacetanilide

Violuric acid

"N

oh I

"N

coch3

oh I

n coch3

o hn hn

N-Hydroxyphthalimide h

TEMPO

48 | 2 Catalytic Applications of Laccase Table 2.3 Continued

Phenoxazines, phenothiazines

Phenoxazine-10-propionic acid

Phenothiazine-10-propionic acid

Other redox-active organic compounds

ABTS

cooh ho3s

Redox-active metal complexes K4Fe(CN)6, Fe(CsHs)2, Fe(bipyridyl)3Cl2, K4Mo(CN)8, Mn(oxalate)

cooh

COOH

so3h o n

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