Laccases (EC1.10.3.2) are copper-containing oxidaseenzymes that are found in many plants, fungi, and microorganisms. The copper is bound in several sites; Type 1, Type 2, and/or Type 3. The ensemble of types 2 and 3 copper is called a trinuclear cluster (see figure). Laccases act on phenols and similar molecules, performing a one-electron oxidations, which remain poorly defined. It is proposed that laccases play a role in the formation of lignin by promoting the oxidative coupling of lignols, a family of naturally occuring phenols.[1] Laccases can be polymeric, and the enzymatically active form can be a dimer or trimer.
The tricopper site found in many laccases, notice that each copper center is bound to imidazole (color code: copper is brown, nitrogen is blue).
The easiest way to detect activity in laccases is with a spectrophotometrically. Substrates that are commonly used with this method are ABTS, syringaldazine, 2,6-dimethoxyphenol, and dimethyl-p-phenylenediamine. Activity can also be monitored with an oxygen sensor as the oxidation of the substrate is paired with the reduction of oxygen to water.
Applications and potential utility
Laccases have been examined as cathode in an enzyme catalyzed fuel cell. They can be paired with an electron mediator to facilitate electron transfer to a solid electrode wire.
Laccase is one of the few oxidoreductases commercialized as industrial catalysts. The enzyme can be used for textile dyeing/finishing, wine cork making, and many other industrial, environmental, diagnostic, and synthetic uses (see, e.g., Feng Xu, (2005) Applications of oxidoreductases: Recent progress, Industrial Biotechnology 1, 38-50[1]).
References
^ Edward I. Solomon, Uma M. Sundaram, Timothy E. Machonkin "Multicopper Oxidases and Oxygenases" Chemical Reviews, 1996, Volume 96, pp. 2563-2606.
