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1. Introduction
Species of Basidiomycetes are known to be very interesting fungi, including white rot fungi, which are considered the most promising group of microorganisms for degrading lignin due to extracellular enzyme production [1]. One of the most important ligninolytic enzymes is laccase (Lac, E.C. 1.10.3.2), which is a blue copper polyphenol oxidase containing four copper atoms per molecule in the catalytic centre and catalyses four electron reductions of oxygen to water [2]. Laccases are stable at an acidic pH and exhibit optimum activity within the pH range from three to six [3]. In addition, laccases are active over a wide range of temperatures (20-55 °C). Thermostable laccases (60-70 °C) were also purified and characterised [4]. It is not surprising that laccase production by Trametes, Pleurotus, Lentinula, Pycnoporus, Phanerochaete, and Agaricus has been widely studied [5].
It is known that production of various fungal laccases is controlled by different genes and that laccase exhibits different isoforms with a molecular weight within the range from 55 to 110 kDa [6]. The found laccase isoforms from various fungal strains are highly important because the different isoforms possess special catalytic properties [5] and provide new potential options for laccase application. However, utilisation of laccase isoforms in a wide variety of fields has been ignored due to the lack of commercial availability. Various applications of laccase in biotechnological areas have resulted in the need to expand the spectrum of laccase positive organisms and use their laccase-producing potential [7,8,9]. Because the industrial application of laccase is still hampered by a lack of long-term operational stability and the difficulty in recycling laccase, it is necessary to improve the properties of laccase, which could be partially solved by studying its various isoforms.
Enzyme immobilisation techniques are well recognised as a common way to overcome the aforementioned drawbacks. There are four principal methods for immobilization of enzymes, such as binding to a carrier by adsorption, entrapment or encapsulation in organic/inorganic polymer, covalent and cross-linking of proteins molecules [10]. Use of the carrier unavoidably leads to ‘dilution of activity’, owing to introduction of a large portion of non-catalytic ballast, which results in lower space-time yields and productivities. Furthermore, immobilization of the enzyme on the carrier often results in substantial loss of activity, especially at...