## 2 Characteristics of Lacases  
Metal-dependent lacase enzymes of the oxidoreductase class [EC 1.10.3.2] are included in the ligninolytic complex. Together with ascorbate oxidases, ceruoplasmin, bilirubin oxidase, phenoxazinone synthase and metallo-oxidase Fet3p, they belong to the multicopper oxidase (MCOs) family. These enzymes are characterized by their broad substrate specificity and in catalyzed reactions, they use molecular oxygen as an electron acceptor and produce a water molecule as a result of oxygen reduction. Oxidases of the MCO-type oxidize many polyphenic substrates and monomeric phenolic compounds, as well as diamines and metal ions [20]. The family of multicopper oxidases is related by the common structure of the catalytic center, in which at least four copper atoms are present. Based on the spectroscopic and magnetic properties of these copper atoms, they are classified as types T1, T2 and binuclear T3. The final product formation occurs through the oxidation of the substrate molecules to oxide radicals with the simultaneous reduction of an oxygen molecule to two water molecules according to the general notation: 4 RH + O\({}_{2}\)\(\rightarrow\) 4R\(-\) + 2H\({}_{2}\)O [21; 22; 23]. Lacases form multimetric complexes that can be mono-, di- or tetrameric glycoproteins. Each monomer has four copper atoms in its catalytic center: a type 1 (T1), type 2 (T2) and type 3 (T3). In the active center of MCOs, T2- and T3-type copper atoms occur close to one another, forming a trinuclear copper cluster (TNC). The T1-type mononuclear copper center occurs at a position approximately 12 A away from the others [24].  
The first of these, type T1, is the initial acceptor of electrons formed during the substrate oxidation reactions catalyzed by lacase, and the redox potential of the enzyme also depends on it. Typically in fungal lacases, this copper atom is bound to a histidine residue and one cysteine residue. Bacterial and plant lacases show a slightly different mechanism, in which the copper ion is coordinated to two histidines, one cysteine and an additional axial bond to one methionine, resulting in a tetrahedral geometry. In addition, TI gives the enzyme its blue color. A charge transfer from the cysteine residue to Cu (II) is responsible for the formation of the intense absorption band at 600 nm, which is associated with the blue color [24; 25].  
Based on the redox potential (E0) of the T1 copper center, we distinguish between lacases with low, medium and high redox potential. Low potential is characteristic of most lacases synthesized by bacteria and plants. Lacases with medium redox potential are typical of fungi of the genus _Myceliophthon_ or _Coprimosis_. In contrast, fungi of the genus _Tranetes_, belonging to the so-called white rot fungi, synthesize lacases with high redox potential [24; 25; 26; 27; 28]. Selected representatives of this group are shown in Figure 1.  
One of the essential functions of the T1-type copper center is to oxidize the substrate by taking up electrons and transferring them via the cysteine-histidine pathway to the NTC cluster. This mechanism results in the reduction of oxygen directly to water. The trinuclear cluster consists of binuclear type III copper atoms and mononuclear type II copper atoms. A Cu T2 atom with much lower light absorption is coordinated by two histidine molecules and one water molecule. Type III copper shows strong absorption at 330 nm as a result  
Figure 1: **(A)** Basidiomata of _Cerenua unicolor_, Poland. **(B)** Basidiomata of _Pleurotus ostreatus_ and the white rot wood, Poland. **(C)** Basidiomata of _Tranetes hirsuta_, Poland. **(D)** Basidiomata of _Tranetes trogit_, Poland. **(E)** Basidiomata of _Tranetes versicolor_, Poland. Photography by [PERSON].  
of charge transfer from the \(\mu\)-hydrox bridge (\(\mu\)-OH) to type III Cu (II). The T3 atom is coordinated by three histidine residues and one water molecule [24; 29; 30].