Optimum pH for laccase exhibited variation which may be due to changes in the reaction caused by the substrate (syringaldazine), oxygen or the enzyme itself. The highest activity of the

produced GS-7340 datasheet laccase was at pH 5 with syringaldazine as a substrate in agreement with the previous work [41]. Relative high thermostability is an attractive and desirable characteristic of an enzyme. In general, the optimum temperature for laccase activities can differ from one strain to another, with a range for most fungal laccases being 50–70 °C [42], in our case, laccase had optimum temperature at 30–50 °C and rapidly lost activity at temperatures above 60 °C which might be due to breaking down the integrity of laccase protein structure and so losing much of its activity [43] and [44]. In general, laccase responds similarly to several inhibitors of enzyme activity. Many ions such as azide and halides can bind to the type 2 and type 3 copper atoms, resulting in the interruption of internal electron transfer with the subsequent inhibition of activity [45]. EDTA did not inhibit laccase activity as was observed with the laccase obtained from an unidentified basidiomycete [46]. Some of the most toxic dyes are amino-substituted azo dyes, which are often mutagenic and carcinogenic. Current methods for dye-decolorization are chemically derived and include adsorption,

chemical transformation, and incineration [47]. It has been suggested that enhanced microbial decolorization of dyes may provide a less Alpelisib cost expensive and more environmentally acceptable alternative to chemical treatment. An advantage of using fungal oxidative mechanisms to degrade azo dyes over other microorganisms is that it is possible to avoid the formation of hazardous breakdown Farnesyltransferase products such as anilines formed by the reductive cleavage of azo dyes [48]. The laccase oxidative transformation of dyes depends on their chemical structure.

The presence of ortho-hydroxy groups with respect to the azo link was found to enhance the decolorization rates of azo-dyes with laccase whereas nitro groups stabilized the dye molecules against laccase action [49]. Green synthesis of nanoparticles using microorganisms or enzymes provides advancement over chemical and physical method as it is cost effective, environment friendly, easily scaled up for large scale synthesis and in this method there is no need to use high pressure, energy, temperature and toxic chemicals [50]. Studies have shown that the secreted proteins/enzymes and reducing agents such as amino acids, peptides and organic acids in biological entities, are found to be responsible for nanoparticle production. Similarly, in this study, laccase from Pleurotus ostreatus served as a rich source for the proteins and free amino groups reducing gold into GNPs.