Abstract
Laccases are enzymes that have a great potential for use in breaking down toxic compounds. Fungal laccases show high enzymatic activity, especially those produced by basidiomycetes. Depending on the culture conditions and the strain used, a variety of isoenzymes and/or enzymatic activities can be obtained. In this study, extracellular laccase enzymes produced by Pleurotus ostreatus was identified in a submerged culture (SmF), with and without copper sulphate as a chemical inducer, and in a solid-state culture (SSF), using wheat straw as natural inducer. This study was conducted to observe the expression of the enzymes produced under the culture conditions tested and their persistence during the culture, as well as the extracellular activity produced and the correspondence that the isoenzymes presented between the intracellular and extracellular media. A positive effect of the inducers on the specific laccase activity was observed either in SmF with copper sulphate or SSF (41.11 and 40.43 UI/mg protein, respectively), compared with that obtained in SmF without copper sulphate (2.87 UI/mg protein). This effect was different only at the time when the highest activity appeared (360 and 120 h, respectively), showing advantages in SSF. The same three isoenzymes were observed in the three kinds of cultures. The main differences among the laccase profiles reside in the time when they appeared in each culture and only an additional form of lower molecular weight was observed in SSF. The laccase enzymes in the intracellular extracts were equal to those in the extracellular ones. The laccase isoenzymes profiles suggest that the presence of inducers helps in maintaining the activity through the culture time. Key words: Phenol oxidases, basidiomycete, enzymatic activity, copper, wheat straw, solid-state culture (SSF), submerged culture (SMF). 
Highlights
Pleurotus ostreatus is one of the most widely studied fungal species, because it is edible, has medicinal properties, and can produce enzymes used at experimental and industrial levels in food, medicine, andAfr
In the three conditions for growing this P. ostreatus strain, three bands corresponding to isoenzymes were observed with laccase activity over dimethoxy phenol (DMP)
In the SmF, with and without copper sulphate, the enzymatic activities obtained depicted the same behavior reported by others authors in previous papers (DSouza et al, 1999; Palmieri et al, 2000) where the influence of Cu as the inducer increased the activity around 20 times
Summary
Pleurotus ostreatus is one of the most widely studied fungal species, because it is edible, has medicinal properties, and can produce enzymes used at experimental and industrial levels in food, medicine, andAfr. Laccases (benzenediol: oxygen oxide-reductases EC 1.10.3.2) are glycoproteins known as blue multi copper oxidases They are monomeric enzymes, some of them are multimeric, intracellular or extracellular, and belong to the family of phenoloxydases, which act on ρ-diphenols (Palmieri et al, 2000). They have a catalytic site, characterized by four copper atoms linked to three REDOX sites (T1, T2, and T3), through which it binds to four electrons to reduce oxygen to water, while oxidizing a wide spectrum of substrates (Kunamneni et al, 2008). The nomenclature established by the IUPAC-IUB (1981) recommends to restrict the use of the term "isoenzyme" to enzymatic products with the same catalytic activity but different due to genetic causes
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