Ligninolytic activity

Since many years, pectolytic enzymes have been widely used in industrial beverage processing to improve either the quality and the yields in fruit juice extraction or the characteristics of the final product [1,2]. To this purpose, complex enzymatic mixtures, containing several pectolytic enzymes and often also cellulose, hemicellulose and ligninolytic activities, are usually employed in the free form. The interactions among enzymes, substrates and other components of fruit juice make the system very difficult to be investigated and only few publications are devoted to the study of enzymatic pools [3-5], An effective alternative way to carry out the depectinisation process is represented by the use of immobilized enzymes. This approach allows for a facile and efficient enzymatic reaction control to be achieved. In fact, it is possible to avoid or at least to reduce the level of extraneous substances originating from the raw pectinases in the final product. In addition, continuous processes can be set up. 

Extracellular peroxidases are produced by Streptomyces chromofuscus, with the capability to decolorize azo dyes associated to ligninolytic activity in aerobiosis. Azo dyes are converted to cationic radicals, which are subjected to nucleophilic attack by water or hydrogen peroxide molecules, producing reactive compounds that undergo redox reactions that result in a more stable intermediate [37]. 

In Phanerochaete flavido-alba, an induction of ligninolytic activities that was ascribed to phenolic compounds was evidenced [69]. Phenols have also been shown to have an important role as redox mediators for dye degradation with laccases from Pycnoporus cinnabarinus and Trametes villosa, and they resulted to be necessary to degrade a strongly recalcitrant azo dye, the Reactive Black 5 [70]. 

The level of cyclic AMP (cAMP) is increased by nitrogen starvation this triggers expression of ligninolytic activity and veratryl alcohol biosynthesis (40). 

However, there are two articles which report evidence against these relationships between biosynthesis of this secondary metabolite and lignin decomposition (43,44). For example, a mutant of P. chrysosporium, which does not produce veratryl alcohol, has ligninolytic activity (43). Another mutant, which lacks glucose oxidase, is unable to decompose lignin to CO2 and therefore is ligninase Mess. It is, however, able to produce about 30% of the amount of veratryl alcohol normally found in the fungus (44). 

Figure 1. Time course of of ligninolytic activity (conversion of ring-labelled 14C-DHP to 14C02), biomass concentration, VAO activity and laccase activity during growth of Pleuroius sajor-caju in agitated mycological broth cultures. (Reproduced with permission from Ref. 25, 1988, Biochemical Society).

Agitation of P. chrysosporium cultures was originally found to strongly suppress ligninolytic activity -lignin —> and it was reported that LiP activity was... 

P Fenn, S Choi, TK Kirk. Ligninolytic activity of Phanerochaete chrysosporium physiology of suppression by NHf and L-glutamate. Arch Microbiol 130 66-71, 1981. 

P Fenn, TK Kirk. Relationship of nitrogen to the onset and suppression of ligninolytic activity and secondary metabolism in Phanerochaete chrysosporium. Arch Microbiol 130 59-65,1981. 

Since ligninolytic activity was required for extensive mineralization of TNT, the accumulation of substrates of the ligninolytic enzymes originating from aminodinitrotoluenes was expected under non-ligninolytic conditions. Nitrogen-sufficient (12 mM ammonium tartrate) agitated cultures were incubated with 4-amino-2,6-dini-trotoluene for 48 h, and a transformation product was extracted, purified by preparative thin layer chromatography and analyzed by mass spectroscopy. By comparison with chemically synthesized reference compounds it was identified as 4-formamido-2,6-dinitrotoluene. 

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