Enzymes Laccase modification

Kruus K., Niku-Paavola, M.L. and Viikari L.(2001) Laccase-a Useful Enzyme for Modification of Biopolymers, In Biorelated Polymers-Sustainable Polymer Science and Technology, E. Chiellini, H. Gil, G. Braunegg, J. Buchert, P. Gatenholm, and M. Van der Zee (eds.), Kluwer Academic/Plenum Publishers, pp.255-261... 

Polyphenol oxidase occurs within certain mammalian tissues as well as both lower (46,47) and higher (48-55) plants. In mammalian systems, the enzyme as tyrosinase (56) plays a significant role in melanin synthesis. The PPO complex of higher plants consists of a cresolase, a cate-cholase and a laccase. These copper metalloproteins catalyze the one and two electron oxidations of phenols to quinones at the expense of 02. Polyphenol oxidase also occurs in certain fungi where it is involved in the metabolism of certain tree-synthesized phenolic compounds that have been implicated in disease resistance, wound healing, and anti-nutrative modification of plant proteins to discourage herbivory (53,55). This protocol presents the Triton X-114-mediated solubilization of Vida faba chloroplast polyphenol oxidase as performed by Hutcheson and Buchanan (57). 

Gianfreda and Bollag (1994) investigated the behavior of laccase and peroxidase in the presence of a montmorillonite, a kaolinite, and a silt loam soil. They observed considerable variation in the retained activities of the two enzymes immobilized on the different supports as well as variation in the amount of each enzyme sorbed (Table 2.10). Interestingly enough, laccase immobilized on montmorillonite showed a higher specific activity (118%) than that of the free enzyme. This may be attributed to the steric modification of the immobilized enzyme or possibly due to the catalytic ability of montmorillonite itself. Their studies showed that the performance of these enzymes is significantly affected by soil mineral colloids. 

Witayakran, S., and Ragauskas, A.J. (2009) Modification of high-lignin softwood kraft pulp with laccase and amino acids. Enzyme Microb. Technol., 44 (3), 176-181. 

Liu N, Shi S, Gao Y, Qin M (2009) Fiber modification of kraft pulp with laccase in the presence of methyl syringate. Enzyme Microb Technol 44 89-95... 

With respect to the above requirements for DET, laccase and BOx have been shown to be useful bioelectrocatalysts for O2 reduction. For both en mes, the substrates to be oxidized or reduced interact at different locations within the enzyme structure thus it is possible to orientate these enzymes without physically blocking access for the second substrate. In addition to the above-mentioned orientation of BOx by carb-ojq late groups at the surface of electrodes, the modification of electrodes with phenolic-type heterocycles (such as anthracene, anthraquinone and naphthoquinone derivatives) has been shown to significantly enhance the orientation of both enzymes to the electrode surface via their T1 Gu center, resulting in increased bioelectrocatalytic O2 reduction at the TNG. ° The phenolic modifications of the electrode constructs mimic the natural substrates of the enzymes, which results in docking of the enzymes to the electrode surface at their T1 Gu center in BFGs, this electrode then acts as the biocathode of the device, utilizing O2 as the oxidant and final electron acceptor. 

The electrochemical insulation of the enzyme-active site by its protein or glycoprotein shell usually precludes the possibility of any direct electron-transfer with bulk electrodes [15]. However, under carefully controlled conditions, some enzymes can exhibit direct, nonmediated electrical communication with electrode supports, and biocatalytic transformations can be driven by these processes [16, 17]. For example, the direct electroreduction of O2 and H2O2 biocatalyzed by laccase [18] and horseradish peroxidase (HRP) [19], respectively, have been demonstrated. This unusually facile electronic contacting is believed to be the consequence of incompletely encapsulated redox centers. When these enzymes are properly orientated at the electrode surface, the electrodeactive site distance is short enough for the electron-transfer to proceed relatively unencumbered. Direct electron communication between enzyme-active sites and electrodes may also be facilitated by the nanoscale morphology of the electrode. The modification of electrodes with metal nanoparticles allows the tailoring of surfaces with features that can penetrate close enough to the enzyme active site to make direct electron-transfer possible [20, 21]. 

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