Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Bioremediation: An effective approach of mercury removal from the aqueous solutions

Mercury (Hg(II)) is the 16th rarest element present in the earth's crust. Due to rapid industrialization and urban expansions, the mercury concentration has been elevated in the environment. Hg(II) contamination in the aqueous environment has become a great challenge for human beings. The main source of Hg(II) in the aqueous phase is untreated effluent industries (such as the paper industry). Hg(II) is non-biodegradable in nature and even its trace amount in an aqueous environment can pose chronic threats among the humans (damage to the central nervous system, respiratory system, and cardiovascular system, mutation of DNA), animals, and aquatic creatures. Therefore, the removal of mercury from aqueous solutions is an urgent need of the modern era. The conventional techniques such as ion exchange, precipitation, membrane filtrations are costly and also generate byproducts in the environment. Bioremediation is a sustainable, environmentally sound, and cost-effective technique to remove Hg(II) from the aqueous solutions. In this process, naturally occurring microorganisms are utilized to remove the Hg(II) from the aqueous solutions. Lentinus edodes, U. lactuca, and Typha domingensis are found to have great potential to remove mercury from water ranged from ~100 mg g^-1 to 337 mg g^-1.

Inhibition in multicopper oxidases: a critical review

This review critiques the literature on inhibition of O₂-reduction catalysis in multicopper oxidases like laccase and bilirubin oxidase and provide recommendations for best practice when carrying out experiments and interpreting published data.

A first report on competitive inhibition of laccase enzyme by lignin degradation intermediates

Laccases have been widely explored for their ligninolytic capability in bioethanol production and bioremediation of industrial effluents. However, low reaction rates have posed a major challenge to commercialization of such processes. This study reports the first evidence of laccase inhibition by two types of lignin degradation intermediates - fungal-solubilized lignin and alkali-treated lignin - thus offering a highly plausible explanation for low reaction rates due to buildup of inhibitors during the actual process. Reversed-phase high-performance liquid chromatography revealed the presence of similar polar compounds in both lignin samples. A detailed kinetic study on laccase, using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as the substrate, was used to calculate the Michaelis constant (K_m) and maximum reaction rate (V_max). With an increase in the concentration of lignin degradation intermediates, V_max remained nearly constant, while K_m increased from 1.3 to 4.0 times that of pure laccase, revealing that the inhibition was competitive in nature. The kinetic studies reported here and the insight gained into the nature of inhibition can help design process strategies to mitigate this effect and improve overall process efficiency. This work is applicable to processes that employ laccase for delignification of biomass, such as second-generation biofuels processes, as well as for industrial effluent treatment in paper and pulp industries.