Catalysis by Laccase (From Coriolus uersicolor) in Microheterogeneous Media of the Water/Organic Solvent/Surfactant Type

Abstract

Catalysis by laccase from Coriolus uersicolor solubilized in the ternary systems of surfactant/water/organic solvent type, namely, Aerosol OT/water/octane, Brij 56/water/cyclohexane and egg lecithin/water/octane + pentanol + methanol mixture, has been studied. The laccase activity is found to depend, in principle, not only on the water/surfactant molar ratio, but on the surfactant concentration (with its hydration degree being constant) as well. The following inferences should be emphasized. Firstly, in all the systems under study, the catalytic activity (k_cat) of laccase entrapped into surfactant reversed micelles increases more than 50 times (when the surfactant concentration is extrapolated to zero) compared with the k_cat value in aqueous solution. Secondly, the catalytic activity (k_cat) of laccase entrapped in hydrated Aerosol OT aggregates, having lamellar, reversed cylindrical (hexagonal) and reversed micellar structure, depends greatly on the aggregate type. In other words, the phase transitions, i.e. an alteration in the packing of hydrated Aerosol OT molecules, evokes a sharp reversible change in the enzymatic activity. Thirdly, in the same phase, the catalytic activity of the solubilized enzyme depends on the linear dimensions of water cavities inside the surfactant aggregates (i.e. on the water content in the system under study). All these effects, regulating enzymatic activity, are probably caused by an alteration of the conformational mobility of laccase molecules incorporated into the inner polar cavities inside the surfactant aggregates.

Key Words:

• Micellar enzymology
• membranology
• superactivity of enzymes
• enzymatic activity regulation
• microheterogeneous organic media for enzymatic reactions