Enzyme catalysis in water-organic solvent two-phase systems

As a milieu for enzyme reactions, the water-organic solvent two-phase system offers to broaden the applications of enzymes, particularly in the production of organic chemicals. In a two-phase system, an aqueous phase containing enzymes, cofactors and other water-soluble components is dispersed in an immiscible organic solvent containing hydrophobic substrates and products at high concentration. Two-approaches have been examined in this research: emulsification of an aqueous phase containing enzyme in an organic phase and the use of enzymes in a microencapsulated aqueous phase. Peroxidase, cholesterol oxidase and yeast alcohol dehydrogenase (YADH) are studied as model systems to determine experimentally the advantages, uses and limitations of these two approaches.;In an aqueous-organic dispersion, cholesterol oxidase exhibits Michaelis-Menten behavior in terms of substrate and enzyme concentrations, however the observed rate of reaction depends on the nature and concentration of surfactants added, agitation rate, and organic phase composition. Analysis of the experimental data in terms of simultaneous mass transfer with reaction indicates that the system may operate in the slow reaction-diffusional regime.;The peroxidase-catalyzed oxidation of p-anisidine with hydrogen peroxide exhibits different results in a two-phase dispersion and in an insoluble enzyme (low water) system. The reaction is very sensitive to the nature of the environment to which the enzyme is exposed. Reliable results could only be obtained in the two-phase dispersion.;Reaction kinetics limit cinnamyl alcohol oxidation catalyzed by YADH in a two-phase dispersion. Cofactor NAD;Microcapsules dispersed in organic solvents provide a suitable environment for conducting enzyme reactions involving cofactors and hydrophobic substrates. Encapsulated YADH is active and stable in cyclohexane provided the pH is adjusted appropriately. Mass transfer does not influence batch reaction rates. Conversion in a fluidized-bed reactor containing encapsulated YADH/NAD...