A general treatment for meaningful comparison of rate parameters of enzyme-catalyzed reactions in aqueous and reverse micellar solutions

A relevant question concerning the kinetics of reactions catalyzed by water-soluble enzymes in reverse micellar solutions is whether the efficiency of the enzyme is different from that in bulk aqueous solution. The comparison can be carried out only if the rates of the processes are compared under conditions of equal substrate activity. In the present work, it is proposed that this comparison can be carried out by employing the activity of the substrate in bulk water solution as a thermodynamic concentration scale. In order to carry out this comparison, the kinetic results obtained in the reverse micellar solution employing the analytical substrate concentration must be corrected by the solute distribution between the micellar pseudophase and the external solvent and by the partitioning of the substrate between the external solvent and an aqueous solution. The proposed methodology is applied to data previously reported for the oxidation of aliphatic alcohols catalyzed by alcohol dehydrogenase in a sodium 1,4-bis(2-ethylhexyl) sulfosuccinate/isooctane/water microemulsion. It is shown that when properly treated, the data indicate that the efficiency and selectivity of the enzyme is very similar in bulk aqueous solution and in the reverse microemulsion.