Phospholipid reverse micelles as a milieu of an enzyme reaction in an apolar system

Alkaline phosphatase was entrapped in reverse micelles formed in n-heptane with surfactants (bis(2-ethylhexyl)sodium sulfosuccinate, phosphatidylcholine, phosphatidylethanolamine, or phosphatidic acid) and water. The entrapped enzyme could express its activity in the reverse micelles of the above surfactants only when the substrate, p-nitrophenylphosphate, was within the reverse micelles of bis(2-ethylhexyl)sodium sulfosuccinate. The optimum pH of activity in the reverse micelles was higher by about one pH unit than that determined in bulk water. Regardless of water content (mol water/mol surfactant = 10 or 14.8), the Km value was about 30 mM, while Vmax at the higher water content (14.8) was 2-4 times greater than that at 10. Activation energy of the reaction depended on the kind of reverse micelles. Differences in carbon chain length of solvents showed no effect on the kinetic properties of the enzyme.