5
). Therefore, knowledge of the composition and structure Enzymes entrapped in systems formed with water, phospholipof reverse micelles is necessary for the design of systems in ids, toluene, and Triton X-100 show a catalytic activity that is which stability and/or catalytic activity can be optimized. much lower and a thermostability that is much higher than that It has been reported, that increasing amounts of water inobserved in totally aqueous systems or in other types of reverse crease the water core of reverse micelles (6). The rate of micelles. By phase boundary titrations and dynamic light scattercatalysis of enzymes entrapped in reverse micelles increases ing, this work characterizes reverse micelle systems formed in as the size of the water pool is increased. At optimal water either toluene or propylbenzene with Triton X-100 and water. Four concentrations activity may reach the values observed in regions with distinct structural features were encountered. Up to 100% aqueous systems (7-10). In systems formed with one molecule of water per one Triton X-100 molecule, the system was transparent; light scattering measurements of this region indi-phospholipids, toluene, and water (11,12), or those which cated that water hydrated Triton X-100 monomers. A turbid region in addition contain Triton X-100 (13), the same general was formed as water content was increased to water:Triton X-100 phenomena were observed; however, in these systems enratios of 7.6 in toluene and 4.2 in propylbenzene. This thermodyzymes exhibit a catalytic activity that is much lower and a namically unstable region was formed by large polydisperse structhermostability that is much higher than that observed in tures. Transparent systems containing small size (27-150 A ˚) thertotally aqueous systems or in other types of reverse micelles modynamically stable reverse micelles were formed when the ratio (12)(13)(14). This system has been also used to study enzyme of water to Triton X-100 molecules in the reverse micelle was in activation by denaturants (15) and the relation between enthe range of 7.6 to 26.8 in toluene and 4.2 to 15.1 in propylbenzene.
zyme catalysis and molecular wear and tear (16). In spite
In this region, micellar size increased with water content. Water of the information obtained about protein function in the concentrations higher than the latter values resulted in phase sepatoluene/Triton X-100/phospholipids/water system, little is ration. A similar titration of the aforementioned systems in the presence of phospholipids revealed that in the first region of trans-known about the phase behavior and structural properties of parency up to 10 molecules of water hydrated a phospholipid this system. Because knowledge of the structural properties molecule. The inclusion of phospholipids to the Triton X-100 sysof the reverse micelles that affect enzyme activity and stabiltems caused a displacement of the boundaries of the second region ity is of importance for basic and practical reasons (3, 5, of transparency toward higher water contents. ᭧ 1998 Academic Press 17), we have characterized by phase boundary titrations and Key Words: reverse micelles; nonionic surfactants; Triton X-100; dynamic light scattering (DLS) the systems formed when enzymes.
low amounts of water are added to Triton X-100 with or without phospholipids in two organic solvents of different polarity.