title: The influence of structure and composition of a reverse SDS microemulsion on enzymatic activities and electrical conductivities.
abstract: The activity of the enzyme horse radish peroxidase (HRP) is studied in a series of reverse microemulsions composed of dodecane, aqueous buffer, sodium dodecylsufate (SDS) and alcohols of the homologous series 1-butanol to 1-octanol. The HRP catalyzed reaction is the oxidation of a classical water soluble substrate, the 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) by hydrogen peroxide. In parallel electrical conductivity measurements are performed on the same solutions. The structural changes in the microemulsions, as inferred by the conductivity measurements, correlate remarkably well with the changes in the enzymatic activities. In particular it is found that (a) the maximum activity of the enzyme is always related to its optimum hydration and that this hydration can be related to the microemulsion structures, (b) the enzyme inhibition caused by the alcohols in microemulsions is a consequence of both the solubility of the alcohols in the buffer and the rigidity of the interfacial film. Consequently, it can be concluded that enzymatic activity measurements are a valuable tool to study confined systems such as microemulsions and, in particular, the amount of available hydration water. Enzymatic activities can be finely tuned by small changes in microemulsion structures, probably in a predictive way.
authors: Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany.
authors: Pierre
authors: P
authors: Bauduin
authors: Didier
authors: D
authors: Touraud
authors: Werner
authors: W
authors: Kunz
authors: Marie-Pierre
authors: MP
authors: Savelli
authors: Sylviane
authors: S
authors: Pulvin
authors: Barry W
authors: BW
authors: Ninham
mesh_terms: D000438:Alcohols / Q000737:chemistry; D000473:Alkanes / Q000737:chemistry; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004553:Electric Conductivity; D004655:Emulsions / Q000737:chemistry; D004789:Enzyme Activation; D006735:Horseradish Peroxidase / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000438:Alcohols; D000473:Alkanes; D004655:Emulsions; D014867:Water; C007548:n-dodecane; D012967:Sodium Dodecyl Sulfate; D006735:Horseradish Peroxidase