title: An extreme halophilic enzyme active at low salt in reversed micelles.
abstract: Possible biotechnological applications of extreme halophilic enzymes are strongly determined by their high salt requirement of around 4 M NaCl. Consequently, the use of these in organic media seemed to be unlikely. However, we have succeeded in dissolving a halophilic enzyme, p-nitrophenylphosphate phosphatase from the archaeon Halobacterium salinarum, in an organic medium by creating a reverse micellar system with very low salt concentration. The enzyme retained its catalytic properties in reversed micelles made with an anionic surfactant (dioctyl sodium sulphosuccinate) or with a cationic surfactant (hexadecyltrimethylammonium bromide) in cyclohexane plus 1-butanol as co-surfactant. The dependence of the rate of hydrolysis of p-nitrophenylphosphate phosphate on the molar water/surfactant ratio (w(0) value) showed a bell-shaped curve for each surfactant system. Kinetic parameters were determined in each system. The enzymatic reaction appeared to follow Michaelis-Menten kinetics with the anionic surfactant only. The kinetic behaviour was determined at different concentrations of Mn(2+) in reversed micelles of dioctyl sodium sulphosuccinate as surfactant.
authors.affiliation: División de Bioquímica, Facultad de Ciencias, Universidad de Alicante, Apt. 99, 03080 Alicante, Spain. frutos@ua.es
authors.forename: Frutos C
authors.initials: FC
authors.lastname: Marhuenda-Egea
authors.forename: Sonsoles
authors.initials: S
authors.lastname: Piera-Velázquez
authors.forename: Chiquinquirá
authors.initials: C
authors.lastname: Cadenas
authors.forename: Eduardo
authors.initials: E
authors.lastname: Cadenas
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000737:chemistry / Q000378:metabolism*; D000838:Anions; D002384:Catalysis; D002412:Cations; D000077286:Cetrimonium; D002593:Cetrimonium Compounds; D004143:Dioctyl Sulfosuccinic Acid; D004795:Enzyme Stability; D019617:Halobacterium salinarum / Q000201:enzymology*; D006868:Hydrolysis; D007700:Kinetics; D008345:Manganese / Q000494:pharmacology; D008823:Micelles; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000494:pharmacology; D013501:Surface-Active Agents
chemical_list: D000838:Anions; D002412:Cations; D002593:Cetrimonium Compounds; D008823:Micelles; D013501:Surface-Active Agents; D004143:Dioctyl Sulfosuccinic Acid; D008345:Manganese; D012965:Sodium Chloride; D009597:4-Nitrophenylphosphatase; D000077286:Cetrimonium