Enzymatic activity of an extremely halophilic phosphatase from the Archaea Halobacterium salinarum in reversed micelles

Alkaline p-nitrophenylphosphate phosphatase (pNPPase) from the halophilic archaeon Halobacterium salinarium (previously halobium) was solubilized in reversed micelles of cetyltrimethylammonium bromide (CTAB) in cyclohexane with 1-butanol as cosurfactant. The hydrolysis reaction appears to follow Michaelis-Menten kinetics. The dependency of the maximum reaction rate (V-max) on the water content theta (% v/v) (or omega(0) value: molar ratio of water to surfactant concentrations) showed a bell-shaped curve for 0.3 M CTAB, but not for 0.2 M CTAB. The enzyme activity increased with the surfactant concentration at a constant omega(0) value(10.27). When the surfactant concentration was increased at a constant theta, the enzyme activity decreased. The enzyme was more stable in reversed micelles than in aqueous media. (C) 2000 Elsevier Science B.V. All rights reserved.