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Abstract
Alkaline p-nitrophenylphosphate phosphatase (pNPPase) from the halophilic archaeobacterium Halobacterium salinarum (earlier halobium) was solubilised in reversed micelles of hexadecyltrimethylammoniumbromide (CTAB) in cyclohexane, with 1-butanol as co-surfactant. The hydrolysis of p-nitrophenylphosphate (pNPP) appeared to follow Michaelis-Menten kinetics. Km and Vmax depended on the method of reaction initiation. The kinetic parameters of halophilic pNPPase in CTAB reversed micelles with high salt concentration (0.85 M NaCl) were determined. pNPPase showed the same dependency on the buffer ionic strength in reversed micelles as in aqueous macrosolution. The dependence of the maximum reaction rate (Vmax) on the molar water/surfactant ratio (ω0 value) showed a bell-shaped curve for NaCl and KCl, with a maximum reaction rate being found at ω0 = 10.27. The pH value for the maximum reaction rate was 9.0. The optimum temperature for enzyme activity was around 45°C.