Kinetic regulation of an alkaline p-nitrophenylphosphate phosphatase from Halobacterium salinarum in low water system by Mn2+ and monovalent cations

Reversed micelles were used as a cytoplasmic model to study the effect of t he multi-ionic equilibria on kinetics of extreme halophilic enzymes. The en zymatic system used was an alkaline p-nitrophenylphosphate phosphatase from the halophilic archaeon Halobacterium salinarum (earlier halobium). This e nzyme was solubilised in reversed micelles of hexadecyltrimethylammonium br omide in cyclohexane, with l-butanol as co-surfactant. The p-nitrophenylpho sphate phosphatase is a good system to study the regulation of the enzymati c activity, because it utilises manganese, water and potassium or sodium as cofactors and reacts with p-nitrophenylphosphate. Kinetic behaviour was de termined by the ratio between [Mn2+] and [Na+] or [K-]. When the [Mn2+] inc reased and [Na+] or [K+] decreased, the kinetics showed cooperative behavio ur. Rabin`s model describes the kinetic behaviour of the p-nitrophenylphosp hate phosphatase in reversed micelles. (C) 2001 Federation of European Micr obiological Societies. Published by Elsevier Science B.V. All rights reserv ed.