© 2002 Heron Publishing—Victoria, Canada
Reverse micelles in organic solvents: a medium for the biotechnological use of extreme halophilic enzymes at low salt concentration
Frutos C. Marhuenda-Egea (1, 2), Sonsoles Piera-Velázquez (1, 3), Chiquinquirá Cadenas (1) and Eduardo Cadenas (1)
1. División de Bioquímica, Facultad de Ciencias, Universidad de Alicante, Apartado 99, 03080 Alicante, Spain / 2. Author to whom correspondence should be addressed ([email protected]) / 3. Thomas Jefferson University, BLSB 511, 233 South 10th Street, Philadelphia PA 19107, USA / Received December 19, 2001; accepted March 8, 2002; published online April 10, 2002
Alkaline p-nitrophenylphosphate phosphatase (pNPPase) from the halophilic archaeobacterium Halobacterium salinarum (previously halobium) was solubilized at low salt concentration in reverse micelles of hexadecyltrimethylammoniumbromide in cyclohexane with 1-butanol as cosurfactant. The enzyme maintained its catalytic properties under these conditions. The thermodynamic “solvation–stabilization hypothesis” has been used to explain the bell-shaped dependence of pNPPase activity on the water content of reverse micelles, in terms of protein–solvent interactions. According to this model, the stability of the folded protein depends on a network of hydrated ions associated with acidic residues at the protein surface. At low salt concentration and low water content (the ratio of water concentration to surfactant concentration; w0), the network of hydrated ions within the reverse micelles may involve the cationic heads of the surfactant. The bell-shaped profile of the relationship between enzyme activity and w0 varied depending on the concentrations of NaCl and Mn2+.
Keywords: alkaline phosphatase, archaea, CTAB, Halobacterium.
ISSN 1472-3654 (Online) ISSN 1472-3646 (Print) Copyright © 2002–2007 Heron Publishing