Mechanism of adaptation of an atypical alkaline p ‐nitrophenyl phosphatase from the archaeon Halobacterium salinarum at low‐water environments

Enzymes suspended in organic solvents represent a versatile system for studying the involvement of water in catalytic properties and their flexibility in adapting to different environmental conditions. The extremely halophilic alkaline p ‐nitrophenylphosphate phosphatase from the archaeon Halobacterium salinarum was solubilized in an organic medium consisting of reversed micelles of hexadecyltrimethylammoniumbromide in cyclohexane, with 1‐butanol as cosurfactant. Hydrolysis of p ‐nitrophenylphosphate was nonlinear with time when the enzyme was microinjected into reversed micelles that contained substrate. These data are consistent with a kinetic model in which the enzyme is irreversibly converted from an initial form to a final stable form during the first seconds of the encapsulation process. The model features a rate constant ( k ) for that transition and separate hydrolysis rates, v 1 and v 2 , for the two forms of the enzyme. The enzyme conversion may be governed by the encapsulation process. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 78: 497–502, 2002.