The dependence of a halophilic malate dehydrogenase on ωo and surfactant concentration in reverse micelles

Abstract

The halophilic malate dehydrogenase (hMDH) activity of Halobacterium salinarum was studied as a function of micelle size ( ω o), in cethyltrimethylammonium bromide (CTAB)/cyclohexane reverse micelles, with 1-butanol as cosurfactant. The velocity dependence of the ω o profile depends on the buffer used, the surfactant concentration, and the salt concentration. In phosphate buffer, the activity increases with increasing water content, while in Tris/HCl buffer a bell-shaped profile is generally observed. Despite a slight change in the ω o-activity profile, the enzymatic activity was higher at low salt concentration even when we employed a different buffer. The ω o value for the maximal activity (optimum ω o) varies directly with the enzyme concentration. The hMDH activity in reverse micelles depends on the surfactant concentration and the dependence of the activity of this enzyme on the surfactant concentration, at constant ω o, is different for each ω o value.