The Chloride Sensitivity of Dunaliella parva Enzymes

Abstract

The NaCl resistance of enzymes in crude extracts from the extreme halotolerant alga Dunaliella parva was investigated. Enzymes exhibit a very broad scale of sensitivity against NaCl, ranging from half maximal inhibitions at 100 mM up to the molar range. Salt resistance depends on the type of the enzyme as well as on the substrate concentrations: Enzymes with nonelectrolytes exhibit a relatively higher salt tolerance than those with anionic substrates. Salt — inactivation is caused by Cl^- and not by K⁺ or Na⁺. A competitive type of interaction of the Cl^- anion with the anionic substrate is observed. Consequently high concentrations of anionic substrates protect enzymes in vivo against Cl^- inactivation.

Half maximal inhibition of enzymes from D. parva cells adapted to different salinities were not significantly different under substrate saturating conditions, but the KM-Values for the substrates increased with the salinity of the preculture.