Effects of Salts on the Halophilic Alga Dunaliella viridis

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Abstract
Determinations of the salt sensitivity of enzymes extracted from the halophilic alga Dunaliella viridis revealed that pentose phosphate iso-merase, ribulose diphosphate carboxylase, glucose-6-phosphate dehydro-genase, and phosphohexose isomerase were inhibited by NaCl concentrations far lower than that in the growth medium (3.75 [image]). The inhibition was reversible and was not prevented by preparing the extracts in the presence of salt. K, Li, and Cs chlorides were equally inhibitory. In contrast, whole cells require rather high levels of NaCl for optimal growth, whereas growth is inhibited by low levels of the other cations. The results suggest a specific mechanism for the exclusion of sodium from the interior of the cell.