Caractérisation de la glutamate déshydrogénase chez un halophyte obligatoire: le Suaeda maritima var. macrocarpa

Characterization of the glutamate dehydrogenase from an obligate halophyte: Suaeda maritima var. macrocarpa The glutamate dehydrogenase (GDH), E.C. 1.4.1.3, of the obligate halophyte Suaeda maritima (L.) Dum. var. macrocarpa Moq. has been studied. NaCl increase in the culturing solution (0 to 23 g NaCl/litre) lowers the specific activity but does not affect the kinetic characteristics of the enzyme collected after purification on G-25 Sephadex gel. In optimal conditions, GDH is activated by the addition of 25 mM NaCl in the incubation medium and inhibited with concentrations over 100 mM. The inhibitory activity of the salt induces both a modification of the affinity of the enzyme for substrate (competitive inhibition for ketoglutarate) and a modification of the catalytic potency (non-competitive inhibition with NADH and ammonium ion). It is suggested that NaCl has a depressing influence on GDH synthesis. There is a fundamental difference between its short time action (in vitro) versus its continuous effect in the culturing solution.