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

Abstract

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.

Nitrogen nutrition in the estuarine zone: the case of Suaeda maritima var. macrocarpa

“…2). Previous experiments have shown that variation of the sodium chloride concentration in the nutrient medium (0-390 mM) does not alter the affinity constants of the enzymes studied (Boucaud & Billard, 1978Billard, , 1981Billard & Boucaud, 1982). The K m values are similar to those of glyco- NO~.…”

“…The enzymes were extracted in 0.1 M phosphate buffer, pH = 7.5; Tris-HCl, pH = 8.1; tricine-KOH, pH = 7.6 and pH = 7.5, respectively, and desalted on a Sephadex G-25 column. They were further treated as described in Boucaud & Billard (1978, Billard & Boucaud (1980, 1982. Effects of the NaC1 concentration in the nutrient medium on enzyme activities were determined in root and shoot.…”

“…At optimal salinity, the halophytic nature is expressed by active protein synthesis with three salinity levels, viz. 0, 130, and 390 mM NaC1 (Boucaud & Billard, 1978). Both, nitrate (KNO3) and ammonium (NH4)2SO4, were present in a 8.3 mM and 4.2 mM concentration, respectively.…”

Glutamate dehydrogenase in the first leaf of wheat

“…A high specificity of soltible GDH in leaves for NAD was previously mentiotied (Ehmke andHartmann 1976, Barash et al 1976). On the contrary, GDH activities which were essentially NADP dependent were reported Thurman 1972, Boucaud andBillard 1978) when tightly bound enzymes, only released with detergents, were present.…”