Some Properties of Glutamate Dehydrogenase from the Marine Red Alga Gracilaria sordida (Harv.) W. Nelson
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Glutamate dehydrogenases (GDH, EC 126.96.36.199-4) catalyse the entry of ammonium into the organic cycle via amination of a-ketoglutarate and its release via deamination of Lglutamate. NAD-GDH facilitates NAD-/NADP-dependent deamination while NADPH-GDH facilitates NADH-/NADPH-dependent amination reactions. In the study reported here, GDHs were extracted from the red alga Gracilaria sordida and purified 10- to 180-fold before examining their amination and deamination reaction properties. NAD-/NADP- and NADH-/ NADPH-dependent activities were the order of 11:1 and 1:1.8, respectively. The pH optima for amination and deamination were 8.2 and 8.4 under NADH- and NADPH- and 8.4 and 9 under NAD- and NADP- dependent activities, respectively. Whereas both NAD- and NADP-dependent deamination activities were activated by calcium ions (Ca2+), only NADPH-dependent amination was activated. The Km values (in mM) were 3.0–3.6 for ammonia, 2.0–3.3 for a-ketoglutarate, 0.00286 for NADH, 0.0033 for .....