Affiliation:
1. Instituto de Bioquı́mica Vegetal y Fotosı́ntesis, Centro de Investigaciones Isla de la Cartuja, Universidad de Sevilla-Consejo Superior de Investigaciones Cientı́ficas, Avenida Américo Vespucio s/n, 41092-Sevilla, Spain
Abstract
Abstract
NAD-isocitrate dehydrogenase (NAD-IDH) from the eukaryotic microalgaChlamydomonas reinhardtii was purified to electrophoretic homogeneity by successive chromatography steps on Phenyl-Sepharose, Blue-Sepharose, diethylaminoethyl-Sephacel, and Sephacryl S-300 (all Pharmacia Biotech). The 320-kD enzyme was found to be an octamer composed of 45-kD subunits. The presence of isocitrate plus Mn2+ protected the enzyme against thermal inactivation or inhibition by specific reagents for arginine or lysine. NADH was a competitive inhibitor (Ki, 0.14 mm) and NADPH was a noncompetitive inhibitor (Ki, 0.42 mm) with respect to NAD+. Citrate and adenine nucleotides at concentrations less than 1 mm had no effect on the activity, but 10 mm citrate, ATP, or ADP had an inhibitory effect. In addition, NAD-IDH was inhibited by inorganic monovalent anions, butl-amino acids and intermediates of glycolysis and the tricarboxylic acid cycle had no significant effect. These data support the idea that NAD-IDH from photosynthetic organisms may be a key regulatory enzyme within the tricarboxylic acid cycle.
Publisher
Oxford University Press (OUP)
Subject
Plant Science,Genetics,Physiology
Cited by
17 articles.
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