Interactions between magnesium ions,pH, glucose-6-phosphate,and NADPH/NADP+ ratios in the modulation of chloroplast glucose-6-phosphate dehydrogenase in vitro |
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Authors: | K. J. Lendzian |
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Affiliation: | (1) Institut für Botanik und Mikrobiologie, Lehrstuhl für Botanik, Technische Universität, Arcisstr. 21, D-8000 München 2, Federal Republic of Germany |
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Abstract: | Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) from spinach chloroplasts is strongly affected by interactions between Mg2+, proton, and substrate concentrations. Mg2+ activates the enzyme to different degrees; however, it is not essential for enzyme activity. The Mg2+-dependent activation follows a maximum curve, magnitude and position of the maximum being dependent on pH and NADPH/NADP+ ratios. At a ratio of zero and pH 7.2, maximum activity is observed at 10 mM Mg2+. Increasing the NADPH/NADP+ ratio up to 1.7 (a ratio measured in the stroma during a light period), maximum activity is shifted to much lower Mg2+ concentrations. At pH 8.2 (corresponding to the pH of the stroma in the light) and at a high NADPH/NADP+ ratio, enzyme activity is not affected by the Mg2+ ion. The results are discussed in relation to dark-light-dark regulation of the oxidative pentose phosphate cycle in spinach chloroplasts.Abbreviations DTT dithiothreitol - G-6-P glucose-6-phosphate - G-6-PDH glucose-6-phosphate dehydrogenase (EC 1.1.1.49) - PPC pentose phosphate cycle |
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Keywords: | Chloroplasts Glucose-6-phosphate dehydrogenase Magnesium ions NADPH/NADP+ ratio pH-regulation Spinacia |
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