Light-Dependent Incorporation of Adenine Nucleotide into Noncatalytic Sites of Chloroplast ATP Synthase |
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Authors: | A N Malyan |
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Institution: | (1) Institute of Basic Biological Problems, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia |
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Abstract: | The binding of ADP and ATP to noncatalytic sites of dithiothreitol-modified chloroplast ATP synthase was studied. Selective binding of nucleotides to noncatalytic sites was provided by preliminary light incubation of thylakoid membranes with 14C]ADP followed by its dissociation from catalytic sites during dark ATP hydrolysis stimulated by bisulfite ions ("cold chase"). Incorporation of labeled nucleotides increased with increasing light intensity. Concentration-dependent equilibrium between free and bound nucleotides was achieved within 2-10 min with the following characteristic parameters: the maximal value of nucleotide incorporation was 1.5 nmol/mg of chlorophyll, and the dissociation constant was 1.5 microM. The dependence of nucleotide incorporation on Mg2+ concentration was slight and changed insignificantly upon substituting Ca2+ for Mg2+. Dissociation of nucleotide from noncatalytic sites was illumination-dependent. The dissociation kinetics suggested the existence of at least two nucleotide-binding sites with different dissociation rate constants. |
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Keywords: | ATP synthase CF0F1 noncatalytic sites chloroplasts |
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