Light-dependent incorporation of adenine nucleotide into noncatalytic sites of chloroplast ATP synthase.
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.
Malyan
A N
AN
Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia. Malyan@issp.serpukhov.su
D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020134:Catalytic Domain; D002736:Chloroplasts / Q000201:enzymology*; D006868:Hydrolysis; D008027:Light; D006180:Proton-Translocating ATPases / Q000378:metabolism*
D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases