Effect of Methanol on the Nucleotide Binding to High-Affinity Sites on Chloroplast Coupling Factor 1

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The effects of methanol on the nucleotide binding to isolated chloroplast coupling factor 1 (CF_1) were investigated. Isolated CF_1 has four kinds of nucleotide binding sites; a barely dissociable ADP-binding site (site A), two slowly exchangeable high-affinity sites with different affinities for ADP (sites B and C) which are not catalytic sites, and several low-affinity sites (Hisabori and Sakurai 1984). Methanol at 20% (v/v) slightly accelerated the binding of ADP to CF_1, but did not influence the number of binding sites. Methanol at 10-24% (v/v) affected neither the total amounts of bound adenine nucleotides (~2.5 mol/mol CF_1) nor the incorporation of labeled ADP from the medium (~1.5 mol/mol CF_1) into the slowly exchangeable sites (sites A, B, C). These results indicate that no appreciable exchange of ADP occurred at site A at 10-24% (v/v) methanol and exclude the possibility of direct participation of nucleotide binding at this site in the regulation of ATPase. In 32% methanol, the amount of the labeled ADP bound increased, suggesting some exchange at site A. Methanol at 20% (v/v) greatly increased the affinities of sites B and C for ADP, CDP, GDP, UDP and PP_i. Conformational change of CF_1 Induced by the binding of nucleotides to site(s) B (and C) increased the resistance of CF_1 to inactivation by methanol at high concentrations or by cold treatment.
日本植物生理学会の論文