Energy-dependent changes in the conformation of the chloroplast ATP synthase and its catalytic activity

Chloroplast ATP synthase changes its conformation depending on the transmembrane electrochemical potential difference of protons (delta mu H+). This conformational change is observable by measuring the change in the reactivity of Lys109 of the epsilon subunit of chloroplast-coupling-factor 1. Illumination of thylakoids increased the epsilon-Lys109 reactivity by a factor of 3-4 within 1 s. In the presence of ADP plus Pi, illumination of thylakoids increased the epsilon-Lys109 reactivity by a factor of only 2. Addition of ATP in the post-illumination dark or in the light after prior illumination increased the epsilon-Lys109 reactivity depending on the concentration of coexisting NH4Cl. ATP hydrolysis at high level was observed irrespective of the epsilon-Lys109 reactivity.