The relation of electron transport and photophosphorylation to conformational changes in chloroplasts

1. The rate of the Hill reaction and photophosphorylation, and the ratio of ATP produced to the electron flow are shown to be strongly dependent on the solute concentration of the medium.

2. A large part, but not all, of the requirement for MgCl₂ or phosphate in photophosphorylation can be replaced by SrCl₂ or other solutes.

3. In two-stage photophosphorylation, solutes are required during the light-activation stage.

4. The presence of solutes causes marked changes in the packed volume of the chloroplasts, and their light-scattering properties. These changes are essentially complete within 1 min.

5. The effectiveness of solutes in enhancing the rate of electron transport and photophosphorylation parallels their effectiveness in inducing conformational changes in chloroplasts.

6. It is suggested that the solutes act by inducing a conformational change of the chloroplast structure which is more optimal for electron transfer and coupled phosphorylation.