Photoreactions of Chloroplasts in a Glycine Medium

The rate of photoinduced electron transport in a medium containing glycine as the major salt was very low. It was dramatically increased by low concentrations of monovalent salts (2–4 mM) to rates typical of uncoupled systems. Further increase in salt concentration (beyond 15–20 mM) cause a sharp decrease back to “coupled” values. Salts of divalent ions, like Mg²⁺ were even more effective in the “recoupling” process (0.1 mM). When low amounts of Mg²⁺, phosphate and ADP were added to the glycine medium, photophosphorylation proceeded initially at high rates but stopped after a certain amount of ATP was accumulated. This effect was traced to a complete inhibition by the ATP formed of any further phosphorylation. The concentration of ATP needed to inhibit increased sharply with an increase of the salt concentration in the medium. ADP exhibited a similar inhibitory effect but higher concentrations were required. At concentrations where ATP inhibited phosphorylation, proton uptake was not affected.