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The Relation between Photophosphorylation and Delayed Light Emission in Chloroplasts ¹

^a Department of Botany, Imperial College, London SW7, England

One millisecond delayed light emission has been studied in isolated coupled lettuce (Lactuca sativa var. romaine) chloroplasts. Delayed light emission was increased upon addition of ferricyanide or 2,3,5,6-tetramethyl-p-phenylene diamine. In the presence of ferricyanide, the magnitude of the signal was increased by the addition of ADP (in the absence of orthophosphate), ATP, DI0-9, or phlorizin. The signal was also increased by the addition of NaCl and by the addition of NH₄Cl in the presence of a high NaCl concentration. The signal of delayed light emission was decreased by the addition of gramicidin, valinomycin, and by the addition of NH₄Cl in the presence of a low NaCl concentration.

Phosphorylation, whether started by addition of ADP or by addition of glucose plus hexokinase plus ATP, caused a significant decrease in delayed light emission. It was concluded that the magnitude of delayed light emission reflects the size of the proton motive force across the thylakoid membrane. Calibration of delayed light emission by creating KCl gradients indicated that the value for the electrochemical potential gradient for H⁺ in the presence of ferricyanide was at least 155 millivolts decreasing to 134 millivolts after the onset of phosphorylation.

³ Present address: Department of Biochemistry, Cornell University, Ithaca, N.Y. 14850.

¹ This work was supported by the Science Research Council, the Royal Society, and the Central Research Fund of the University of London. Also supported by a short term EMBO grant to J.N.