202 METABOLISM AND PHYSIOLOGY 



MATERIAL AND METHODS 



Chromatophores of the purple bacterium Rhodospirillum ruhrum 

 were isolated as reported previously (18). The rate of photophos- 

 phorylation was measured under near-infrared illumination with a 

 recording pH meter (21), or by phosphate analysis in the Reaction 

 medium (18). 



The light source used was a direct-current incandescent lamp 

 used in conjunction with an infrared filter (Wratten 88A) and a water 

 layer (5 cm thick). This filter combination passed near-infrared illum- 

 ination longer than 720 m/y in wavelengths. The light intensities used 

 were all above the level of saturation under continuous illumination, 

 unless otherwise stated. Flashing illumination was furnished by a 

 rotating sector (18). 



For the experiments on the maximum amount of ATP formation by 

 a single flash, a xenon flash tube (flash duration 0.5 msec) was trig- 

 gered at intervals of 60 sec. The light from the flash tube was filtered 

 through two Wratten 88A infrared filters. 



RESULTS 



Presence of delayed photophosphorylation after flash 



In the first type of experiments, the duration of light period was 

 kept constant at 1,45 msec, and lengths of dark periods were changed. 

 When the rates of phosphorylation were expressed in terms of phos- 

 phate esterified per illuminated time, we observed a remarkable rise 

 in the rate of phosphorylation with increasing dark period, indicating 

 the presence of delayed photophosphorylation after the flash. From the 

 curves (rate per illuminated time vs. dark period), we calculated by 

 differentiation the rate of phosphorylation after the flash, as shown in 

 Fig, 1, It was found that the decay of delayed photophosphorylation was 

 dependent on light intensity. The half-life of decay was shorter with 

 low intensity flashes and was longer with strong flashes. 



Light-induced phase of pJiotophosphorylation 



The rapid light-induced reaction which takes place in the short 

 flash was studied in the second type of experiment, where sufficiently 

 long dark periods were inserted between short flashes (181-1449 /isec), 

 and the duration of a light-dark cycle was kept constant at 8.70 msec. 

 The amount of phosphate esterified per minute per bacteriochlorophy 11 

 was plotted against the flash duration (Fig, 2), When the length of 

 flashes was sufficiently short, the rate of phosphorylation was pro- 

 portional to the flash length. The rate was greater under flashes of high 

 light intensity, but under continuous illumination the rate was identical 

 with these three light intensities (indicated in Fig. 2 by 8.70 msec light 



