206 METABOLISM AND PHYSIOLOGY 



These data clearly indicate that MPM does not affect the primary 

 light-induced phase of photophosphorylation. 



The kinetics of photophosphorylation under intermittent illumination 

 at two different temperatures (15° and 26 °C) were also studied. The 

 half- life of delayed photophosphorylation was lengthened at the lower 

 temperature. It is concluded that a low rate of photophosphorylation 

 at a low temperature under continuous illumination results from a 

 slower dark process. 



Amount of ATP synthesis caused by a single flash 



The area covered by the curve of delayed photophosphorylation 

 corresponds to the number of ATP molecules formed per chlorophyll 

 molecule after a single flash. When the amounts of total delayed 

 photophosphorylation at different temperatures were compared, it was 

 found that the two values were approximately the same, though the rate 

 of photophosphorylation under continuous illumination was lower at 

 lower temperatures. The results are shown in Table 1. 



The presence of reagents such as HOQNO or MPM caused a 

 marked change in the rate of photophosphorylation, but the amounts of 

 total delayed photophosphorylation after a single flash in the presence 

 and absence of these reagents were approximately the same (Table 1). 

 These results indicate that the substances accumulating during the 

 short flash are consumed through dark processes, and phosphorylation 

 takes place accompanying the dark processes. Different temperatures, 

 HOQNO, and MPM do not affect the rapid photochemical process which 

 takes place during the flash. These factors influence the rate of dark 

 reactions of photophosphorylation. When the dark period is sufficiently 

 long, the total amount of delayed process is determined by the amount 

 of first product formed by a photochemical process during flash, hence 

 changes in rate of the dark process would have little effect on the 

 amount of total delayed photophosphorylation. This concept agrees well 

 with other data that indicated the presence of three steps for photo- 

 phosphorylation; i,e,, a rapid photochemical process, a second slower 

 process of electron transfer, and a third process of phosphorylation 

 coupled with the second process. 



The maximum amount of ATP synthesis per flash was determined 

 by combining the methods employing the sensitive recording pH meter 

 and the xenon flash tube illumination (20), An example of pH record- 

 ings is shown in Fig, 5, The single flash yield of photophosphorylation 

 at the saturation level and the rate of phosphorylation under continuous 

 illumination are tabulated in Table 2, Single flash yields are expressed 

 as molar ratios by comparison with the bacteriochlorophyll and cyto- 

 chrome concentrations. 



