PHOTOPHOSPHORYLATION IN FLASHING LIGHT 



205 



in the presence of HOQNO, is probably due to inhibition of electron 

 transfer between cytochromes b and c (8), 



The rate of photophosphorylation is markedly increased by MPM 

 under sufficient illumination (22,23), The rates of phosphorylation 

 after the flashes were calculated from a flashing light experiment. A 

 remarkable acceleration of decay of delayed phosphorylation by the 

 added MPM was noticed. The effect of MPM on the kinetics of delayed 

 photophosphorylation was like a reversal of the effect caused by 

 HOQNO. 



APj/min/BCHL 

 8 



8.70msec. Cycles 

 16,000 IUX + 88A 



Control 



msec. Light Period 



Fig. 4. Effect of MPM on photophosphorylation in Type B illumination. Ordinate: 

 Pi esterified in moles/min/naole bacteriochlorophyll. Abscissa: length of light 



period. 



no MPM: 



-,1.1 X 10--^ M MPM. 16,000 lux + 88A filter, 28°C. 



In the second set of experiments, the effect of MPM on the light- 

 induced phase of photophosphorylation was investigated. The rate of 

 phosphorylation was proportional to the length of the flash when the 

 flash duration was sufficiently short. The tangents of these two 

 curves were identical in the absence and presence of MPM (Fig. 4). 



