372 PHOTOMECHANICAL CONSIDERATIONS 



Thus 



k Chi - k„ b" c'" (13) 



o 6 



601 Chi = k_ b" c'" (14) 



D 



Third, on cessation of illumination, Chi* falls to zero in a time 

 that is probably much less than 10"'* sec. From Equation 9 



"j- = k^ b" c'" (15) 



at 6 



In this way, the steady state flux is determined in moles/liter x sec of 

 cytochrome c. 



Also from Equation 14 



^ = k Chi = 601 Chi (16) 



dt o 



i.e., the initial rate of cytochrome reduction on cessation of illumina- 

 tion should be equal to the rate of activation of chlorophyll. 



EXPERIMENTAL RESULTS 



In view of the mathematical analysis above, it is important to ex- 

 amine the ratio of on-off rates in photosynthetic bacteria. In cyclic 

 electron flow, the initial rate of cytochrome reduction on interruption 

 of the illumination may be equal to the rate of cytochrome oxidation 

 (Equation 10) or, indeed, greater than the rate of cytochrome oxida- 

 tion (Equation 9). We have, therefore, in Fig. 2 plotted the ratio of on- 

 off velocities for an anaerobic suspension of/?, ruhnim, using a wave- 

 length of 423 m/i appropriate to cytochrome of type c and of 428 m/i 

 appropriate to cytochrome b or possibly rhp. It is seen over the range 

 of light intensities (the abscissa are proportional to light intensity) 

 that the on-off ratio at 423 m/7 is relatively constant but that at 428 

 m// is not. On this basis, cytochrome type c fulfills the requirements 

 for a component of cyclic electron transfer while cytochrome b or 

 rhp does not. A similar evaluation may be made of Fig. 3 of the ac- 

 companying paper (10) where, in the absence of glycerol, the on-off 

 rates for cytochrome of type c are similar, but in the presence of high 

 concentration of glycerol the on rate is much more rapid than the off 



