KINETIC ANALYSIS OF LIGHT RESPONSES 371 



b" + c'" —^ b'" + c" (7) 



Thus, the cycle is completed through the chain of carriers. 



Differential equations. 



The differential equations for the rates of electron transport are 

 very similar to those for the respiratory chain (8) with two important 

 exceptions. First, the activation of chlorophyll by light results in an 

 average rate of conversion of chlorophyll to its activated state: 



^-^^ = k Chi - k, Chi* c" (8) 



dt o 1 



Second, the rate of the primary electron transfer reaction consists 

 of the rate of oxidation of reduced cytochrome cl by activated chloro- 

 phyll minus the rate of reduction of oxidized cytochrome c by reduced 

 cytochrome h: 



- ^ = k, Chi* c" - k^ b" c'" (9) 



dt 1 6 



Without a detailed study of the remaining equations, it is possible 



dc" 

 to draw the following conclusions. The observation that - — rr- can be 



accelerated by addition of glycerol suggests that the term kg b" c'" 

 in Chromatium is not negligible or that glycerol acts by affecting kg 

 to a greater extent than kj. From observations of the effect of phenyl 

 mercuric acetate on the steady state level of cytochrome c (9), it is 

 clear that cytochrome c is highly reduced. But very little is known 

 about the steady state level of cytochrome h, and it cannot be assumed 

 at present that b" = 0. Inhibition of electron transfer by glycerol 

 appears to cause the term ks b" c'" to diminish and under such ideal 

 conditions we have the first useful expression: 



- -5^ = k, Chi* c" (10) 



dt 1 



Second, in the steady state, — r— = and --r — = 



and 



k, Chi* c" = k^ b" c"' (11) 



1 b 



k Chi = k, Chi* c" (12) 



o 1 



1 In these equations we assume that c"'is zero in the dark. 



