KINETIC ANALYSIS OF LIGHT RESPONSES 



373 



rate. A similar result may be inferred from the effects of low tem- 

 peratures where the ratio of on to off rate approaches infinity at 

 temperatures of liquid nitrogen (7). 



423 



1.0 



1 2 3 4 5 6 7 

 Intensity 



Fig. 2. Light-off /light-on rates for a component of 

 type c (423 m^u) and b or rhp (428 m/i) in R. rubntm 

 (900). 



A striking example of a light-off reaction that is more rapid than 

 the light-on reaction is afforded by the kinetics of cytochrome / of a 

 pale green mutant oi CMamydomonas, in response to illumination (11). 

 Here the ratio of the rates is about three (Fig, 3). 



554-540 m/j 

 Hfe°cH 



Fig. 3. Light-on/light-off kinetics for cytochrome / of 

 a pale green mutant of Chlcauydouioiias (674-11). (Cour- 

 tesy of Plant Physiol., 32, 557, 1957.) 



It should be noted that Amesz (12, also see 13) employs the light-off 

 reaction for the measurement of the quantum requirement for pyridine 

 nucleotide reduction in purple bacteria. Interestingly enough, Amesz 

 does not observe the need for establishing a steady state before cessa- 



