35G 



B. KOK 



The Rfm vs. U plots appeared to be linear over a range of short 

 dark times (e.g., in some cases at 30°C. beyond /<« = 5 m sec. and much 

 longer at low temperatures) and were of complex character in the 

 range of long dark times. Photosynthesis thus proceeds for a while at 

 full saturation rate after the light is extinguished. This initial zero- 

 order character of the reaction implies that the "half-times" as, e.g., 

 observed by Emerson and Arnold (4) and confirmed by us, have no 



xio 



12 



10 



o 



Mo— 1» 



M,_2-;:' 



10 



20 



if 



30 



— ♦ m.»»c. 



Fig. 3. Maximum flash j-ield as a function of flash time measured at two tem- 

 peratures with Chlorella ceUs suspended in buffer mixture. Here td = 0.1 second. 

 After Kok (3). 



direct significance in terms of velocity constants. The maximum 

 flash yield (C/o for tf -^ 0, U -^ ^) is independent of temperature. 

 The first conclusion to be drawn is that the primary photochemical 

 product is a stable one. Intensity-rate curves, as measured in ex- 

 periments mentioned under (3), were of an exponential shape, i.e., the 

 primary photochemical product is formed in a one-quantum process. 

 Thus in a single short flash one light quantum can be stabilized per 

 200 to 500 chlorophyll molecules ([/o = 2 to 5 X lO"" 02/Chl), if we 

 accept a quantum yield (/> = 0.1. 



The Rfm vs. tf plot (cf. U)) yields a good deal more direct informa- 

 tion : 



