1604 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



steady photogalvanic potential) remains the same. The kinetic signifi- 

 cance attached to this result of Wessels, will be related below under "Kinetic 

 Theories." 



Yield in Flashing Light. The data on the yield of the Hill reaction 

 is flashing light in relation to flash energy and duration of dark intervals 

 (Clendenning and Ehrmantraut 1951; Gilmour d al. 1953) were presented 

 in chapter 34, section B7. 



Kinetic Theories. Kinetic analysis of the Hill reaction — of the type of 

 that attempted in chapters 27 and 28 — is an even more uncertain undertak- 

 ing than that of photosynthesis, because the deterioration of the activity of 

 chloroplasts with time makes quantitative reproducibility of the data 



10 



15 20 25 30 35 iO 45 50 

 »• time In minutes 



Fig. 35.23A. Influence of chloroplast concentration on change in redox potential 

 of suspension containing 2,6-dichlorophenol indophenol (^'o = —0.255 volt) 

 (Wessels 1954). Chloroplast concentrations: soUd line, 4; dashed line, 2; 

 dashed-dotted line, 1. 



questionable. In the case of live Chlorella cells (c/. part C below) there is 

 no equally rapid deterioration, but the only oxidant successfully used so 

 far, quinone, has a "self-poisoning" effect which complicates the kinetic 

 picture considerably. 



A priori, the kinetic treatment of the Hill reaction should be simplified 

 by the elimination of the complex carbon dioxide factor. However, the dif- 

 fusion of the oxidant to the chloroplasts may sometimes become the limit- 

 ing factor. Supply barriers are, of course, reduced by the greater aisper- 

 sion of the material and the absence of cell walls ; but the necessity to use 

 some oxidants in a very dilute form (this applies to dyes because of their 

 strong light absorption; and to quinone — with live cells — because of its 

 poisonous effect) increases the possibility of "oxidant limitation." 



Assuming the absence of such limitations, the parts of the discussion in 



