KINETICS 



1595 



TABLE 35.x 

 Maximum Initial Rate of Hill Reaction, H""^^- (in Mm.^ O2 per Mg. Chi per Hr.) 



" Highest rates with lamb's quarters, millet, chard, lettuce, spinach, flax (cf. section 

 B2 for details). 



* Cf. section B2 for comparison of species. 



tions between the (common) oxidation product (oxygen or a "photoper- 

 oxide") and the (individual) reduction products. Back reactions do not by 

 themselves lead to light saturation, but if the maximum rate in strong light 

 is determined by the deficiency of a "finishing" or "stabihzing" catalyst, 

 then a difference in the reducing power of the various reduction products 

 can affect the turnover of this catalyst, and thus influence the saturation 

 level. Aronoff (1946-) found three different hght curves (fig. 35.21), 

 H = /(/), for the rate of oxygen liberation by "grana" from spinach chloro- 

 plasts, as function of light intensity, for three different quinones. A dif- 

 ferent yield in weak light, as well as a different saturation level, could be 

 attributed to differences in the reducing power of the three hydroquinones ; 

 but in this case the order of the curves should be the same in strong and in 

 weak hght. The crossing-over of these curves, shown in fig. 35.21, 

 remains unexplained. 



Effect of Concentration of the Oxidant. In photosynthesis, the effect of 

 the factor [CO2] on the rate (discussed in chapter 27) was represented by a 

 saturation curve, with evidence of inhibition at very high concentrations. 

 The initial increase in rate with [CO2] appeared to be, to a considerable de- 

 gree, the result of supply processes; we had to leave the question open 

 whether supply effects can be eliminated, and an "intrinsic" CO2 saturation 

 curve of photosynthesis obtained, reflecting the participation of carbon 



