638 



LIGHT AND LIFE 



i 



Effect of Chlorophyll Concentration 



The effect of chloroplast concentration on the rate of formation 

 of TPNH is shown in Fig. 2 (lower curve) . It can be seen that the 

 rate of photochemical reduction is linearly proportional to the chloro- 

 plast concentration. Similar results have been reported previously 

 with grana in place of chloroplasts (22). Several interpretations of 

 this observation with grana have been discussed elsewhere and need 

 not be repeated here (22) . 



It is interesting that the addition of Mg++ increases the rate of 

 TPN reduction at each of the chloroplast concentrations tested (Fig. 

 2, upper curve) . This effect of Mg++ is not completely understood 

 at the present time. 



Effect of Enzyme on Photosynthetic Phosphorylation (see paper 

 by Jagendorf, in tliis symposium, for additional information) 



The effect of the enzyme on photosynthetic phosphorylation is 

 shown in Table 4. In these experiments both the formation of 

 TPNH and the decrease in inorganic phosphate were determined. 

 It is clear from these data that the addition of enzyme stimulates 

 both the formation of TPNH and photosynthetic phosphorylation. 

 These results are in agreement with the findings of Arnon et al. (3) 

 that the addition of an aqueous extract of whole chloroplasts to 



o 



ro 



50 100 150 200 



MICROGRAMS CHLOROPHYLL 

 Fig. 2. Effect of chloroplast concentration on the rate of reduction of TPN. Each 

 reaction mixture contained 150 ^moles of Tris buffer, pH 7.2, 0.r75 ^.moles of TPN, 

 0.4 unit of enzyme, and chloroplasts equivalent to varying amounts of chlorophyll. 

 Final volume was 3 ml; illumination for 5 minutes at 24 °C. Lower curve, no MgClj; 

 upper curve, 5 ^^moles of MgClj. 



