390 



CHLOROPLASTS AND CHROMOPLASTS 



CHAP. 14 



Table 14.IX 

 Chlorophyll-Protein Ratio in the Chloroplasts 



" Molecules chlorophyll per Svedberg unit of protein (molecular weight 17,000). 

 * Calculated by assuming 1% chlorophyll in total dry matter. 

 'About 10 in young leaves; about 5 in old leaves. 

 <* Depending on age and season. 



Table 14. IX shows the results of the determination of the ratio 

 of protein to chlorophyll in the chloroplastic matter by different ob- 

 servers. The last two columns give the number of chlorophyll molecules 

 for each Svedberg unit of protein. The results disagree considerably. 

 The values which are supposed to apply to chloroplasts as a whole are 

 higher (instead of lower) than those purported to represent the compo- 

 sition of the grana alone. If we believe the conclusions of Mommaerts 

 and Neish, each chlorophyll molecule in the grana could be associated 

 with an individual protein unit (as in hemoglobin and cytochrome c). 

 If Menke, Granick, Bot and Hanson are right, there is not even enough 

 protein in the whole chloroplast to provide each chlorophyll molecule 

 with its own protein "unit." 



An independent estimate of the ratio of chlorophyll to protein can be 

 obtained from microphotographs which show that not more than 20% 

 of the total leaf volume is taken up by chloroplasts; Menke's value (18% 

 chloroplast matter in the leaf) may be near the truth. According to 

 figure 39 (and similar pictures found elsewhere in the literature), not 

 more than 30-40% of the chloroplast volume is taken up by grana 

 (100 grana with a diameter of 0.5 ju must occupy about 5 fx^ in an average 

 chloroplast whose total volume is 20 fx^) ; thus, the grana should contain 

 not more than 10% of the total material of the leaf. This makes it 



