THE CHLOROPLAST ENZYMES 



379 



not quite agree with Neish's statement that 60% of the chloroplast iron 

 (from Trifolium pratense) is soluble in dilute (10%) acetic acid. 



As to the chloroplast copper, Neish (19W-) found that most of it 

 (90-100%) is insoluble in 10% acetic acid and is probably present in the 

 form of organic complexes. 



4. The Chloroplast Enzymes 



In chapters 6, 7, 8, and 10, we discussed the catalytic reactions in 

 photosynthesis and found that the photosynthetic apparatus probably 

 contains (at least) the following catalysts: (1) Ea, a cyanide-sensitive 

 carboxylase (Franck's "catalyst A," possibly located outside the chloro- 

 plasts); (2) an enzymatic system (including Franck's "catalyst B") 

 involved in the transformations which lead from the carbon dioxide- 

 acceptor complex to carbohydrates (mutases, oxidoreductases, polymer- 

 izing enzymes), part of which system is specifically affected by dinitro- 

 phenol; and (3) an enzymatic system involved in the conversion of the 

 primary photochemical oxidation product into free oxygen (Franck's 

 "catalyst C"). The latter system includes (at least) two enzymes 

 which, in several of our schemes in chapter 7, have been designated by 

 Ec and Eo, respectively. Both these catalysts appear to be specifically 

 affected by hydroxylamine and o-phenanthroline. 



What is known empirically about the enzymes in green plant cells 

 has not much relation to these hypothetical catalysts. The available 

 evidence deals with the well-known enzymes like catalase, carbonic 

 anhydrase, phosphorylase, amylase, maltase, and invertase, which either 

 have no relation to the synthesis of carbohydrates at all, or intervene 

 only in its ultimate stages (formation and decomposition of sucrose and 

 starch). The occurrence of carbohydrate-transforming enzymes in green 

 leaves was briefly discussed in chapter 3. Here, we shall add a few data 

 on other enzymes, taken mainly from the work of Neish (1939) and 

 Krossing (1940) on separated chloroplastic matter. 



(a) Catalase and Peroxidase 



Catalase, the enzyme which causes the dismutation of hydrogen 

 peroxide, is found in both colorless and green plant organs. The relation 

 between photosynthesis and catalase activity was discussed in chapter 11 

 (page 284). Neish (1939-) has measured the catalatic activity of sepa- 

 rated chloroplast matter and compared it with that of whole mashed 

 leaves (Table 14. VII). According to this table, all the catalase of green 

 leaves is concentrated in the chloroplasts. Krossing (1940) on the other 

 hand, found catalase both in the chloroplasts and in the cytoplasm. 



The efficiency of catalase is about 10* moles hydrogen peroxide decomposed per 

 sec. per gram atom iron. The Uberation of 12 mm.^ oxygen per 2 min. per 1 mg. chloro- 



