380 



CHLOROPLASTS AND CHROMOPLASTS 



Table 14.VII 

 Catalatic Activity of Leaves (after Neish) 



CHAP. 14 



plast matter thus requires the presence of only 2.5 X lO"' g. catalase iron in 1 g. chloro- 

 plast matter. Since the content of iron in 1 g. dry chloroplast matter is from 3 X 10"^ 

 {Trifolium pratense) to 2.5 X 10"' g. (Elodea canadensis), an infinitesimal part of the 

 available iron is sufficient to build up the amount of catalase revealed by these ex- 

 periments. 



Peroxidase is present, according to Krossing (1940), mainly in the 

 water-soluble fraction of green leaves. Lubimenko (1928) postulated a 

 relation between the peroxidase activity of leaves and the formation and 

 decomposition of chlorophyll (c/. Chapter 15, page 431). 



(6) Carbonic Anhydrase 



Carbonic anhydrase catalyzes the hydration and dehydration of 

 carbon dioxide (page 176). Burr (1936) and Mommaerts (1940) found 

 no carbonic anhydrase in mashed leaves. Burr explained its absence by 

 the fact that all respiring plant cells are directly exposed to air, and that 

 therefore no necessity exists for an artificial increase in the velocity of 

 the carbon dioxide exchange between liquid and gas (this necessity arises 

 in the respiratory organs of animals, where carbon dioxide collected from 

 the whole body must be exchanged through a small surface). Neish 

 (19392), oj^ the other hand, observed a certain carbonic anhydrase 

 activity in separated chloroplastic matter and (to a lesser extent) also 

 in the cytoplasm, as shown by table 14. VIII. 



(c) Chlorophyllase 



This enzyme was discovered by Willstatter and Stoll (1913); it is an 

 esterase which catalyzes the exchange of phytyl for other alkyl radicals, 

 e. g., methyl or ethyl. In solutions which contain water, hydrolysis of 

 phytyl chlorophyllide may occur, leading to the corresponding mono- 

 carboxylic acid (chlorophyllin). The enzyme is present in leaves; the 

 observation that alcoholic extracts of leaves left standing in contact with 



