Oxidation Systems of Organisms 



567 



chemistry of the Academy of Sciences of the U.S.S.R. it has been shown that 

 in immature apples 95% of the polyphenol oxidase activity is due to the plastids 

 and only 5% to the cytoplasm. At the time of complete ripeness of the fruit by 

 far the greater part of the polyphenol oxidase is in the cytoplasm (80%), only 

 about one-fifth of the whole enzyme content remaining in the plastids (Fig. 2). 

 In potato tubers in August 97% of the polyphenol oxidase is in the plastids 

 while in February they contain less than 30%. With M. Ladygina [19] I have 

 observed a similar picture while studying the cytochrome oxidase of barley 

 shoots. If, when the shoots were 8 days old, the proportion of cytochrome oxidase 

 concentrated in the organoids was 92%, than at 18 days this value wovild fall to 

 63% and at 22 days to 56%. Accordingly, the cytoplasm of the young plants, 

 which was almost free of enzyme became, in the course of 15 days, the repository 

 of almost half of the whole cytochrome oxidase activity of the cell (Fig. 3). 



50 



40 



30 



Ö 



's. 



20 



10 



10 12 14 IS 18 



Growth of shoots, days 



20 



22 



Fig. 3. Distribution of cytochrome oxidase in the leaves of barley at different 

 stages of growth. I, II and III as in Fig. 2. 



These findings are of interest in view of the fact that the localization of the 

 enzyme affects its dependence on the action of external factors. Ladygina's 

 experiments show, for example, that oxidation of c}n:ochrome by a suspension 

 reaches its maximum when the concentration of oxygen in the medium is as low 

 as 5-10%, while the oxidation of cytochrome by a preparation of organoids 

 continues to increase even when the partial pressure of oxygen is raised above 

 21% (Fig. 4). 



The causes of all these substitutions in the activity of the oxidative enzjntnes 

 have still not been thorouglily studied. There is reason to beheve that they have 

 an adaptive significance. 



The replacement, which has already been mentioned, of Fe- and Cu-proteins 

 by enzymes which are resistant to the action of respiratory poisons may serve 

 as an example. 



