568 



B. A. RUBIN 



300i 



250 



200 



150 



^ 100 



Oj, 7o 



Fig. 4. Dependence of the activity of the cytochrome oxidase of barley leaves 

 on partial pressure of oxygen and its connection with the localization of the 



enzyme in the cell, 

 (a) organoids, (b) homogenate. Age of plants in days, I — 8, II — 12, III — 18, IV — 22. 



The diagram (Fig. 5) gives grounds for supposing that the biological signi- 

 ficance of this changeover lies in its facilitating respiration of the fruit in falling 

 air temperature, as the value of Qio in the Fe- and Cu-proteins is considerably 

 higher than that in the oxidases which are not susceptible to poisoning. 



In the activation of 'cold-resistant enzymes' one may also include the adapta- 

 tion to its purpose of the substitution of cytochrome oxidase by polyphenol 

 oxidase u'hich is seen during the process of ripening of apples [20]. 



500 



§- 



J 400 



I 300 



200 



ë 



100 



10 



20 



30 



Fig. 5. Influence of temperature on the activity of respiration and of the respira- 

 tory enzymes of citrus fruits. 



(a) Lemon (Novogruzinskiï). (b) Tangerine (Unshiu). I — Total respiration. II — 



Residual respiration. The hatched area represents the amount of respiration 



suppressed by sodium azide. 



