RESPIRATORY SYSTEMS 63 



Manifestly temperature is also a controlling factor in respira- 

 tion, just as in almost all other biological reactions. The time 

 factor, which is correlated with temperature, must also be meas- 

 ured, as is indicated by Richter's experiments. The temperature 

 effect, apart from time, is strikingly shown in the classical experi- 

 ments of Muller-Thurgau [Lutman (1929)], involving Saccharo- 

 myces cerevisiae, in which all other conditions were identical and 

 fermentation was permitted to proceed until the maximum 

 amount of alcohol had been Droduced. These experiments yielded 

 the following results: 



RESPIRATORY SYSTEMS 



The general subject of respiratory enzymes is summarized in 

 an extensive compendium, Ergebnisse der Enzymforschimg by 

 Nord and Weidenhagen (1932-1939). It need only be stated 

 here that the main respiratory system in plant and animal cells 

 is composed of the following: Dehydrogenase— Substrate— Cyto- 

 chrome— Oxidase— Oxygen. Not only yeasts but also many, and 

 presumably all, fungi that live aerobically contain cytochrome. 



There is evidence that some other system operates in certain 

 anaerobic organisms. One of these systems is due to the presence 

 of glutathione, which can function as an oxidation-reduction sys- 

 tem. In the oxidized state it would appear thus: 



COOH COOH 



CHNH 2 ^ CHNH 2 



CH 2 CH 2 



CH 2 COOH COOH CH 2 



CO— NH— C— H H— C— NH— CO 



CH 2 — S — S — CH 2 



Glutathione (oxidized) 



