ENEEGY SUPPLY OF THE CELL 97 



Most culture media are reducing solutions, even when 

 sterile. All organic compounds can be oxidized, and 

 it might be expected that they all produce a reduction 

 potential. Only reversibly oxidizable compounds can 

 produce a measurable potential, however. Most organic 

 compounds are quite stable; a sterile solution of sugar 

 or of amino acid remains unchanged. This is only a 

 false equilibrium, however, for Warburg (1921) could 

 demonstrate that amino acids are slowly oxidized in 

 aqueous solution at body temperature if Merck's blood 

 charcoal is added, and Meyerhof and Weber (1923) 

 could oxidize, in the same way, not glucose as such, but 

 the glucose phosphate. 



At the same time, Hopkins (1921) had found gluta- 

 thione to be the cause of auto-oxidation in cells, and the 

 SH group to be the essential part of the oxidizing property 

 of this molecule. In the presence of glutathione, or 

 cysteine, or thioglycollic acid (all possessing the SH 

 group) organic matter, such as yeast juice, or other cell 

 debris, takes up much more oxygen than corresponds 

 to the amount of sulfhydryl-compound added. In 

 other words, these compounds act as oxygen-catalysts, 

 and overcome the false equilibrium of organic compounds 

 in solution. Culture media are mixtures of many 

 organic compounds, and it has been observed quite 

 early (Th. Smith, 1896) that sterile broth will combine 

 with oxygen, and will reduce methylene blue if protected 

 from air. Coulter (1929) measured the reduction poten- 

 tial of a meat infusion broth (pH 7.6) electrometrically, 

 and found that the potential in air was between -1-0.150 

 and +0.250 volts. When H2O2 was added, it rose to 

 more than 0.400 volts. When nitrogen gas was bubbled 

 through the broth to remove the oxygen, the potential 

 gradually decreased (see Fig. 10) and in all of his experi- 



