110 



OXIDATION-REDUCTION POTENTIALS 



Evidence has also been adduced for the formation of hydrogen peroxide when 

 sulphydryl compounds, such as glutathione, are oxidised in the air : — 



2 GSH + O2 -> GSSG + H2O2. 



Wieland and his co-workers have succeeded in obtaining quantitative yields of 

 hydrogen peroxide in experiments with milk dehydrogenases, and Bertho and Gliick 

 -(1931) have obtained high yields of peroxide in bacterial cultures. 



Hydrogen peroxide is frequently produced as the result of the co-existence 

 •of " activated hydrogen " and molecular oxygen. McLeod and Gordon (1922, 1923) 

 found that pneumococcal cultures produced hydrogen peroxide which inhibited 

 bacterial growth. Avery with Morgan and Neill (1924) extended the study of 

 peroxide formation and Neill and Avery (1925) found that sterile extracts of 

 pneumococci produced peroxide when exposed to oxygen in the presence of 

 appropriate " hydrogen donators." That the presence of actively proliferating cells 

 is not essential for the formation of peroxide is in agreement with the author's 



• 0-4 ■ 



.0-3 



• 0-2 



• O-l 

 ♦O'O 

 -0-1 

 -0-2 



24 



30 



6 12 18 



Time (hours) 



Fig. 22 



Infusion broth cultures of pneumococcus, type II 



experiments (1930, 1). It was found that in aerated cultures of hasmolytic strep- 

 tococci reducing conditions were first established in the cultures but that after the 

 logarithmic phase of growth, when the organisms had ceased to proliferate actively, 

 oxidising conditions were established and peroxide could be detected both by its 

 reactions and by its eifect on the electrode potential. Peroxide did not accumulate 

 in cultures until after the active growth period when the number of living organisms 

 was decreasing. 



McLeod incHnes strongly to the \aew that anaerobic organisms are unable to 

 multiply because in the presence of air they would produce hydrogen peroxide, which 

 would immediately inhibit growth. The greater the reducing power of the cell, in 

 McLeod's opinion, the greater the tendency to form peroxide, hence the anaerobes 

 would form peroxide readily. Many aerobic bacteria form catalase (Callow, 1923) 

 in their cultures. In these cases, therefore, peroxide cannot accumulate as it is 

 decomposed immediately it is formed. On the basis of the facts available McLeod 

 classified organisms as follows : — 



(i) Potential peroxide producers. Devoid of catalase. 

 to peroxide. The anaerobes. 



Verv sensitive 



