Influence of Oxygen on Radiation Effects 113 



that carboxypeptidase and the prosthetic group (alloxazine- 

 adenine dinueleotide) of D-amino-acid oxidase could be largely 

 protected not only by their specific substrates but also by a 

 variety of substances which are in no way structurally 

 related to these substrates. However, the problem of protec- 

 tion does not seem to have been examined in relation to the 



5000 



iOO 



4 5 



time (h) 



8 



Fig. 4. Percentage increase in Og uptake (= growth) of untreated and "low- 

 nitrogen" yeast (see text). 



(1) unirradiated control; 



(2) unirradiated "low-nitrogen" yeast; 



(3) "low-nitrogen" yeast irradiated in air and in nitrogen (24 kr.) 



oxygen effect, except by allowing bacteria to deplete their 

 medium of dissolved oxygen by oxidation of added substrate, 

 e.g. succinic acid, without renewing the used-up oxygen 

 (Stapleton, Billen and Hollaender, 1952), a procedure which 

 in effect does not differ from the removal of oxygen by reduc- 

 ing agents or by physical means. The enzyme used for the 



