156 



E. R. Way good and G. A. Maclachlan 



The Effect of Light and Riboflavin 



As was demonstrated previously with the catalase-dichlorophenol 

 system (8), blue light, absorbed by riboflavin, overcame the retarding 

 effect of riboflavinphosphate on the wheat leaf system in the presence 

 of any one of the cofactors (Table 1). The rate of oxidation of illu- 

 minated systems containing riboflavin was no greater than the rate in 

 darkness without riboflavin except when the natural factor (9) was 

 used. In the absence of riboflavin, light had no effect on the system. 

 The augmentation of the dark rate in the illuminated system con- 

 taining the natural factor and riboflavin may have been due to the 

 combined effect of riboflavin and light in overcoming an inhibitor 

 present in the partially purified extract of the former (cf. 8). 



The alleviation of the riboflavin effect depended on the quality 



140 



-^CVJ 



Fig. 5. EfTect of quality and iiuciisily of light on ribofUu in inhibited indole-3- 

 acetic acid oxidation. Standard system plus 6 /iM riboflavinphosphate. Color and 

 intensity of light (in foot candies at surface of reaction vessel) indicated in diagram. 



