158 



E. R. Waygood and G. A. Maclachlan 



TIME, min. 



Fig. 6. Oxygen uptake of systems containing excess riboflavin with and without 

 inclole-3-acetic acid: A, standard system phis 6 fiM riboflavinphosphate in bUie 

 light (220 foot candles) indole-3-acetic acid = 3.33 jxhl = 79 /^l. O2 (molar equiv- 

 alence); B, oxygen uptake of A minus uptake of C; C, same as A minus indole-3- 

 acetic acid; D, same as C in darkness. 



higher light intensities or when the riboflavin concentration was 

 increased, e.g., to twice the molar concentration of lAA. 



DISCUSSION 



In order to inhibit such an autoxidation sequence a substance 

 must interrupt a chain of interdependent steps by reacting with an 

 essential intermediate of the system. Inhibition may be expressed 

 in either of two ways: (1) as an extension of the induction period 

 which occurs in all autoxidations; or (2) as a retardation of reaction 

 velocity. As pointed out by Waters and Wickham-Jones (7) these ef- 



