Inhibition and Retardation of the Oxidation of lAA 



151 



Table 1. Inhibition and retardation of indole-3-acetic acid oxidation in the 

 presence of catechol, hydroquinone, and riboflavinphosphate. * 



■ Concentrations: Catechol 1.5 X 10-^ fiM; hydroquinone 6 X 10/ ^Mj ribo- 

 flavinphosphate 3.3 X 10-1 f,M; resorcinol, DCP, phenol, 1.5 ^M; maleic hydrazide 

 30 txM, natural factor 0.15 ml. Vol. 3.0 ml. blue light, 220 foot candles. 



a short induction period and a subsequent rapid rate of oxidation 

 that gradually decelerated until theoretical molar equivalence was 

 attained (Figure lA). The rate of oxidation was influenced by sub- 

 stances that either extended the induction period, e.g., catechol at 

 10-5 M (Figure IB), or retarded the rate of oxidation from the out- 

 set, e.g., riboflavinphosphate at 2.1 X 10"' M (Figure IC) or hydro- 

 quinone at 1.5 X 10-^ M (Figure ID). 



The above experiments were performed using resorcinol as co- 

 factor of the oxidation, but the effects of these inhibitors and re- 

 tarders were the same in the presence of other cof actors (Table 1). 

 Catechol resulted in an extension of the induction period the length 

 of which depended on the cofactor used. On the other hand, the 

 degree to which hydroquinone and riboflavinphosphate retarded the 

 oxidation of lAA was almost independent of the nature of the co- 

 factor. The systems retarded by riboflavinphosphate, but not those 

 retarded by hydroquinone, were rendered fully active by illumination 

 (Table 1). 



Extension of the Induction Phase (Inhibitors) 



The relationship between the concentration of catechol in the 

 system and the length of the induction period is shown in Figure 2. 

 The data show that the oxidation of lAA would never occur above 

 a catechol concentration of 1.9 X 10-^ M. However, this value can 

 be regarded only as approximate since the age of the solutions and 

 the enzyme used were found to influence the length of the lag phase 

 induced by catechol (9). 



A similar inhibition was caused by pyrogallol and the flavonoid 

 pigment rutin, both of which extended the lag phase by 25 min. at 



