Chemical System for Oxidation of lAA by Peroxidase 211 



separated from the indole ring by one other carbon atom, as in lAA. 

 This generalization is based on the following observations. (All ex- 

 periments were carried out at pH 1 with a mole ratio of H2O2/IAA 

 of 10:1.) 



(1) The spectrum of skatole remained unchanged for 25 hrs. 



(2) The spectrum of y-(indoIe-3-)-??-butyric acid (IBA) underwent rela- 

 tively slow changes, but peaks at 248 and 254 m^u, were distin- 

 guishable after 12 hrs. and reached maximum absorbancy in 48 

 hrs. (Figure 3). A shoulder with its center at 290 m/x appeared be- 

 tween 24 and 48 hrs., corresponding to the maximum observed 

 at 295 m^ when lAA was subjected to prolonged treatment with 

 the H0O2/H+ system. 



(3) The spectrum of (3-(indole-3-)propionic acid (IPA) underwent a 

 very slow increase in absorption in the 230 to 260 nifj^ region, 

 while the indole peak at 280 rrifx slowly declined. No specific peaks 

 appeared (Figure 3). 



(4) The spectrum of a,a-dimethylindole-3-acetic acid in which, as 

 in lAA, the carboxyl group and the ring are separated by one 

 carbon, changed more rapidly than did the spectrum of lAA, and 

 was complete in 18 hrs. The new peaks were at 248, 259, and 293 

 m^ (Figure 3). In this case the peak at 293 m^ was formed about 

 as rapidly as those at lower wave lengths, whereas with lAA the 

 low^er peaks reached their maximum heights first, and the peak at 

 295 m^ required an additional 48 hrs. for complete formation 

 (Figure 2). 



(5) The spectrum of 2-phenylindole-3-acetic acid changed rapidly and 

 was complete in about 4 hrs. The spectral shifts are not directly 

 comparable to those of the lAA reactions because the absorp- 

 tion spectra of lAA and of 2-phenyl-IAA are quite different, as 

 are those of their oxidation products. Nevertheless, it is signifi- 

 cant that the spectrum of 2-phenylskatole, which lacks the car- 

 boxyl group, was unchanged after 25 hrs. in the H2O2/H+ system. 



It is clear from these results that the Ho02/H^ system is selective 

 in its attack of indoles. Any reaction which is limited to lAA and re- 

 lated compounds would be of interest in considering the biological 

 activity of lAA. The close relationship of the products of the chemical 

 reaction and of the enzymatic reaction makes the chemical system 

 considerably more significant. 



THE COURSE OF THE CHEMICAL REACTION AND 

 THE NATURE OF THE PRODUCTS 



Although final answers have not been obtained to the questions 

 of the detailed pathway of lAA oxidation in the H2O2/H+ system and 



