Chemical System for Oxidation of lAA by Peroxidase 



209 



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Fig. 2. Changes in the ultraviolet spectrum during the reaction of lAA (IQ-^M) 

 and HoOa (10-^) at pH 1. Solid lines: curve 1, 30 sec; 2, 1 hr.; 3, 5.5 hrs.; 4, 

 28 hrs.; 5, 72 hrs. Broken line lAA (10-*A/). Continuation of curves 4 and 5 over 

 range 0.8 to 1.8 absorbancy is given in reduced scale at lower left. 



The reaction of hydrogen peroxide with lAA is pH dependent. At 

 pH 1 the initial reaction is very rapid; the peak at 254 m^ is present 

 as soon as the spectrum is scanned (about 30 sec). From the accom- 

 panying table it is clear that the reaction rate decreases markedly 

 with increasing pH. In neutral or alkaline solution there is no change 

 in the spectrum of mixtures of lAA and hydrogen peroxide. This 

 agrees with Ray's (8) finding and confirms the earlier work of Siegel 

 and Weintraub (12), who showed by other methods that lAA is not 

 attacked appreciably by peroxides in neutral solution. 



When glacial acetic acid was used as the acidic medium, the peaks 

 at 248 and 254 m^ appeared, but the spectral changes were much 

 slower than in aqueous hydrochloric acid. However, in a 2:1 (v/v) 



