210 



R. L. Hinman and P. Frost 



Table 1. Rates of oxidation of indole-3-acetic acid (lAA) and 7-(indole-3-)-«- 

 butyric acid (IBA) in various media. 



* Initial concentration of substrate = \0~^M. Ratio of H2O2 to substrate = 10 in 

 all experiments. 



t In the presence of \0~^M peroxidase; no H2O2 added. 



mixture of acetic acid and water the rate of increase of the peaks 

 was about the same as in the mineral acid system, although the initial 

 appearance of the peaks was still much slower (see Table 1). 



Decreasing the ratio of HoOo/lAA from 10:1 (which was the 

 ratio used for most of the experiments) to 1:1 did not affect signifi- 

 cantly the rate of growth of the peaks in the 250 m/x region, although 

 the initial appearance of the peak at 254 m^u, required somewliat 

 longer (5 min. when the ratio of 1:1). At a ratio of 1:2 the rate fell 

 off much more, although the final height reached by the peaks was 

 about the same as that of higher ratios, indicating that hydrogen 

 peroxide was not limiting. At still lower ratios of oxidant to lAA hy- 

 drogen peroxide was limiting, as shown by the fact that the maximum 

 absorption was much less than that attained at higher ratios. It is 

 not known whetiier the system also consumes oxygen, but from these 

 results it seems unlikely. 



SPECIFICITY OF THE MODEL SYSTEM 



One of the most striking features of tlic H^Oo/H*^ system is its 

 specificity. It appears to attack only those indoles which have a car- 

 boxyl group (or a potential carboxyl group) in the side chain at the 

 3-position, and for greatest reactivity the carboxyl carbon must be 



