200 



P. M. Ray 



curves of lAA destruction, since such measurements are used widely 

 not only as a basis for interpreting the mechanism of lAA oxidation, 

 but also in physiological experiments in which lAA destruction is 

 involved. The phenomena have been investigated in experiments 

 performed with the lAA-oxidizing enzyme of Omphalia flavida (4, 5). 



When lAA is added to a peroxidase capable of oxidizing it, a 

 characteristic lag or induction phase precedes attainment of a rapid 

 reaction rate. This is illustrated with the solid line in Figure 1. It 

 appears to be due to the fact that the reaction medium does not con- 

 tain, initially, concentrations of the above-mentioned oxidation inter- 

 mediates (such as H2O2) great enough to allow a substantial rate 

 of oxidation. If H0O2 is added initially, no induction phase is ob- 

 served; instead the reaction is occurring rapidly at the earliest pos- 

 sible observation, as shown by the broken line in Figure 1. Evidently 

 HoO., is either a reaction intermediate, or it can give rise to the 

 actual intermediates rapidly. 



Under different conditions and with different enz\me preparations 

 it is to be expected that the initial content of oxidation intermediates 

 Avill vary. The initially observed rates of lAA destruction, as well 

 as how pronounced the induction effect is, will vary accordingly, 

 quite apart from variations in enzyme activity and effects of cofactors 



o 

 o: 



W 



o 



< 

 < 



10 



20 



30 



TIME MIN. 



Fig. 1. Illustration of the kinetic phases of enzymatic I.-\.\ oxidation observed with 

 and without addition of H.Oo. In this example, the initial lAA concentration 

 was 2 X 10-*M, and the top of the figure represents destruction of all the lAA. 

 At zero time and at the arrow 5 x 10-"A/ H.O, was added to tiie sample shown 

 l)v the broken line. 



