152 



E. R. Waygood and ('.. A. Maclnrhlan 



Induction Period, nnin. 



Fig. 2. Induction period in indole-3-acetic acid oxidation caused l)y catechol. Sys- 

 tems standard, catechol added prior to lAA. 



conceiuiaiions of 1.7 X 10-^ M and 0.5 X 10-^ M respectively. Cate- 

 chol and pyrogallol were reported also to inhibit the oxidation of 

 lAA catalyzed by horseradish peroxidase (3). Ascorbic acid is another 

 inhibitor that extended the lag by 45 min. at 3.33 X 10"^ ^^- ^^ is 

 noteworthy that an appreciable lag phase was induced by these in- 

 hibitors at concentrations as low as 10 •'* M. 



Rctarders 



Typical of the progress curves of oxygen uptake at varying con- 

 centrations of retarder are those shown in Figure 3, where riboflavin- 

 phosphate was progressively more inhibitory in darkness as its con- 

 centration was increased above 10-^ M. The progress curves for hy- 

 droquinone retardation were similar except that the systems at- 

 tained a low equilibrium (Figure 1). This was not due to enzyme 

 or cofador destruction, but apparently to a decline in the conren- 



