E. R. WAYGOOD 



and 

 G. A. MACLACHLAN^ 



University of Manitoba 



I nhibit'Lon and Retardation of the 

 Enzymatlcally Catalyzed Oxidation of 



I ndole-3 -acetic Acid 



From studies described previously (5,6,9) on the enzymatic and 

 nonenzymatic breakdown of indole-3-acetic acid (lAA) in vitro, a 

 chain oxidative reaction sequence has been proposed for the peroxi- 

 dase catalyzed decarboxylation and oxidation of lAA. 



The chain reaction is initiated by a system consisting of either per- 

 oxidase or catalase and a specific type of phenolic cofactor which oxi- 

 dizes manganous (Mn^^) ^q manganic ions (Mn^^). propagation of the 

 chain is brought about by a reaction between lAA (S-COOH) (S — 

 skatole) which results in its spontaneous decarboxylation and the 

 consumption of one equivalent of oxygen to form a skatole peroxy- 

 radical as follows: 



Mn-3 + SCOOH > Mn-- + H^ + CO, + S- 



s. + Oo > so,- 



The skatole peroxy-radical is stabilized by an enzyme-controlled 

 peroxidation involving the phenolic cofactor (ROH) as hydrogen 

 donor, resulting in the latter's oxidation and the formation of an end 

 product of empirical formula (SO,H); viz. 



so... + ROH i«I^> SO,H + RO. 



catalase 



The phenolic radical (semiquinol) is capable of oxidizing manga- 

 nese and regenerating the reduced cofactor by the Kenten-Mann re- 

 action (4) until the supply of lAA is exhausted, e.g., 



Mn-2 _^ H- + RO- > Mn-3 _^ rqH 



In the present communication the inhibitory and retarding effects 

 of various substances on lAA oxidation are interpreted in terms of 



^Subsequently: Department of Botany. ITniversity of All^erta, Edmonton. Canada. 



[149] 



