Metabolism and mode of action 



is generally considered to be a phenol reagent. Thus, we have tentatively 

 concluded that the product may be a phenolic aminoacetophenone. Since 

 neither OFA nor OAA is converted to the product, the hydroxylation step 

 (presumably at the No. 5 or 6 position on the indole ring) must precede the 

 ring cleavage between the No. 2 and 3 carbons {Figure 5). 



Our understanding of the physiological significance of this conversion is 

 limited to the observation that neither OAA, OFA, nor the authentic 

 oxidation products appear to have any marked effects on growth in the pea 

 epicotyl section test. Thus, lAA oxidase, if it is operative in tissue, results in 

 the diminution of growth by the lowering of the effective auxin level. 



lAA 



Hydroxy-IAA 



<^^ 



Hydroxy-o-Formamido 

 Benzoylacetic acid 







II 



C-CHo— COOH 



CH2— COOH 



"N' 

 H 



■NH2 



Hydroxy- OAA 



^ ^ Hydroxy- OFA 



Figure 5. A possible scheme of oxidation oflAA and a possible product satisfying all experimental data. 



THE NATURE OF INDOLEACETIC ACID OXIDASE AND ITS INDUCTION BY lAA 



The enzyme complex which we refer to as indoleacetic acid oxidase was 

 discovered by Tang and Bonner (1947) in etiolated peas and has since been 

 shown to exist in other higher plants (Wagenknecht and Burris, 1950; 

 Gortner and Kent, 1953; Jensen, 1955; Pilet and Galston, 1955) and in 

 fungi (Sequeira and Steeves, 1954; Tonhazy and Pelczar, 1954). It 

 appears certain that the enzyme differs from plant to plant and is absent 

 from some tissues (Piatt, 1954) ; but we have limited ourselves to an attempt 

 to understand its make-vip in one plant, Pisiim sativum, and in some closely 

 related legumes. 



The essential facts which need to be considered in understanding the nature 

 of the lAA oxidase system in peas, and the principal deductions to be drawn 

 from them are: 



(a) The enzymatic activity is inhibited by crystalline catalase (Goldacre, 

 1951), implying the intervention of H2O2 somewhere in the system {Figure 6). 



{b) The inhibition conferred by catalase can be reversed by light (Galston 

 and Baker, 1951), the action spectrum for such a light activation resembling 

 the absorption spectrum of flavoproteins. Since reduced flavin enzymes are 



224 



