p. L. GOLDACREi 



C.S.I.R.O., Division of Plant Industry, 

 Canberra, Australia 



The I ndote-3 -acetic Acid Oxidase-Peroxidase 



of Peas 



I want to give a brief outline of the structure and properties of the 

 enzyme known as indoleacetic acid oxidase from peas. This enzyme 

 system has suffered somewhat from the publication of experiments 

 which are ahnost relevant, and from unsympathetic comparisons of 

 preparations from diverse tissues, with the result that the literature 

 is conflicting, both in substance and in detail. I want to try to recon- 

 cile some of these divergences, and present a generalized picture. 



Firstly, indole-3-acetic acid (lAA) is inactivated by plant tissues. 



Secondly, macerates from many plant tissues can inactivate lAA 

 by oxidation (9, 17, 19) . Whether such preparations have real signifi- 

 cance for the growth of the plant or are artifacts of maceration (1,2) 

 is a question discussed elsewhere. 



Thirdly, it seems likely that there exists a number of possible 

 ways in which lAA is enzymatically destroyed. Evidence is accumu- 

 lating that there are several alternative systems. These may vary 

 from tissue to tissue or may coexist to varying degrees in the same 

 tissue (8, 9). Any postulated role assigned lAA oxidase for a particu- 

 lar tissue must take into account the properties of those enzyme sys- 

 tems present in that tissue. 



The lAA oxidase system of etiolated pea epicotyls or roots is pres- 

 ent entirely in the nonparticulate fraction (8). Each mole of lAA 

 disappearing is accompanied by the consumption of one mole of oxy- 

 gen and the production of one mole of carbon dioxide (17, 19). The 

 stepwise reduction of oxygen, with the intermediate formation and 

 subsequent utilization of hydrogen peroxide, is inferred from the 

 total inhibition of lAA destruction by peroxide-consuming addenda. 



^Deceased April 16, 1960. 



[143] 



