The Interpretation of Indole-3 -acetic Acid Oxidatioji 



203 



uration with HoOo have proved to be a much more reliable and re- 

 producible means of measuring enzyme activity than the steady 

 state rates, presumably because the HoOo saturation rate is not af- 

 fected by variations in the rates of initiation and termination. 



Finally, several examples exist in the literature of effects on lAA 

 oxidation rates which involve secondary complications on the steady 

 state rate, particularly effects on enzyme inactivation. Such effects 

 must be distinguished carefully from true kinetic effects, because 

 they cannot properly be used, in a kinetic sense, as evidence of the 

 reaction mechanism, and they may also have quite different sig- 

 nificance in physiology. 



It must be noticed that the early reaction phases illustrated in 

 Figure 1 take place over amounts of lAA oxidation too small to 

 be measured accurately by usual manometric methods, so that in 

 manometry one is dealing usually with the steady state (whether or 

 not HoOo is added) or with secondary rate complications. This lim- 

 its the usefulness of manometry in investigation of lAA oxidation. 



LITERATURE CITED 



1. Galston, A. W., Bonner, J., and Baker, R. S. Flavoprotein and peroxidase as 

 components of the indoleacetic acid oxidase system of peas. Arch. Biochem. 

 Biophys. 42: 456-470. 1953. 



2. Goldacre, P. L. Hydrogen peroxide in the enzymic oxidation of heteroauxin. 

 Austral. Jour. Sci. Res. B 4: 293-302. 1951. 



3. Maclachlan, G. A., and Waygood, E. R. Kinetics of the enzymically-catalyzed 

 oxidation of indoleacetic acid. Canad. Jour. Biochem. Physiol. 34: 1233-1250. 

 1956. 



4. Ray, P. M. Destruction of indoleacetic acid. IV. Kinetics of the enzymatic 

 oxidation. Arch. Biochem. Biophys. (In preparation). 



5. , and Thimann, K. V. The destruction of indoleacetic acid. I. Action 



of an enzyme from Omphalia flavida. Arch. Biochem. Biophys. 64: 175-192. 

 1956. 



6. Yamazaki, I., and Souzu, H. The mechanism of indoleacetic acid oxidase re- 

 action catalyzed by turnip peroxidase. Arch. Biochem. Biophys. 86: 294-301. 

 I960. 



