A fluorometric method for the kinetic assay of indole-3-acetic acid oxidase.

The oxidation of IAA by peroxidase (1) and by more specific oxidases (2) leads to the formation of products which may have physiological activity (3, 4). The colorimetric estimation of IAA oxidation products involving reaction with p-dimethylaminocinnamaldehyde (DMACA) is reported to be more sensitive than other end point determinations such as the Salkowski and Ehrlich procedures which monitor the disappearance of IAA (5). These methods are end point procedures and, as such, are awkward and time consuming and present difficulties in obtaining kinetic data and measuring lag times. IAA oxidation has also been monitored by measuring ¹⁴CO₂ released from [1-¹⁴C] IAA (6) and uv spectral shifts during oxidation of IAA were reported by Meudt (3). The present paper reports a new procedure for the assay of horseradish peroxidase catalyzed oxidation of IAA. The assay procedure is based on the continuous measurement of a fluorescent product of the reaction.