OXIDATION OF INDOLEACETIC ACID BY A HOMOGENEOUS TOMATO FRUIT PEROXIDASE

Abstract

A purified, homogeneous tomato fruit peroxidase was used to study the oxidation of indoleacetic acid (IAA) in the presence of a phenolic compound and managanese. The reaction was completely inhibited by potassium cyanide and sodium meta-bisulfite when these compounds were added initially. However, when these compounds were added after the reaction had begun, potassium cyanide did not completely inhibit whereas sodium meta-bisulfite did. Also, the ultraviolet spectrum of the reaction products indicated that methyleneoxindole was the primary product. Several monophenols were capable of serving as cofactors, but o-dihydroxyphenols were inhibitors of IAA oxidation by tomato peroxidase. The inhibition was characterized by an extension of the induction period after which oxidation proceeded as normal. These results suggest that IAA oxidation by tomato fruit peroxidase proceeds autocatalytically via a free radical mechanism and that o-dihy-droxyphenols could be serving as chain-stopping agents. The changes in the phenolic pool during fruit development could affect IAA oxidation and be related to the fruit ripening process.