Enzymatic Formation of Indole-3-Carboxaldehyde from Indole-3-Acetic Acid.

Abstract

It was first suggested by Tang and Bonner (14) that indole-3-carboxaldehyde is the product of the oxidative degradation of indole-3-acetic acid (IAA) by crude enzyme preparations from etiolated pea seedlings. Using the more active bean root enzyme, Wagenknecht and Burris (15) attempted without success to obtain the 2,4-dinitrophenylhydrazone of the aldehyde. On the basis of chromatographic data, Racusen (9) reports that the pea enzyme forms small amounts of the aldehyde. More recently, Wagenknecht (personal communication) has made similar observations with the bean root system. Ray and Thimann (10) and Ray (11) have recently reported that the enzyme from Omphalia fiavida is unable to form the aldehyde. The recent work of Maclachlan and Waygood (6) likewise has left unsettled the nature of the end product. Manning and Galston (7) have reported the formation in the pea system of two products having high Rf values and giving qualitative color tests which indicate a similarity to our products # 4 and #5 (see below). They were unable to demonstrate the formation of indole-3-carboxaldehyde, and also ruled out orifto-formamidoacetophenone, ori/io-aminoacetophenone, and 4-hydroxyquinoline as major end products, although they believe that the indole ring is ruptured. Chromatographic separation and spectrophotometric examination of the products of the IAA oxidase-peroxidase system from Lupinus albus L. (13) gave no indication that the aldehyde was formed; likewise, the results obtained when the chromatograms were tested with 2,4-dinitrophenylhydrazine hydrochloride, modified Salkowski (3), and Ehrlich reagent suggested the absence of the aldehyde. In view of the conflicting results, attempts were made to suplement the purified IAA oxidase with the auxiliary enzyme systems presumed to be present in the crude enzyme preparations employed in the early investigations. The present report is concerned with the coupling of the oxidase system to the cytochrome oxidase system. Under these conditions the formation of indole-3-carboxaldehyde as a major reaction product was observed.