Metabolism of Indole‐3‐acetaldehyde

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Abstract
Infiltration of indolcacelaldehyde (IAAId) into living tissues of sonic lower and higher plants gives rise simultaneously to both indoleacetic acid (IAA) and Iryptophol (T‐ol). But on a molar basis, there is no correlation between the products indicating a disimitation. Expressed juice of Avena coleoptiles by itself, exhibits only IAA forming activity. Approximately two moles of IAAld are consumed for each mole of IAA formed at pH 4.5, but only if necessary corrections are made for losses of substrate and products. Addition of reduced NAD or NADP readily induces tryptophol formation. But even at pH 4.5, adding reduced NADP causes greater tryptophol formation, leading to a marked divergence in the acid‐alcohol ratio. Varying the pH in the presence of reduced coenzymes also alters the ratio, with alcohol formation predominating. NAD and NADP have no influence on the formation of IAA from IAAld by the whole cytoplasm of Avena coleoptiles. Whole cytoplasm of Asparagus shoots forms both IAA and tryptophol from IAAld, but in widely varying amounts, devoid of any suggestive stoichiometry between the products.With the acetone powder of Avena coleoptiles including the first leaf, data indicating an apparent disimitation of IAAld are obtainable only at pH 4.5. On altering the pH however, unequal amounts of the two products, namely IAA and tryptophol, are formed and hence a different ratio results. Acetone powders of wheat coleoptiles and Asparagus shoots do not yield data supporting disimitation either at pH 4.5 or 7.2.IAA formation in Avena is aerobic while tryptophol formation is seemingly independent of oxygen supply. The former activity is selectively abolished by 10−3M dithionite while the latter activity suffers a similar suppression in the presence of 10−3M manganese sulphate. Varying the IAAld concentration results in unequal amounts of the two products, revealing the dissimilar affinity of the two activities for the common substrateSaturation to a level of 30 percent with ammonium sulphate throws out most of the acid‐forming activity whereas the alcohol‐forming system appears mostly in the protein fraction precipitated between 30 and 40 percent saturation. The enzyme system of Avena coleoptiles oxidizing IAAld to IAA can also be easily separated by Sephadex gel filtration and its independent activity demonstrated in the total absence of tryptophol formation.Based on the heterogeneous properties of the two activities, metabolism of IAAld in Avena coleoptiles is believed to be mediated by two independent enzyme systems without the intervention of a mutase or a dismutation mechanism.