Microbial synthesis and degradation of indole-3-acetic acid. I. The conversion of L-tryptophan to indole-3-acetamide by an enzyme system from Pseudomonas savastanoi.

An enzyme which catalyzes the conversion of L-tryptophan to indole-3-acetamide has been isolated from cells of Pseudomonas savastanoi and purified 89-fold. The enzyme catalyzes a reaction in which 1 mole of L-tryptophan and 1 mole of 02 are consumed and 1 mole of indole-3-acetamide and 1 mole of CO2 are produced. The enzyme has a pH optimum between 7.2 and 9.2. It is specific for the L isomer of tryptophan and attacks 5-hydroxytryptophan at a rate approximately 17% of that for L-tryptophan. It shows slight activity toward L-phenylalanine and L-tyrosine but no activity toward indole-3-pyruvic acid, indole-3-acetaldehyde, amethyltryptophan, or indole-3-acetic acid. Indole-3-acetamide brings about end product inhibition and, at a concentration of 1 mM, reduces the rate of oxidation of L-tryptophan by 85 %. Hydroxylamine, HgCI 2, iodoacetamide, and indole3-acetic acid are effective inhibitors of the enzyme. Tryptophan oxidative decarboxylase is suggested for the trivial name for this enzyme.