Microbial Synthesis and Degradation of Indole-3-acetic Acid

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 CO 2 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 indole-3-acetic acid are effective inhibitors of the enzyme.Tryptophan oxidative decarboxylase is suggested for the trivial name for this enzyme.