Tryptophanase bacterial

Test for indole Indole is a component of the amino acid tryptophan, which can he broken down by the bacterial enzyme tryptophanase. When tryptophan is broken down, the presence of indole can be detected through the use of Kovacs reagent. Kovacs reagent, which is yellow, reacts with indole and produces a red colour on the surface of the test tube. Kovacs reagent is prepared by dissolving 10 g of p-aminobenzaldehyde in 150 mL of isoamylalcohol and then slowly adding 50 mL of concentrated HCl. 

The closely related bacterial enzyme tyrosine phenol-lyase [137] has an even wider substrate and reaction specificity than tryptophanase, including the remarkable ability to cleave both D- and L-tyrosine and to interconvert D- and L-alanine. As already discussed and summarized in Tables 1 and 2, the stereochemistry at C-/J in all the a,/3-elimination and -replacement reactions of this enzyme studied so far is always retention [108,109,129]. This includes the a, -elimination of L- as well as of D-tyrosine. The fate of the a-hydrogen of L-tyrosine in this reaction has been probed in preliminary experiments (H. Kumagai, E. Schleicher and H.G. Floss, unpublished results), and the results tentatively suggest transfer of deuterium from the a-position to C-4 of the resulting phenol. Attempts to demonstrate intramolecularity of this transfer have so far been inconclusive. The base abstracting H-a in this enzyme may be histidine [138]. 

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