Tryptophan indole-lyase

This enzyme [EC 4.1.99.1], also known as L-tryptophan indole-lyase, catalyzes the hydrolysis of L-tryptophan to generate indole, pyruvate, and ammonia. The reaction requires pyridoxal phosphate and potassium ions. The enzyme can also catalyze the synthesis of tryptophan from indole and serine as well as catalyze 2,3-elimination and j8-replacement reactions of some indole-substituted tryptophan analogs of L-cysteine, L-serine, and other 3-substituted amino acids. 

Iyase, ° cystathione y-Iyase, and tryptophan indole lyase are particularly... 

Absorption bands at 500 nm. With many PLP enzymes certain substrates and inhibitors cause the appearance of intense and unusually narrow bands at 500 nm. Such a band is observed with aspartate aminotransferases acting on eryf/zro-3-hydroxyaspartate (Fig. 14-9). This substrate undergoes transamination very slowly, and the 500-nm absorbing form which accumulates is probably an intermediate in the normal reaction sequence. A similar spectrum is produced by tryptophan indole-lyase acting on the competitive inhibitor L-alanine. Under the same conditions the... 

Tryptophanase (L-tryptophan indole-lyase (deaminating) EC 4.1.99.1) belongs to the family of the pyridoxal 5 -phosphate (PLP)-dependent enzymes. It serves in vivo to degrade L-tryptophan, is induced by L-tryptophan, and found in various bacteria, particularly in enteric species. Tryptophanase catalyzes a,/3-elimination1 and /3-replacement reactions on interaction with L-tryptophan and various other /3-substituted amino acids2 ... 

D- and L- Serine dehydratases (deaminases) Tryptophan indole-lyase (tryptophanase) Tyrosine phenol-lyase ... 

The approaches that have been described in some detail for tryptophan synthase may be applied to other PLP-dependent enzymes. Tryptophan indole lyase, or tryptophanase, catalyzes the PLP-dependent P-elimination of indole from tryptophan to yield indole, pyruvate, and NH4+ (Equation 4). 

Fig. 16. Rapid-scanning data for the reactions of 5 mM indole (A) and 5 mM benzimidazole (B) with 17.2 iM tryptophan indole-lyase (tryptophanase) that has been preequilibrated with 0.25mM t-alanine. i-Alanine was premixed in both syringes to prevent unwanted concentration changes. In panel A, scans were collected at 15,92.5,170,247.5, 325,402.5,480,557.5, 635, 712.5, 790,867.5, and 945 ms after flow stopped. Spectrum 0 represents the spectrum of the enzyme-alanine complex before mixing with indole. In panel B, scans were collected at 15, 390, 765, 1140, 1515, 1890, 2265,2640, 3015,3390, 3765, and 4140 ms after mixing. Spectrum 0 represents the enzyme-alanine complex before mixing with benzimidazole. [Taken from Phillips (104) with permission.]...

Indole protonation is a functional step in the cleavage of tryptophan by tryptophan indole-lyase, based on kinetic isotope effect measurements [26]. 

Tryptophan synthase (TS) catalyzes the ultimate step in tryptophan biosynthesis (details see Fig. 4.2). Indole and benzoxazinoid secondary metabolite formation branches from this pathway. The two lyases IGL and BXl cleave indole-3-glycerol phosphate into indole (and glycerolaldehyde-3-phosphate, not shown) and serve as committing enzymes for indole derived secondary metabolites. Indole produced by IGL directly functions as volatile signal. Indole produced by BXl is converted by other enzymes (BX2-BX9) to benzoxazinoids that have an important function in the chemical defense of grasses. 

Figure 4.2 Functional comparison of the indole-3-glycerole phosphate lyases IGL and BXI with the tryptophan synthase complex.

L-Tryptophan synthase, tryptophan desmolase, L-serine hydro-lyase (adding imhleglycerol-phos-phate) (EC 4.2.1.20) the enzyme catalysing the synthesis of L-tryptophan from L-serine and indole 3-glycerol phosphate. T.s. from E. coli (M, 149,000) and other prokaryotes has 02 subunit composition. The enzyme separates easily into monomeric subunit a (also called protein B, M, 29,000) and dimeric subunit 02 (also called protein B Af, of dimer 90,000) when eluted from DEAE cellulose with a sodium chloride gradient. The separated subunits catalyse partial reactions of L-tryptophan synthesis ... 

The fifth enzyme activity, tryptophan synthetase [EC 4.2.1.20, L-serine hydro-lyase (adding indole)], catalyzes the final step in tryptophan synthesis. It consists of a complex of two nonidentical protein subunits, B (/ -chains) and A (a-chains) [7,14,38-41], which are coded for by the fourth and fifth tryptophan genes, respectively, in E. coli [14] and S. typhimurium [27]. The A subunit has been purified and shown to be a single polypeptide a-chain [42]. Wilson and Crawford [39] purified the B-protein subunit. Their conclusion that it was a dimer P2) which complexed with two a-chain subunits to form the tryptophan synthetase ( 2 Pi) is supported by other studies of the subunits and their association [40,41], The two proteins of tryptophan synthetase (TS) can catalyze the following reactions [38,43]. 

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