New tryptophanase inhibitors: Towards prevention of bacterial biofilm formation

Figures & data

Scheme 1.  The enzymatic reaction of Tnase with tryptophan results in pyruvate, ammonia and indole production [8].

Scheme 2.  The α,β-elimination reaction of SOPC results in the production of o-nitrothiophenolate, pyruvate and ammonia.

Figure 1.  Michaelis-Menten plot of Tnase with S-phenyl-benzoquinone tryptophan. SOPC at different concentrations was used as a substrate, as described in the experimental section. Analyses were done with Calidagraph version 4. Measurements were performed in the absence, ○, and the presence of the inhibitor at a concentration of 47.5 μM, ◊; 95 μM, ▪; 190 μM, X.

Table I.  Kinetics parameters of the Tnase inhibitors.

Inhibitor	Ki (mM)	Suggested type of inhibition	Structure
N-acetyl tryptophan	48 ± 3	noncompetitive
L-tryptophan-ethylester (p-toluene sulfuric acid salt)	52 ± 0.1	competitive
S-phenylbenzoquinone tryptophan	101 ± 2	uncompetitive
α-Amino-2-(9,10-anthraquinone)-popanoic acid	174 ± 9	noncompetitive

Figure 2.  Michaelis-Menten plot of Tnase with N-acetyl-tryptophan. SOPC was used as a substrate at different concentrations. Measurements were performed in the absence, ○, and the presence of the inhibitor at a concentration of 15.5 μM, ◊; 31 μM, ▪; 62 μM, X.

Figure 3.  Michaelis-Menten plot of Tnase with p-Toluene sulfonic acid salt of L-tryptophan-ethylester. SOPC was used as a substrate at different concentrations. Measurements were performed in the absence, ○, and the presence of the inhibitor at a concentration of 26 μM, ◊; 52 μM, ▪.

Figure 4.  Michaelis-Menten plot of Tnase with α-Amino-2-(9,10-anthraquinone)-propanoic acid. SOPC was used as a substrate at different concentrations. Measurements were performed in the absence, ○, and the presence of the inhibitor at a concentration of 55 μM, ◊; 110 μM, ▪; 220 μM, X.

Scheme 3.  The mechanism of catalysis of Tnase as proposed by Snell & Mari [21].

WA Newton, and EE Snell. (1962). An inducible tryptophan synthase in tryptophan auxotrophs of Escherichia coli. Proc Natl Acad Sci USA 48:1431–1439.

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EE Snell, and SJ Mari. Schiff base intermediates in enzyme catalysis. In: PD Boyer. editor. The Enzymes., vol. 2 (1970) p 335–370.

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