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The mechanism of indoleglycerol phosphate synthesis from indole and D-glyceraldehyde 3-phosphate catalyzed by tryptophan synthase has been investigated by steady-state kinetic techniques. The equilibrium constant and the progress curves were measured by use of the difference in absorbance between indole and indoleglycerol phosphate. Stopped-flow measurements show that only the non-hydrated form of D-glyceraldehyde 3-phosphate serves as substrate. The product analogue indolepropanol phosphate was used as an inhibitor to discriminate between possible mechanisms. The data agree well with an ordered addition mechanism with D-glyceraldehyde 3-phosphate adding first. Mechanisms involving random addition of substrates or ordered addition with indole adding first can be excluded because indolepropanol phosphate is a competitive inhibitor only towards glyceraldehyde 3-phosphate. The high affinity of tryptophan synthase for indoleglycerol phosphate leads to product inhibition even at small extents of reaction. Glyceraldehyde 3-phosphate combines with the enzyme with an apparent second-order rate constant, which is not diffusion controlled and generates a site with high affinity for indole.
W O Weischet, and
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January 1987,
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W O Weischet, and
K Kirschner
January 1991,
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W O Weischet, and
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February 1978,
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W O Weischet, and
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W O Weischet, and
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May 1998,
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W O Weischet, and
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W O Weischet, and
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March 1970,
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W O Weischet, and
K Kirschner
March 1989,
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W O Weischet, and
K Kirschner
August 1993,
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W O Weischet, and
K Kirschner
February 1995,
Bioorganic & medicinal chemistry,
