AI Article Synopsis
- The study investigates how indoleglycerol phosphate is synthesized from indole and D-glyceraldehyde 3-phosphate through the enzyme tryptophan synthase using steady-state kinetic methods.
- It reveals that only the non-hydrated form of D-glyceraldehyde 3-phosphate is used as a substrate and supports an ordered mechanism where D-glyceraldehyde 3-phosphate is added first.
- The findings also show that indolepropanol phosphate acts as a competitive inhibitor, reinforcing the ordered mechanism and indicating high product inhibition due to the enzyme’s strong affinity for indoleglycerol phosphate.
Article Abstract
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.
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| http://dx.doi.org/10.1111/j.1432-1033.1976.tb10350.x | DOI Listing |
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