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How thiamine diphosphate is activated in enzymes
1Institut für Biochemie, Martin-Luther Universität Halle-Wittenberg, Kurt-Mothes-Strasse 3, D-06120 Halle, Germany.
Science (New York, N.Y.)
|January 3, 1997
Summary
The enzyme mechanism for activating thiamine diphosphate (vitamin B1) involves a glutamate residue activating the 4'-amino group. This accelerates proton removal from the C2 atom, excluding prior proposed mechanisms.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Thiamine diphosphate (vitamin B1) is crucial for various metabolic enzymes.
- Understanding thiamine diphosphate activation is key to enzyme mechanism elucidation.
Purpose of the Study:
- To investigate the activation mechanism of thiamine diphosphate in pyruvate decarboxylase and transketolase.
- To determine the role of protein interactions in coenzyme activation.
Main Methods:
- Nuclear magnetic resonance (NMR) spectroscopy
- Proton/deuterium exchange studies
- Coenzyme analogs and site-specific mutant enzymes
Main Results:
- A glutamate residue interacts with the pyrimidine ring, activating the 4"-amino group.
- The enzyme significantly accelerates C2 proton deprotonation, orders of magnitude faster than the overall reaction.
- This finding excludes concerted mechanisms or C2 carbanion stabilization.
Conclusions:
- The study clarifies the thiamine diphosphate activation mechanism in key enzymes.
- Protein-mediated proton transfer is critical for coenzyme function.
- Proposed mechanisms involving concerted reactions or carbanion stabilization are refuted.