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Mapping the transition state for ATP hydrolysis: implications for enzymatic catalysis
1B400 Beckman Center, Department of Biochemistry, Stanford University, CA 94305-5307, USA.
Chemistry & Biology
|November 1, 1995
Summary
Uncatalyzed phosphoryl transfer from adenosine triphosphate (ATP) proceeds through a dissociative transition state, with minimal nucleophile interaction and significant bond cleavage. This finding clarifies enzyme-catalyzed phosphoryl transfer mechanisms.
Area of Science:
- Biochemistry
- Chemical Kinetics
Background:
- Phosphoryl transfer reactions, often using adenosine triphosphate (ATP) as a high-energy phosphate donor, are fundamental in biological processes.
- The transition state for phosphoryl transfer from ATP in solution has remained largely uncharacterized.
- Studying uncatalyzed ATP hydrolysis provides a baseline for understanding enzyme-catalyzed reactions.
Purpose of the Study:
- To systematically investigate the transition state for phosphoryl transfer from ATP in solution.
- To provide a foundational understanding for dissecting enzyme-catalyzed phosphoryl transfer mechanisms.
Main Methods:
- Examined phosphoryl transfer reactions involving ATP, GTP, and pyrophosphate with various alcohols.
- Analyzed Brønsted beta(nucleophile) and beta(leaving group) values to characterize transition state structures.
- Assessed the effect of magnesium ion (Mg2+) coordination on the transition state.
Main Results:
- A small Brønsted beta(nucleophile) value (0.07) indicates minimal bond formation between the nucleophile and the phosphoryl group in the transition state.
- A large, negative Brønsted beta(leaving group) value (-1.1) suggests significant cleavage of the bond between phosphorus and the leaving group oxygen.
- Coordination of Mg2+ did not measurably alter the Brønsted beta(nucleophile) value.
Conclusions:
- Uncatalyzed ATP hydrolysis in solution exhibits a dissociative, metaphosphate-like transition state.
- The transition state involves limited nucleophile-ATP bond formation and substantial breaking of the bond to the ADP leaving group.
- Bound Mg2+ does not alter the dissociative nature of the transition state, supporting its role in facilitating phosphoryl transfer through a dissociative mechanism.