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Kinetics and mechanism in RNA cleavage
1Department of Chemistry, Columbia University, New York, NY 10027-6948.
Summary
Imidazole buffers catalyze RNA cleavage via a sequential bifunctional mechanism. A two-step process involves substrate conversion to a phosphorane intermediate, followed by cleavage product formation.
Area of Science:
- Biochemistry
- Chemical Kinetics
- Molecular Biology
Background:
- RNA cleavage is fundamental to various biological processes.
- Understanding the catalytic mechanisms of RNA degradation is crucial.
- Imidazole buffers serve as model systems for studying RNA catalysis.
Purpose of the Study:
- To elucidate the sequential bifunctional mechanism of RNA cleavage catalyzed by imidazole buffers.
- To determine kinetic parameters and identify all plausible reaction mechanisms.
- To relate these findings to the enzymatic action of ribonuclease.
Main Methods:
- Experimental studies on the cleavage of poly(U), 3',5''-UpU, 2',5''-UpU, and 3',5''-ApA.
- Detailed steady-state kinetic analysis.
- Consideration of experimental evidence for accompanying isomerization reactions.
Main Results:
- A sequential bifunctional catalytic mechanism was identified.
- The mechanism involves a two-step process: substrate to phosphorane intermediate, then phosphorane to products.
- All viable mechanisms involve the second catalyst acting on a phosphorane monoanion.
Conclusions:
- The catalytic mechanism involves a phosphorane monoanion intermediate.
- This intermediate can form directly or via proton equilibrations.
- The findings provide insights into the potential mechanism of ribonuclease action.