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[Steady state kinetics of pyruvate kinase from muscle]
Abstract:
The dependence of the forward pyruvate kinase reaction on the concentrations of ADP and Mg2+ was studied. It was shown that high total ADP concentrations (2-15 mM) exceeding total Mg2+ concentration in the medium lead to the inhibition of the pyruvate kinase reaction, whereas relatively high Mg2+ concentrations (up to 15 mM) do not cause any inhibition. The kinetics of the reaction can be described in the best way by a scheme incorporating the active PEP . E . Mg2+ . Mg . ADP complex and dead-end complexes containing free ADP. An analysis of the experimental data allows to determine all coefficients of the rate equation and to calculate the values of all kinetic parameters. The values of the constants obtained were used for mathematical simulation of the reaction on the basis of the kinetic scheme given. The mathematical model obtained describes satisfactorily the experimentally determined dependences, which is indicative of the correctness of the model.
Insights
High concentrations of ADP inhibit the pyruvate kinase reaction, but Mg2+ does not. A kinetic model incorporating active and dead-end complexes accurately describes these findings.
Area of Science:
- Biochemistry
- Enzyme kinetics
Context:
- Pyruvate kinase (PK) is a key enzyme in glycolysis.
- Understanding PK regulation is crucial for metabolic studies.
Purpose:
- To investigate the influence of ADP and Mg2+ concentrations on forward pyruvate kinase reaction rates.
- To develop and validate a kinetic model for PK activity.
Summary:
- The study demonstrates that elevated ADP levels (2-15 mM), exceeding Mg2+ concentrations, inhibit pyruvate kinase.
- Conversely, high Mg2+ concentrations (up to 15 mM) did not inhibit the enzyme.
- A kinetic model, including active PEP.E.Mg2+.Mg.ADP complexes and dead-end ADP complexes, accurately describes the observed kinetics.
- All rate equation coefficients and kinetic parameters were determined, enabling successful mathematical simulation.
Impact:
- Provides a validated kinetic model for pyruvate kinase.
- Offers insights into enzyme regulation by substrate and cofactor concentrations.
- Contributes to a deeper understanding of glycolytic pathway control.