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Related Concept Videos

Reaction Mechanisms: The Steady-State Approximation01:26

Reaction Mechanisms: The Steady-State Approximation

The steady-state approximation, also referred to as the quasi-steady-state approximation to differentiate it from a true steady state, is a widely used method for simplifying calculations in complex reaction mechanisms. This approach is particularly useful when dealing with multi-step reactions that involve reverse reactions or several steps, which can significantly increase mathematical complexity and make the reactions nearly unsolvable analytically.The steady-state approximation operates on...
Reaction Mechanisms: Rate-limiting Step Approximation01:29

Reaction Mechanisms: Rate-limiting Step Approximation

The rate-determining step, or RDS, in a chemical reaction is the slowest step that determines the overall reaction rate. It is identified by using the observed rate law and typically involves approximation methods like the RDS approximation or the steady-state approximation.In the RDS approximation, also known as the rate-limiting-step or equilibrium approximation, the reaction mechanism consists of one or more reversible reactions near equilibrium, followed by a slower RDS, and then one or...
Introduction to Enzyme Kinetics01:19

Introduction to Enzyme Kinetics

Enzyme kinetics studies the rates of biochemical reactions. Scientists monitor the reaction rates for a particular enzymatic reaction at various substrate concentrations. Additional trials with inhibitors or other molecules that affect the reaction rate may also be performed.
The experimenter can then plot the initial reaction rate or velocity (Vo) of a given trial against the substrate concentration ([S]) to obtain a graph of the reaction properties. For many enzymatic reactions involving a...
Enzyme Kinetics01:19

Enzyme Kinetics

Enzymes speed up reactions by lowering the activation energy of the reactants. The speed at which the enzyme turns reactants into products is called the rate of reaction. Several factors impact the rate of reaction, including the number of available reactants. Enzyme kinetics is the study of how an enzyme changes the rate of a reaction.
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Multi-Step Reactions02:31

Multi-Step Reactions

Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...
Transition State Theory01:25

Transition State Theory

Transition-state theory, also known as activated-complex theory, provides a molecular-level explanation of reaction rates in both gas-phase and solution-phase reactions. It extends earlier kinetic models by considering the formation of a short-lived, high-energy configuration during a reaction.The progress of a chemical reaction can be represented using a reaction profile, which plots potential energy against the reaction coordinate. As two reactant molecules approach one another, their...

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Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
09:42

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes

Published on: January 16, 2016

Reactant stationary approximation in enzyme kinetics.

Sonya M Hanson1, Santiago Schnell

  • 1Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089-0484, USA.

The Journal of Physical Chemistry. A
|August 22, 2008
PubMed
Summary
This summary is machine-generated.

The reactant stationary approximation is not always sufficient for the quasi-steady-state approximation in enzyme kinetics. This study clarifies these approximations for accurate reaction parameter determination.

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Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions
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Area of Science:

  • Biochemistry
  • Chemical Kinetics
  • Enzyme Kinetics

Background:

  • The quasi-steady-state approximation (QSSA) is widely used in enzyme kinetics.
  • It typically assumes an initial transient phase where substrate concentration is constant.
  • This assumption is termed the reactant stationary approximation.

Purpose of the Study:

  • To investigate the relationship between the reactant stationary approximation and the quasi-steady-state approximation.
  • To analyze the dynamic behavior of single enzyme-single substrate reactions with endogenous substrates.
  • To clarify the conditions under which the QSSA is valid.

Main Methods:

  • Mathematical modeling of enzyme kinetics.
  • Analysis of dynamic reaction behavior.
  • Comparison of reactant stationary and quasi-steady-state approximations.

Main Results:

  • The reactant stationary approximation and the QSSA are shown to be distinct approximations.
  • The reactant stationary approximation is not always a sufficient condition for applying the QSSA.
  • Dynamic analysis reveals conditions where these approximations diverge.

Conclusions:

  • Enzyme kinetic parameter determination requires careful consideration of both approximations.
  • The validity of the QSSA depends on factors beyond just substrate concentration remaining constant.
  • This research provides a more nuanced understanding for accurate modeling of enzyme-catalyzed reactions.