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Related Concept Videos

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.
Scientists typically study enzyme kinetics with a fixed amount of enzyme in the controlled environment of a test tube. When more reactant, or substrate, is...
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...
Turnover Number and Catalytic Efficiency01:19

Turnover Number and Catalytic Efficiency

The turnover number of an enzyme is the maximum number of substrate molecules it can transform per unit time. Turnover numbers for most enzymes range from 1 to 1000 molecules per second. Catalase has the known highest turnover number, capable of converting up to 2.8×106 molecules of hydrogen peroxide into water and oxygen per second. Lysozyme has the lowest known turnover number of half a molecule per second.
Chymotrypsin is a pancreatic enzyme that breaks down proteins during digestion. The...
Catalytically Perfect Enzymes01:07

Catalytically Perfect Enzymes

The theory of catalytically perfect enzymes was first proposed by W.J. Albery and J. R. Knowles in 1976. These enzymes catalyze biochemical reactions at high-speed. Their catalytic efficiency values range from 108-109 M-1s-1. These enzymes are also called 'diffusion-controlled' as the only rate-limiting step in the catalysis is that of the substrate diffusion into the active site. Examples include triose phosphate isomerase, fumarase, and superoxide dismutase.
Quantitative Aspects of Drug-Receptor Interaction01:30

Quantitative Aspects of Drug-Receptor Interaction

The receptor occupancy theory connects a drug's response to the number of occupied receptors. With higher drug concentrations, more receptors are occupied, leading to increased responses. The formation of drug-receptor complexes involves association and dissociation rates, which reach equilibrium when the forward and backward reactions are equal. The equilibrium association constant (Ka) and its inverse, the equilibrium dissociation constant (Kd), indicate drug affinity. Higher Ka and lower Kd...

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Related Experiment Video

Updated: Jul 9, 2026

Defining Substrate Specificities for Lipase and Phospholipase Candidates
08:59

Defining Substrate Specificities for Lipase and Phospholipase Candidates

Published on: November 23, 2016

A quantitative index of substrate promiscuity.

Abhinav Nath1, William M Atkins

  • 1Department of Medicinal Chemistry, Box 357610, University of Washington, Seattle, Washington 91895-7610, USA.

Biochemistry
|December 18, 2007
PubMed
Summary

Enzymes can perform multiple reactions, a trait called catalytic promiscuity. This study introduces a new quantitative index to measure enzyme promiscuity, aiding in understanding enzyme evolution and engineering.

Area of Science:

  • Biochemistry
  • Enzymology
  • Molecular Biology

Background:

  • Catalytic promiscuity, the ability of enzymes to catalyze multiple reactions, is crucial for enzyme evolution and drug metabolism.
  • Currently, there is no quantitative method to measure or compare enzyme promiscuity.
  • Understanding promiscuity is vital for biocatalyst engineering and drug development.

Purpose of the Study:

  • To develop a quantitative index for measuring enzyme promiscuity.
  • To establish a method for comparing promiscuity across different enzyme classes.
  • To investigate the relationship between substrate promiscuity and enzyme activity.

Main Methods:

  • Defined a quantitative index of promiscuity (I) based on catalytic efficiencies against a set of substrates.

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Real Time Measurements of Membrane Protein:Receptor Interactions Using Surface Plasmon Resonance (SPR)
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  • Developed a weighted promiscuity index (J) considering substrate similarity.
  • Calculated promiscuity indices for serine/cysteine proteases, glutathione S-transferases (GSTs), and cytochrome P450s (CYPs).

    • Main Results:

    • Promiscuity indices varied widely among proteases, from 0.00 (granzyme B) to 0.83 (cruzain).
    • Drug-metabolizing enzymes (GST A1-1, CYPs) showed high promiscuity (J values 0.72–0.92).
    • GST A4-4 exhibited moderate promiscuity (J = 0.37), while others were highly promiscuous.

    Conclusions:

    • The developed indices provide a quantitative measure for enzyme promiscuity.
    • This quantitative approach enables comparisons across enzyme classes and aids in understanding enzyme function.
    • The study highlights the high promiscuity of drug-metabolizing enzymes and offers insights for enzyme engineering.