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Turnover Number and Catalytic Efficiency

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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.
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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.

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Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions

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Published on: April 4, 2014

Catalytic efficiency and kcat/KM: a useful comparator?

Robert Eisenthal¹, Michael J Danson, David W Hough

¹Department of Biology & Biochemistry, University of Bath, Bath, UK.

Trends in Biotechnology

|April 17, 2007

Summary

The specificity constant (k(cat)/K(M)) is useful for comparing enzyme activity on different substrates. However, using it to compare enzyme effectiveness on the same substrate can be misleading and requires careful consideration.

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Published on: August 19, 2013

Area of Science:

Biochemistry
Enzymology
Molecular Biology

Background:

The specificity constant (k(cat)/K(M)) is a key metric in enzymology.
It is commonly used to assess an enzyme's preference for different substrates.
Misapplication of this constant can lead to inaccurate conclusions.

Purpose of the Study:

To clarify the appropriate use of the specificity constant (k(cat)/K(M)).
To highlight the limitations of using k(cat)/K(M) for comparing enzyme catalytic efficiency.
To provide guidance on interpreting enzyme kinetics data.

Main Methods:

Review of established kinetic principles.
Analysis of common misinterpretations of enzyme kinetic data.
Theoretical discussion of enzyme efficiency metrics.

Main Results:

The specificity constant (k(cat)/K(M)) accurately reflects relative substrate discrimination.
Using k(cat)/K(M) to compare the catalytic efficiency of different enzymes on the same substrate is problematic.
Alternative interpretations are necessary when comparing enzyme performance.

Conclusions:

The specificity constant (k(cat)/K(M)) should be used cautiously when comparing enzyme effectiveness across different enzymes.
Clear distinction between substrate specificity and catalytic efficiency is crucial.
Accurate interpretation of enzyme kinetics is vital for reliable biochemical research.