Enzyme kinetics determined using calorimetry: a general assay for enzyme activity?

Area of Science:

• Biochemistry
• Enzymology
• Biophysical Chemistry

Background:

• Enzyme kinetics are crucial for understanding biological processes.
• Traditional methods for enzyme kinetic analysis can be complex and time-consuming.
• Isothermal titration microcalorimetry (ITC) offers a sensitive, label-free approach to study biochemical reactions.

Purpose of the Study:

• To present two novel techniques for determining enzyme kinetic constants using ITC.
• To demonstrate the versatility and precision of these methods for enzyme characterization.
• To showcase the applicability of ITC for measuring enzyme inhibition.

Main Methods:

• Developed two ITC-based methods: substrate titration under pseudo-first-order conditions and continuous monitoring of thermal power during substrate depletion.
• Applied these methods to enzymes representing all six EC classifications.
• Utilized physiological substrates and analyzed reactions in spectroscopically opaque solutions.

Main Results:

• Achieved highly precise kinetic characterization of enzymes in a single experiment.
• Successfully measured enzyme inhibition using the developed ITC techniques.
• Demonstrated broad applicability across oxidation-reduction, transferase, hydrolytic, lyase, and ligase enzyme activities.

Conclusions:

• The presented ITC methods provide a universal, precise, and non-destructive approach for enzyme kinetic analysis.
• These techniques are suitable for a wide range of enzymes, including those in challenging sample matrices.
• The universal assay holds significant potential for functional genomics and drug discovery.