A graphical method for extracting rate constants from some enzyme-catalyzed reactions not monitored to completion

Area of Science:

• Biochemistry
• Enzymology
• Chemical Kinetics

Background:

• Enzyme-catalyzed reactions often follow complex kinetic models.
• Traditional methods for determining rate constants (k) from absorbance-time data are time-consuming, requiring 10-15 half-lives.

Purpose of the Study:

• To develop a more efficient graphical method for determining the rate constant (k) in enzyme kinetics.
• To reduce the experimental time required for kinetic analysis of enzyme-catalyzed reactions.

Main Methods:

• A novel graphical method plotting (y'' - y') vs. (y' - y0) was developed.
• This method utilizes product formation data (y) at sequential time points (t, t + Δt, t + 2Δt).
• The rate constant (k) is extracted from the slope of this plot.

Main Results:

• The new graphical method accurately determines the rate constant (k).
• This method requires monitoring the reaction for only three to five half-lives of the exponential phase.
• The method was successfully applied to measure the activation rate of a papain mixed disulfide.

Conclusions:

• A simplified and rapid graphical method for determining enzyme reaction rate constants (k) has been established.
• This technique significantly reduces the time needed for kinetic studies.
• The method offers a reliable alternative for analyzing enzyme kinetics, particularly for reactions with slow phases.