You are constructing a velocity versus [substrate] curve for...

You are constructing a velocity versus [substrate] curve for an enzyme whose $K_{M}$ is believed to be about $2 \mu$ M. The enzyme concentration is $200 \mathrm{nM}$ and the substrate concentrations range from $0.1 \mu \mathrm{M}$ to $10 \mu \mathrm{M}$ What is wrong with this experimental setup and how could you fix it?

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Key Concepts

Michaelis-Menten Kinetics

Michaelis-Menten kinetics is the framework for analyzing enzyme-catalyzed reactions. It involves measuring the initial velocity by varying substrate concentration while keeping the enzyme concentration low relative to the substrate. The kinetic parameters, including KM, are accurately determined only when the substrate is in vast excess, ensuring that the enzyme operates under steady-state conditions without significant substrate depletion.

Importance of Maintaining Excess Substrate over Enzyme

A key requirement in enzyme kinetics experiments is that the substrate concentration must be much higher than the enzyme concentration. This ensures that the binding of enzyme to substrate does not significantly deplete the available substrate, which is critical for accurately determining kinetic parameters like KM. Inadequate substrate excess leads to nonsteady state conditions, potential substrate depletion, and unreliable kinetic measurements. Adjusting the enzyme concentration downwards or increasing the substrate concentration range would correct this issue.

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