I am adding an inhibitor to the enzyme. The Vmax decreased with increase of inhibitor concentration.The mechanism found out, showed a "mixed type of enzyme-inhibition". It was hypothesized that activation energies (10, 20, 30, 40 oC) should increase with inhibition of enzyme (decrease in Vmax). But I found that activation energies decreased with the inhibition of an enzyme.
Hi there,
Energy of activation for a given catalyzed reaction is not actually variable. At a given enzyme concentration what does vary according to different parameters (temperature, substrate concentration, presence of inhibitor) is the apparent velocity of the reaction (ie apparent velocity constant k) which is mainly dependent on the probability of efficient collision between substrate and enzyme. k is increased when temperature increases (because there are more collisions) and k is decreased as inhibitor concentration is increased (because fraction of unproductive collisions between enzyme and inhibitor increases).
True: activation energy is not a variable!
When you have unexpected enzyme data, you must also consider the possibility that other effects are happening. Unless you are working with an extremely well-characterized enzyme (including its interaction with the substrate and the inhibitor), you may not have a 'textbook' process.
You must not forget the thermodynamics of the ENTIRE enzyme process! By adjusting temperature, you are almost surely changing enzyme-ligand binding equilibrium as well as likely altering enzyme activity itself. For binding, the curve may not be linear with respect to temperature, it may even have an inflection, and, most importantly, the effects may be different for binding of the substrate and binding of the inhibitor (regardless of the mode of the inhibitor's function). In this light, temperature can be a very confusing variable. Also don't forget to verify that temperature is not somehow effecting your reporter system!! If you're using fluorescence, it can be surprisingly altered by temperature (but it's easy to check this).
I would suggest a far more careful 2-parameter study of concentrations of both substrate and product, at a fixed enzyme concentration and fixed temperature.
I think you're confused. Could you give us an example of your data ( Vap, Kap for the different inhibitor concentrations) and the model that you are using)?
By the way,it is possible that activation energy changes in a enzymatic reaction. This happen when three dimensional structure of the enzyme has changed due to a significant change in environmental conditions. (See Dixon´s textbook for details). However it does not seem your situation.
Regards
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