Introduction to Enzymes
Part VI
Part VI. How do enzymes catalyze a reaction???
One answer is: Like all catalysts, enzymes decrease the energy required to get a reaction started. This was illustrated in the first part of this lecture with an energy diagram. Below is shown a similar diagram with more detail for the energy pattern for the enzyme catalyzed reaction. First, energy is required to form the complex between the enzyme and substrate (E-S complex) which is a higher energy state than the free enzyme and substrate/product.
Figure 11. Diagram of energetics of enzyme catalyzed reaction versus non-catalyzed reaction.
Another answer is more difficult to describe:
Enzymes use binding energy from the binding of substrates to assist in catalysis. Because the enzyme is flexible, the framework can "absorb" energy in a very efficient way and put this energy to use for assisting with catalysis.
Enzyme + Substrate = ComplexThis binding releases energy (See Figure 11 for illustration of the energy release on binding of substrate to the enzyme). However, calculations of the energy released show it is smaller than expected. The conclusion is that enzyme took up some of the binding energy. This absorbed energy taken up by the framework of the enzyme is used by it to assist in catalysis. Thus, this helps explain why enzymes are so large - that is the enzyme has a large framework in order to use it as a resource to store binding energy made available when the substrate binds to the enzyme which it can later use to drive the formation of products. For all this energy exchange to be efficient, the enzyme must be very flexible.E + S = ES Complex
Summary of Enzyme Catalysis:
1. Enzymes bind substrate with great specificity
2. Enzymes usually have no side products
3. Enzymes use energy released when substrates bind to make their catalysis more effective.
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu