Key observations that led to the induced fit model being proposed include;
- More than one substrate can bind to an enzyme, however only the true substrate causes the proper alignment to cause a reaction
- Large molecules like proteins are not rigid, they are flexible. This is in contrast to the rigid model proposed in the lock and key model.
- Modern analytical techniques have mapped the changes in the active site during a chemical reaction.
The induced fit model proposes that the active site continues to change until the substrate completely binds to it. The proper alignment of the substrate with the active site causes the chemical reaction to take place at a faster rate. (The activation energy is lowered.)
As outlined in the flow chart, the induced fit model needs to be supported by experimental evidence. All analysis of experimental results to date supports this hypothesis.
Indeed in this experiment, the fact that the reaction rate became constant after 20 seconds supports the model. At this point all the active sites were occupied and thus could only produce a certain amount of product. The addition of sulphuric acid to terminate the reaction also supports the induced fit model. The acid denatures the active site.
Numerous experiments and techniques have been completed to test the hypothesis that active site changes during the binding of the substrate. In addition these structural changes have been mapped using x ray crystallography and the mapping of electron distributions. Therefore the model is now accepted as a useful model to determine the action of enzymes.
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