Substrate binding at an active site

The amino acids present in the active site play an important role in enzyme function and this can be demonstrated by comparing the primary structures of the same enzyme from different organisms. In such a study, we would find that the primary structure would differ from species to species as a result of mutations lasting over millions of years. The variability would be proportional to how far apart the organisms are on the evolutionary ladder and this is one method of determining such a relationship. 

However, that does not concern us here. What does, is the fact that there are certain amino acids which remain constant, no matter the source of the enzyme. These are amino acids which are crucial to the enzyme s function and, as such, are often the amino acids which make up the active site. If one of these amino acids should be lost through mutation, the enzyme would become useless and an animal bearing this mutation would have a poor chance of survival. Thus, the mutation would not be preserved. (The only exception to this would be if the mutation either introduced an amino acid which could perform the same task as the original amino acid, or improved substrate binding.) 

This consistency of active site amino acids can often help scientists determine which amino acids are present in an active site if this is not known already. 

Amino acids present in the active site can have one of two roles. 

Binding—the amino acid residue is involved in binding the substrate to the active site. 

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