The unique chemical qualities of individual amino acids do not directly determine the function of an enzyme. What, then, is the role of the individual amino acid's unique chemical qualities, and what directly determines the function of an enzyme?
The unique properties of amino acids affect the formation of secondary and higher structures of protein. Each amino acid is characterized by the specific range of angles, which its backbone can form in the molecule. It affects the bending of polypeptide chain. The unique properties also affect interaction between proteins, and within protein molecule. Sickle cell anemia shows how change in one amino acid can result in abnormal protein conformation, caused by altered interactions between separate globin molecules.
Unique properties of amino acids could be useful during posttranslational modifications of proteins. For example, only serine and threonine can be phosphorylated. Also, the unique properties of amino acids are important in the active sites of enzymes. There, the unique properties allow their participation in catalysis. Only a small number of amino acids can be found in the active sites. Moreover, the specific reactions require the specific amino acids. For example, enzymes, which provide destruction of peptide bonds, must have serine in their active site.