Enzymes are just a type of proteins with a catalytic function and proteins are made by amino acids.
You have to think in a protein as a whole but as an amino acid chain too. There are different types of amino acids. Some of them have polarity an the others have not. Some of them are aliphatic amino acids some are aromatic. There are 3 with positive charge and 2 with negative charge.
All the properties of the amino acids have an important effect on how proteins fold themselves into a secondary tertiary or quaternary structure. So the protein fold depends on the amino acids which are part of that protein. Hydrophobic amino acids are in the inside of the protein while hydrophilic ones are on the surface.
If we change a single amino acid we can change the whole protein structure. This change produces a malfunction on the enzyme that can imply the death of the living form or at least a disease.