The area where substrates and co-factors bind to the enzyme is called the active site. This is where the catalysis takes place. An active site often appears like a pocket, and consists of several amino acids which can have specific interactions with the substrate . Figure 1 shows the active site of alcohol dehydrogenase where NAD+ binds. Amino acid residue 47, which is responsible for the Alcohol Flush syndrome is located in this active site, and this amino acid is important in binding to NAD+. If a mutation causes an amino acid substitution on this residue, the kinetic parameters may therefore be altered, which is the case in the Alcohol Flush syndrome.
Figure 1: Surface model of alcohol dehydrogenase showing the active site (blue) for NAD+ (red) binding. Generated with PyMOL from PDB entry 1HSZ