“Inhibitors which bind irreversibly to an enzyme often form a covalent bond to an amino acid residue at or near the active site and permanently inactivate the enzyme”. Susceptible amino acid residues include which of the following?

Ser and Cys residues have reactive –OH and –SH groups respectively. The compound diisopropylphosphofluoridate (DIPF) reacts with Ser residue in the active site of the enzyme acetylcholinesterase, irreversibly inhibiting the enzyme and preventing the transmission of nerve impulses. Iodoacetamide modifies Cys residues and hence, may be used as a diagnostic tool in determining whether one or more Cys residues are required for enzyme activity.