Enzymes are proteins which act as catalysts to facilitate the conversion of substrates into products.
Enzyme classification has been developed by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB), which arranges enzymes into six large families:
EC 1.-.-.- Oxidoreductases
EC 2.-.-.- Transferases (includes the protein kinases EC 2.7.-.-)
EC 3.-.-.- Hydrolases
EC 4.-.-.- Lyases
EC 5.-.-.- Isomerases
EC 6.-.-.- Ligases
Enzymes may also be grouped according to the physiological pathway or process in which they are involved. For example, L-arginine turnover, cyclic nucleotide turnover, eicosanoid turnover or chromatin modifying enzymes.
The majority of drugs which act on enzymes act as inhibitors and most of these are competitive, in that they compete for binding with the enzyme's substrate- for example the majority of the original (first generation) kinase inhibitors bind to the ATP pocket of the enzyme. Some inhibitors are non-competitive, binding away from the substrate binding domain, competing for co-factor/co-enzyme binding, or causing an allosteric conformational change in the 3-dimensional protein structure that prevents substrate interaction. Yet other inhibitors are irreversible and these covalently bind to the enzyme, permanently inactivating catalytic function (these are also known as suicide inhibitors).
The topics below highlight a cross-section of the clinical uses of enzyme inhibitors, from inflammation to cancer.