Enzymes are macromolecular biological catalysts that accelerate chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products.

Naming and Classification

Except for some of the originally studied enzymes such as pepsin, rennin, and trypsin, most enzyme names end in “ase”. The International Union of Biochemistry (I.U.B.) initiated standards of enzyme nomenclature which recommend that enzyme names indicate both the substrate acted upon and the type of reaction catalyzed. Under this system, the enzyme uricase is called urate: O2 oxidoreductase, while the enzyme glutamic oxaloacetic transaminase (GOT) is called L-aspartate: 2-oxoglutarate aminotransferase.

Enzymes can be classified by the kind of chemical reaction catalyzed.

  • Addition or removal of water
    • Hydrolases - these include esterases, carbohydrases, nucleases, deaminases, amidases, and proteases
    • Hydrases such as fumarase, enolase, aconitase and carbonic anhydrase
  • Transfer of electrons Oxidases Dehydrogenases
  • Transfer of a radical
    • Transglycosidases - of monosaccharides
    • Transphosphorylases and phosphomutases - of a phosphate group
    • Transaminases - of amino group
    • Transmethylases - of a methyl group
    • Transacetylases - of an acetyl group
  • Splitting or forming a C-C bond
    • Desmolases
  • Changing geometry or structure of a molecule
    • Isomerases
  • Joining two molecules through hydrolysis of pyrophosphate bond in ATP or other tri-phosphate
    • Ligases


The text was excerpted from a Worthington publication which was originally published in 1972 as the Manual of Clinical Enzyme Measurements.