Enzyme classification

Several  enzymes  are  named  through  adding  the  suffix  ‘-ase’  to  the  name  of  their substrate.  Therefore urease is the enzyme which catalyzes the hydrolysis of urea and 6-bisphosphatase hydrolyzes fructose-1, fructose-1, and 6-bisphosphate. Moreover, other  enzymes,  like  as  chymotrypsin  and trypsin ,   have  names  which  do  not indicate   their  substrate.   Some   enzymes   have various   another   names.

Figure:  Schematic representation of the substrate-binding sites in the serine proteases (a)trypsin, (b) chymotrypsin and (c) elastase.

To rationalize enzyme names, a system of enzyme nomenclature has been internationally approved.  This system wills places all enzymes into one of six major classes based on the kind of reaction catalyzed. Each enzyme is then distinctively identified with a four-digit classification number. Therefore trypsin has the Enzyme Commission  (EC) number 3.4.21.4, where the first number (3) indicates in which it is a hydrolase,  the second  number  (4) which it is a protease  which hydrolyzes  peptide bonds,  the third  number  (21) that  it is a serine  protease  with  a critical  serine residue  at the active  site and  the fourth  number  (4) denote  that  it was  the fourth  enzyme  to be assigned  to this class. For contrast, chymotrypsin has the Enzyme Commission number 3.4.21.1 and elastase 3.4.21.36.