Enzymes are classified into six main groups, depending on the type of reaction they catalyze:
Oxidoreductases: EC 1 ==> Oxidoreduction reaction
Transfers: EC 2 ==> Transfer of functional groups from one substrate to another
Hydrolases: EC 3 ==> Hydrolyses
Lyases: EC 4 ==> Breaking of different chemical bonds by means other than hydrolysis or oxidation
Isomerases: EC 5 ==> Isomerizations
Ligases or synthetases: EC 6 ==> Formations of covalent bonds coupled to the hydrolysis of a nucleoside triphosphate (generally ATP)
The main cut-out enzymes are EC 3 (hydrolases) and EC 4 (lyases).
Hydrolases are a class of enzymes that catalyze the hydrolysis reactions of molecules according to the general reaction:
R-R '+ H2O ⇌ R-OH + R'-H
In biochemistry, a lyase is an enzyme that catalyzes the breakdown of different chemical bonds by means other than hydrolysis or oxidation, thus often forming a new double bond or a new ring. For example, a lyase enzyme catalyzes the transformation reaction of adenosine triphosphate (ATP) into cyclic adenosine monophosphate (cAMP):
ATP → AMPc + PPi
Lyases differ from other enzymes in that they only require one reagent in the direct direction of the reaction, but two in the opposite direction:
Reaction: A ⇋ B + C