Classification of Enzymes :
Enzymes are classified into the following six main categories in according with the nature of reaction the catalyze:
1. Oxidoreductases : These serve to transfer hydrogen atoms or ions protons H+ or electrons e- from substrate molecules donors to other acceptors molecules:
Reduced S+ oxidized s1 → oxidized S + reduced s1
These enzymes are further classified into three categories
Alcohol dehydrogenases These transfer H+
Alcohol + NAD→ aldehyde+ NADH + H+
(Oxidized )( reduced)
Cytochrome oxidases: these transfer electrons;
Reduced cytochrome + o2 + 4H +→ oxidized cytochrome + 2H2O
Cntalases : These remove oxygen from 2H2O
2. Transferases: These transfer not H+ but some functional group or radical from a substrate molecule to another molecule.
S group + S1 → S+ S1- group
For example phosphorylase catalyzes phosphorylation of glucose or transferring a high energy phosphate bond from ATP to glucose.
3.Hydrolases : These catalyze hydrolysis of their substrates i.e. these split C-O-, C-H, C-C-. C-N and other similar bonds by addition of water.
SS+H2O→ H+S -OH
All digestive enzyme and the enzymes of lysosomes are hydrolases . Lysosomes enzyme serve for intracellular digestion of materials obtained by the cells from outside medium by endocytosis.
1. Lyases : These also bring about splitting of C-C,C-O, C-N,C-H, and other similar bonds not by hydrolysis but by elimination thereby leaving a double bond .conversely, these may add group to double bonds.
2. Insomerases : These catalyze structural changes in the moleclules of their substrates , resulting into formation of isomers.
3. Ligases: These catalyze linking of molecules of different compounds supplying energy of ATP to the reaction .For example ends of separate strands nucleic acid are joined by ligases.