Nomenclature: typically end in -ase
Classifications
1) Oxidoreductases: catalyze redox reactions
2) Transferases: transfer groups of atoms between molecules
3) Hydrolases: catalyze hydrolysis reactions
4) Lyases: add to or make double bonds
5) Isomerases: isomerize molecules
6) Ligases or synthetases: join two molecules
Mechanism
E + S ---> E-S where E = enzyme S = substrate P = product
E-S ---> E-P where E-S = Enzyme-Substrate complex
E-P ---> E + P where E-P = Enzyme-Product complex
Models
Lock-and-key: exact fit of substrate into enzyme
Induced Fit: enzyme cavity shapes changes to accommodate substrate
Enzyme Structure
Active site: specific portion of enzyme which binds to substrate
Zymogen (proenzyme) enzyme + polypeptide fragment
Example: trypsinogen + enterokinase (pancreas) ----> trypsin + hexapeptide small intestine
Cofactor: nonprotein portions required by enzymes to complete their function
Coenzyme: organic cofactor
Apoenzyme: polypeptide portion which needs a cofactor to complete its function
Holoenzyme = apoenzyme + cofactor
Inhibition: process which makes enzymes less active or inactive
Competitive: inhibitor binds at active site preventing entry of substrate
Noncompetitive: binding at other than active site, changing the shape of the active site
Factors Affecting Enzyme Activity
1) Temperature
2 ) pH
3) Substrate Concentration
4) Enzyme Concentration
Enzyme Regulation