What are enzymes ?
They are biocatalysts that act on a substrate and then convert it into product. They usually have the suffix -ase.
Most of enzymes are proteins. Enzymes follow the physical and chemical reactions of proteins. They are heat labile and water soluble.
Enzymes are classified into:
Function : Transfer of hydrogen or addition of oxygen (oxidases, oxygenases and dehydrogenases).
AH2 + B ————-→ A + BH2
- Lactate dehydrogenase (NAD).
- Glucose-6-phosphate dehydrogenase (NADP).
- Succinate dehydrogenase (FAD).
Function: Transfer of groups other than hydrogen.
Example: Aminotransferase. (Subclass: Kinase, transfer of phosphoryl group from ATP; e.g. Hexokinase)
Function : Cleave bond and add water.
Acetyl Choline + H2O —-Acetylcholine-esterase—-→ Choline + Acetate
Function : Cleave without adding water.
- HMG CoA lyase.
- ATP Citrate lyase.
Function: Intramolecular transfers.
They include racemases and epimerases.
Example: Triose phosphate isomerase.
Function : ATP dependent condensation of two molecules.
- Acetyl CoA carboxylase.
- Glutamine synthetase.
- PRPP synthetase.
Note: The difference between Synthetase and Synthase :
- Synthetase : ATP-dependent enzymes catalysing biosynthetic reactions so according to the previous classification they belong to Ligases. (notice the T mnemonics)
- Synthase: enzymes catalysing biosynthetic reactions, but they do not require ATP directly.