Answer to Question #93375 in Biochemistry for Kylie

Question

Describe the four mechanisms by which enzymes catalyse reactions.

Answer 1

1. Acid–base catalysis. This type of enzyme catalysis is based on the participation of functional groups possessing the properties of a weak acid and a weak base. The spatial structure of the enzyme allows acidic or basic groups to be located in a limited volume in close proximity to the substrate. Amino acid residues that make up the active center have functional groups exhibiting the properties of both acids and bases.

2. Covalent catalysis. This type of catalysis is based on the attack of nucleophilic (negatively charged) or electrophilic (positively charged) groups of the active center of the enzyme with substrate molecules. This process leads to the formation of a covalent bond between the substrate and the coenzyme or functional group of the amino acid residue of the active center. The effects of serine proteases (i.e., trypsin, chymotrypsin, and thrombin) are examples of covalent catalysis.

3. Electrostatic catalysis. During the process of the electrostatic catalysis, the substrate displaces water from the active center. The mechanism resembles the process occurring in an organic solvent, where electrostatic interactions are stronger than in an aqueous solution. A change in the charge distribution at low dielectric constants can affect the reactivity of chemical groups. The transition state can be stabilized by the electric field of the ion.

4. Intramolecular catalysis. This type of catalysis is characterized by the presence of reactive groups in a substrate molecule. For example, the hydrolysis of the ether bond in aspirin is accelerated by intramolecular common basic catalysis.