6.6 Summary of Section 6
The majority of proteins of known function are enzymes. Enzymes are biological catalysts, increasing the rates of reactions. Enzymes are not permanently altered by catalysis of a reaction.
The transition state is an unstable intermediate enzyme–substrate complex in which the enzyme and the substrate are in highly strained conformations.
There are a number of different catalytic mechanisms employed by enzymes including general acid and general base catalysis, covalent catalysis and electrophilic catalysis.
General acid and general base catalysis involve charged groups at the active site of the enzyme that help make and break bonds by causing a redistribution of electrons in the bonds of the substrate.
Lysozyme hydrolyses glycosidic bonds in the polysaccharides of bacterial cell walls. It uses both general acid and general base catalysis.
Carboxypeptidase A hydrolyses C-terminal peptide bonds and uses both electrophilic and general base catalysis. In binding its substrate, carboxypeptidase A undergoes a dramatic structural rearrangement to create the required active site conformation for catalysis. This process is known as induced fit.
The efficiency of enzyme-catalysed reactions in the cell is increased by metabolic channelling in multienzyme complexes, in which the product of one reaction is passed to the next enzyme in a pathway. Since the metabolite does not diffuse into the general aqueous environment, it is effectively concentrated near the enzyme.