General acid catalysis involves donation of a proton by the catalyst. General base catalysis involves abstraction of a proton by the catalyst. The side chains of Asp, Glu, His, Cys, Tyr and Lys can be involved in general acid-base catalysis. Covalent catalysis involves rate enhancement by the transient formation of a catalyst-substrate covalent bond.
Covalent catalysis is a commonly employed mechanism in enzyme reactions.
The side chains of His, Cys, Asp, Lys and Ser can participate in covalent catalysis. The coenzymes pyridoxal phosphate and thiamine pyrophosphate function mainly by covalent catalysis. Metal ion catalysis is widely used. Binding substrates in the proper orientation. Mediating oxidation-reduction reactions.