Enzyme
A biological catalyst, almost always a protein, that accelerates a specific biochemical reaction.
Unit
Dimensionless
In depth
Enzymes lower activation energy by binding the substrate in an active site that stabilises the transition state, achieving rate enhancements of up to 10¹⁷. They work under mild conditions, are regulated by inhibitors and activators, and are highly sensitive to pH and temperature.
Examples in the real world
Amylase in saliva, pepsin in the stomach, and DNA polymerase copying the genome with astonishing fidelity.