Definition: Enzyme (en-zay-mo) is a protein that catalyzes a chemical reaction in living organisms.
Definition: A catalytic enzyme is an enzyme whose activity is regulated by its catalytic site, which is a region where it binds to substrate molecules and activates the catalytic site. It is also known as a biocatalyst, which refers to the ability of a biological system (usually the host cell) to catalyze chemical reactions under normal conditions without the need for an enzyme active in that particular reaction.
In other words, enzymes are proteins with the ability to catalyze chemical reactions in living organisms.
Enzymol