Reading: Enzymes
Enzymes are proteins that have the ability to bind substrate in their active site and then chemically modify the bound substrate, converting it to a different molecule — the product of the reaction. Substrates bind to enzymes just like ligands bind to proteins. However, when substrates bind to enzymes, they undergo an enzyme-induced chemical change, and are converted to products.
The substrate binds to the enzyme by interacting with amino acids in the binding site. The binding site on enzymes is often referred to as the active site because it contains amino acids that both bind the substrate and aid in its conversion to product.
You can often recognize that a protein is an enzyme by its name. Many enzyme names end with –ase. For example, the enzyme lactase is used to break down the sugar lactose, found in mammalian milk. Other enzymes are known by a common name, such as pepsin, which is an enzyme that aids in the digestion of proteins in your stomach by breaking the peptide bonds in the proteins.
Enzymes are catalysts, meaning that they make a reaction go faster, but the enzymes themselves are not altered by the overall reaction. Examine this image to see how enzymes work.
The amino acids in the active site of enzymes play two roles, and sometimes those roles overlap. Some of the amino acids in the active site are responsible for binding of the substrate and others are responsible for facilitating the chemical reaction. Enzymes are generally quite specific for their substrates. Although lactase and pepsin both catalyze the same type of reaction, breaking a bond using water (hydrolysis: “hydro” means “water” and “lysis” means “to break”), lactase only functions when lactose is its substrate and pepsin can only break peptide bonds.