Hemoglobin is the oxygen transport protein found in blood. Hemoglobin is made up of four polypeptides. It provides a model of the properties that a quaternary structure confers on a protein, in particular allostery . Myoglobin is the oxygen storage protein found in muscle. Both myoglobin and hemoglobin contain a prosthetic group .
Prosthetic groups are non-polypeptide groups.
There are many different types. They are often found tightly bound to proteins and are usually required for activity. A protein that is missing its prosthetic group is called an apoprotein . Many enzymes also contain prosthetic groups. The prosthetic group in myoglobin and hemoglobin is called the heme .