In particular we are going to discuss the functions of globular proteins, emphasizing how their structure and function are related. The largest group of globular proteins are the enzymes , which catalyze nearly all of the chemical reactions that take place in biological systems. First, though, we will look at oxygen transport and storage proteins, myoglobin and hemoglobin . They were the first proteins to have their 3-dimensional structures determined.
Oxygen plays a primary role in the energy yielding reactions of biological systems.
Higher level organisms have developed circulatory systems for delivering oxygen to the various tissues. Because oxygen has a fairly low solubility in water, these organisms have evolved transport and storage proteins to deliver large quantities of oxygen to the tissues. 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 .