What characteristic of hemoglobin makes it an allosteric protein?

Hemoglobin is classified as an allosteric protein primarily because it undergoes conformational changes when it binds to oxygen. This characteristic is crucial for its function in oxygen transport and regulation. When one molecule of oxygen binds to hemoglobin, it induces a structural change that makes it easier for additional oxygen molecules to bind at other sites on the hemoglobin molecule. This cooperative binding is a hallmark of allosteric proteins, where the binding of a ligand at one site affects the properties of other binding sites.

The ability to exhibit conformational changes allows hemoglobin to effectively pick up oxygen in the lungs, where oxygen concentration is high, and release it in tissues where oxygen concentration is low. This adaptability is what defines its role as an allosteric protein, enabling efficient oxygen transport and delivery in the bloodstream.

Other characteristics mentioned, such as binding multiple substrates, are common in many proteins but do not specifically define allosteric behavior. The presence of iron in hemoglobin is a critical aspect of its ability to bind oxygen, but it does not directly pertain to its classification as allosteric. Hemoglobin is not classified as an enzyme with one active site; instead, it functions primarily to transport oxygen, contrasting with typical enzyme activity. Thus, the