Which protein in red blood cells carries oxygen around the body?

Hemoglobin is the protein in red blood cells that carries oxygen around the body.

Hemoglobin is an iron-containing protein packed inside erythrocytes. In the lungs, oxygen binds to iron atoms in hemoglobin's heme groups. Blood then transports that oxygen through arteries to tissues, where changing conditions encourage hemoglobin to release it for cellular respiration and energy production.

A typical mammalian hemoglobin molecule contains four globin protein subunits and four heme groups, allowing it to bind up to four oxygen molecules. Hemoglobin also contributes to the red color of blood. Its ability to bind oxygen cooperatively helps it load oxygen efficiently in the lungs and unload it in tissues.

Hemoglobin is not the same as myoglobin. Myoglobin is found mainly in muscle cells and stores or handles oxygen locally, while hemoglobin performs long-distance transport in blood. Hemoglobin also carries some carbon dioxide and helps buffer blood acidity. Low hemoglobin can contribute to anemia, whose symptoms may include fatigue, weakness, and shortness of breath.