Hemoglobin is the iron-carrying protein found in red blood cells that binds to oxygen.

Hemoglobin is a crystallizable, conjugated protein consisting of an iron-containing pigment (called heme or hematin) and a simple protein, globin. In the lungs, it combines readily with oxygen to form a loose, unstable compound called oxyhemoglobin, a process called oxygenation.

In the tissues of the body, where oxygen tension is low and carbon dioxide tension is high, oxyhemoglobin liberates its oxygen in...