Hemoglobin is a protein found in red blood cells, serving as the primary component responsible for the transport of oxygen from the respiratory system to peripheral tissues throughout the body. Structurally, it is a metalloprotein, meaning it incorporates metal ions, specifically iron, which are contained within prosthetic groups called heme. These heme units contain the binding sites for oxygen. The molecule is characterized by its cooperative binding properties, meaning the binding of one oxygen molecule to one subunit increases the affinity of the remaining subunits for additional oxygen. This mechanism allows for efficient saturation in the high partial pressure environment of the lungs and a rapid, steep release of oxygen in the low partial pressure environment of metabolically active tissues.