oxyhemoglobine

Oxyhemoglobine, also called oxyhemoglobin, is the form of hemoglobin bound to molecular oxygen. It forms in the lungs when inhaled oxygen diffuses into red blood cells and binds to the ferrous iron (Fe2+) of each heme group in hemoglobin. A normal adult hemoglobin molecule (hemoglobin A, α2β2) contains four heme groups and can bind up to four O2 molecules. Oxyhemoglobin reversibly releases oxygen to tissues where PO2 is low, converting to deoxyhemoglobin. The iron in heme must be in the ferrous state; oxidation to ferric (Fe3+) yields methemoglobin, which cannot bind O2.

Binding characteristics: Hemoglobin exhibits cooperative binding; binding of one O2 increases affinity for additional O2, producing a sigmoid oxygen-hemoglobin dissociation curve. In the lungs, high PO2 favors loading; in tissues, lower PO2 favors unloading. Several factors modulate affinity: the Bohr effect (lower pH or higher CO2 reduces affinity, promoting oxygen release in active tissues), higher temperature shifts the curve to the right, and 2,3-bisphosphoglycerate (2,3-BPG) within red blood cells lowers affinity to optimize oxygen delivery at physiological pH.

Physiological role: Oxyhemoglobine is the primary oxygen carrier in arterial blood, delivering O2 to cells for metabolism. Measurement: saturation of hemoglobin with O2 is reported as SaO2 or SpO2 using blood gas analysis or pulse oximetry; in healthy individuals at sea level, values are typically around 95–100%.

Clinical relevance: Abnormalities such as methemoglobinemia, carboxyhemoglobinemia, or anemia impair oxygen transport and oxyhemoglobin levels, with symptoms ranging from mild hypoxia to organ dysfunction depending on severity.