What is the difference between deoxyhemoglobin and reduced hemoglobin?

Deoxyhemoglobin (Hb) and reduced hemoglobin (HbH) are two forms of hemoglobin, the oxygen-carrying protein in red blood cells. The difference between deoxyhemoglobin and reduced hemoglobin lies in their oxygenation status.

Deoxyhemoglobin is the form of hemoglobin when oxygen is not bound to the heme group, the iron-containing prosthetic group in hemoglobin. In deoxyhemoglobin, the iron in the heme group is in the ferrous state (Fe2+). Deoxyhemoglobin is the predominant form of hemoglobin in red blood cells when they are carrying oxygen from the lungs to the tissues.

Reduced hemoglobin, on the other hand, is the form of hemoglobin when oxygen is bound to the heme group. In reduced hemoglobin, the oxygen molecule is bound to the iron in the heme group, causing a change in the iron's oxidation state to the ferric state (Fe3+). Reduced hemoglobin is the form of hemoglobin in red blood cells when they are carrying oxygen from the tissues back to the lungs.

The transformation between deoxyhemoglobin and reduced hemoglobin is reversible and is facilitated by the binding and release of oxygen molecules. This process is central to the function of hemoglobin in oxygen transport within the body.