What is the term for H+ binding to HbO2 reducing its affinity for O2?

The term for H+ binding to hemoglobin (Hb) and reducing its affinity for oxygen (O2) is indeed best described by the concept of oxygen unloading. When H+ ions, which indicate an increase in acidity, bind to hemoglobin, they cause a conformational change in the protein that decreases its affinity for oxygen. This phenomenon is part of the Bohr effect, where an increase in carbon dioxide and H+ concentration leads to a reduction in hemoglobin's affinity for oxygen, facilitating oxygen release in tissues where it is needed most.

This process is crucial because it ensures that hemoglobin releases more oxygen in areas of high metabolic activity, such as exercising muscles, where CO2 and H+ concentrations are elevated. Thus, oxygen unloading is fundamentally linked to how effectively hemoglobin supplies oxygen to tissues based on their metabolic needs.