Which form of hemoglobin has the lowest affinity for oxygen?

The form of hemoglobin that has the lowest affinity for oxygen is the tense form, often referred to as the T state. In this state, the hemoglobin molecule is more compact and less able to bind oxygen effectively. The T state is predominant when the hemoglobin is in the environment of high carbon dioxide concentration or low pH, conditions that commonly occur in actively metabolizing tissues. This decreased affinity for oxygen facilitates the release of oxygen where it is needed most.

In contrast, the relaxed form, or R state, of hemoglobin has a higher affinity for oxygen, enabling it to pick up oxygen effectively in the lungs, where oxygen concentration is high. By having a lower affinity for oxygen in the tense state, hemoglobin can release oxygen to tissues that require it without significant resistance. This differential affinity between the two states is crucial for the proper function of hemoglobin in oxygen transport and delivery throughout the body.