CO2 binds to hemoglobin's ___________ to stabilize the T state.

To understand why the N-terminus is the correct answer, it's important to consider the function of hemoglobin and how it interacts with carbon dioxide (CO2). Hemoglobin exists in two states: the R (relaxed) state and the T (tense) state. The T state is associated with lower affinity for oxygen and is stabilized when hemoglobin binds to CO2.

CO2 primarily binds to the N-terminus of the alpha and beta chains of hemoglobin, forming carbamino compounds. This binding effectively helps promote the release of oxygen in tissues where CO2 concentration is high, such as actively metabolizing cells. When CO2 binds to the N-terminus, it facilitates the conversion of hemoglobin to the T state, which reduces its oxygen affinity. This action is crucial for ensuring that oxygen is released where it is most needed.

The other choices do not accurately describe where CO2 binds to stabilize the T state. The C-terminus is involved in other forms of hemoglobin regulation and binding interactions but is not the primary site for CO2 binding that stabilizes the T state. The term "midpoint" is not relevant to the biochemical context of hemoglobin's function, and while side chains of the amino