Answer:
D. increasing protonation of β-chains His 146 with decreasing pH (i.e., higher H concentration) which stabilizes the T state conformation of Hemoglobin.
Explanation:
Human Hemoglobin is a tetrameric protein: consists of two α- and two β-subunits, and is organized as a dimer of two identical αβ dimers to form an (αβ)2 tetramer. Each subunit contains one heme group to which one O2 molecule binds reversibly. Hemoglobin principally has T low oxygen affinity state and R high oxygen affinity state, deoxyHb and fully liganded Hb respectively.
The binding of ligands such as H+, Cl- or BPG lowers the O2 affinity, in such way that affinity of hemoglobin towards oxygen O2 is decreased, when acidity of the environmental solution increases. So, when pH decrease acidity increases, there are more H+ available who bind to His 146 in β1 and β2 respectively. After that, O2 is released.
