MBB 222 Study Guide - Midterm Guide: Hemoglobin, Fetus
20 Dec 2018
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Figure 6. 26 illustrates this principle by showing that the high concentration of o2 in the lungs favors the r state, whereas a lower o2 concentration in the tissues favors the t state. Because 2,3-bpg concentration is constant in red blood cells, the equilibrium shift between the. R and t states is facilitated by the difference in po2 between the tissues and lungs, rather than by a change in 2,3-bpg concentration. 2,3-bpg binding traps hemoglobin (hb) in the t state by interacting with numerous residues in the center of the hemoglobin tetramer. Figure 6. 24 shows where 2,3-bpg binds between the two subunits. The r state of hemoglobin has a smaller central cavity (see figure 6. 17), so 2,3-bpg binds preferentially to the t state. 2,3-bpg is a classic heterotropic negative allosteric regulator because binding of 2,3-bpg to a secondary site inhibits binding of o2 to the primary sites.
