Hb Bassett is a hemoglobin variant that exhibits a very reduced oxygen affinity (Abdulmalik et al., 2004).
Hb Bassett arises from a mutation at the alpha 94 (G1) position whereby aspartic acid is replaced by alanine (Abdulmalik et al., 2004). Hb Bassett is a disruption of the alpha1 and beta2 contact point (Voet and Voet, 2006, Abdulmalik et al., 2004). Hemoglobin of the Bassett variety has much higher P50 than normal hemoglobin. At pH 7, Hb Bassett has a P50 of approximately 22mmHg and normal hemoglobin has an approximate P50 of 10.5mmHg (Abdulmalik et al., 2004). In addition to high P50 values, Hb Bassett shows a reduced Bohr effect (reduced oxygen unloading) and low cooperativity (n=1.4) resulting in lower oxygen affinity (Abdulmalik et al., 2004). These factors conspire to produce a hemoglobin variant that does not provide sufficient oxygen and manifests itself as low oxygen saturation, episodes of cyanosis and anemia (Abdulmalik et al., 2004).
The proposed explanation for Hb Bassett’s instability is loosening and destabilization of the hemoglobin R state (bound ligand ) and a resulting shift in the equilibrium that exists between the two states towards the T state (unbound oxygen). The instability is localized at the interface between the two dimeric subunits of hemoglobin.
The lack of bound oxygen in Hb Bassett homozygotes leads to the clinical outcome of cyanosis (they are cyanotic) (Abdulmalik et al., 2004).