Which hemoglobin contains four gamma chains and has an extremely high affinity for oxygen?

Which hemoglobin contains four gamma chains and has an extremely high affinity for oxygen?

• A. Hb Barts
• B. Hb Gower I
• C. Hb Portland I
• D. Hb F

Answer: (A)

Hemoglobin oxygen binding is shaped by which globin chains come together. Hb Bart’s is an abnormal tetramer made of four gamma chains (γ4). It appears when alpha-globin production is severely reduced or absent, so the gamma chains that would normally pair with alpha instead form this four-gamma tetramer. This γ4 configuration binds oxygen extremely tightly and does not release it well to developing tissues, effectively causing little oxygen delivery to the fetus and contributing to a severe condition called hydrops fetalis. In contrast, Hb F is the usual fetal form with two alpha and two gamma chains (α2γ2), which, while it has relatively high oxygen affinity, does not consist of four gamma chains. The other options are embryonic tetramers that include zeta chains (and/or different pairings) and do not match the four-gamma composition described here.

Hemoglobin oxygen binding is shaped by which globin chains come together. Hb Bart’s is an abnormal tetramer made of four gamma chains (γ4). It appears when alpha-globin production is severely reduced or absent, so the gamma chains that would normally pair with alpha instead form this four-gamma tetramer. This γ4 configuration binds oxygen extremely tightly and does not release it well to developing tissues, effectively causing little oxygen delivery to the fetus and contributing to a severe condition called hydrops fetalis.

In contrast, Hb F is the usual fetal form with two alpha and two gamma chains (α2γ2), which, while it has relatively high oxygen affinity, does not consist of four gamma chains. The other options are embryonic tetramers that include zeta chains (and/or different pairings) and do not match the four-gamma composition described here.