Both adult and fetal hemoglobin have BPG bound to them. The fetuc obtains its O2 from...

Both adult and fetal hemoglobin have BPG bound to them. The fetuc obtains its O2 from the mother through the placenta. This would suggest...

A. fetal Hb binds BPG stronger than adult Hb

B. adult Hb binds BPG stronger than fetal Hb

C. the BPG binding affinities are the same

D. BPG binding has no direct effect

Explain

Solutions

Expert Solution

2,3-bisphosphoglycerate or 2,3-BPG is bound in both cases for fetal Hb and adult Hb in different extent. But it interacts less efficiently with fetal hemoglobin than adult hemoglobin. BPG binds with the deoxy form of Hb.BPG stabilizes the low oxygen affinity state (T state) of the oxygen carrier. It situates in the cavity of the deoxy- conformation and make salt bridges with lysine and histidine residues in the ß subunits of hemoglobin. The R state, with oxygen bound to a heme group, has a different conformation and does not allow this interaction. BPG is a highly anionic compound found in hemoglobin whereas, histidine is positively charged and interacts well with the 2,3-BPG. As a result , it (Hb) becomes less effective for oxygen binding and more effective for BPG binding.

For fetal Hb, the positive histidine residues of HbA β-subunits that are essential for forming the 2,3-BPG binding pocket are replaced by serine residues in HbF γ-subunits. Serine has a neutrally charged side chain at physiological pH, and interacts less well. As a result, fetal Hb binds oxygen more effectively than that of adult Hb. So interaction of 2,3-BPG is less for fetal Hb compared to adult Hb, hence adult Hb binds BPG stronger than fetal Hb.

Ans is B)

queen_honey_blossom answered 1 year ago

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