Question

Fetal hemoglobin consists of two alpha subunits and two gamma subunits. The gamma subunits have different residues at the 2,3-BPG binding site compared to those found in the beta subunits. The charge characteristics of the different residues that are found in the gamma subunits allow for weaker binding to 2,3-BPG versus that seen in the case of adult hemoglobin, which contains two alpha subunits and two beta subunits. 

The statement is false. 

The statement is true.

Answer 1

The statement is true.
The greater affinity for oxygen can be explained by the lack of interactions by fetal hemoglobin with 2,3-bisphosphoglycerate (2,3-BPG). In adult red blood cells, this substance decreases the affinity of hemoglobin for oxygen. 2,3-BPG is also present in fetal red blood cells but interacts less efficiently with fetal hemoglobin than adult haemoglobin. This is due to a change in a single amino acid found in the 2,3-BPG 'binding pocket': from histidine to serine, which gives rise to the greater oxygen affinity.

Whereas histidine is positively charged and interacts well with the negative charges found on the surface of 2,3-BPG, Serine has a neutrally charged side chain at physiological pH and interacts less well. This change results in less binding of 2,3-BPG to fetal Hb, and as a result, oxygen will bind to it with higher affinity than adult hemoglobin.