Question

Compare the P₅₀ s of maternal hemoglobin, fetal hemoglobin and myoglobin.   Explain why the positions of the P₅₀ are adaptive.

Answer 1

*In P50 s of maternal hemoglobin, the P50 represents the partial pressure of a gas required to achieve 50% saturation of a particular binding sites. The normal P50 is 26.7mm Hg. P50 is the representation of hemoglobin-oxygen affinity. When hemoglobin oxygen affinity increases, the oxyhemoglobin dissociation curve shifts to the left and decrease P50. Maternal hemoglobin has a lower affinity for oxygen than fetal hemoglobin. That is, in P50 s of maternal hemoglobin, hemoglobin-oxygen affinity decreases, the oxyhemoglobin dissociation curve shifts to the right and increases P50.

*Fetal hemoglobin also known as hemoglobin F. It is oxygen carrier protein in human fetus. It is found in fetal red blood cells. Hemoglobin F has a different composition from the adult hemoglobin, which allows it to bind oxygen more strongly.In the newborn, levels of hemoglobin F gradually decrease. Hemoglobin F has high oxygen binding affinity. Hemoglobin F, has four subunits. Each subunit contain a heme group with an iron element which allows the binding of oxygen. As hemoglobin has 4 heme groups. Such aa, two alpha subunits and two gamma subunits.

* Myoglobin is a low molecular weight oxygen binding heme protein located primarily in heart and skeletal muscle cells. It consists of one heme group per molecule and has a structure similar to hemoglobin monomers.Iron within the heme group must be in tge Fe+2 state to bind oxygen. The total amount of myoglobin in an animal depends on body weight, degree of muscle development and myoglobin concentration in muscle. It receives oxygen from the red blood cells and transports it to the mitochondria of muscle cells, where the oxygen is used in cellular respiration to produce energy. Each myoglobin molecule has one heme prosthetic group located in the hydrophobic cleft in the protein.

High hemoglobin affinity for O2 that is, low PO2 at 50% saturation of hemoglobin could degrade exercise performance in normoxia by lowering mean tissue PO2 but could enhance O2 transport in hypoxic exercise by increasing arterial O2 saturation. The P50 shift is defined as the reported P50 minus the normal P50 and is used to quantify either a left shift or a right shift. Thus, the position of the P50 are adaptive.