what are the two factors that contribute to the dissociation of oxyheamoglobin in the atrial blood to release molecular oxygen

Dear student,
The two major factors that contribute to the dissociation of oxyhemoglobin in the atrial blood to release the oxygen are -
i) CO2 

most of the CO2 is transported as bicarbonate ions and a small amount is dissolved in the blood plasma.
CO2 accumulation in the blood  causes carbamino compounds to be generated through chemical interactions, which bind to hemoglobin forming carbaminohemoglobin. it influences blood pH due to formation of bicarbonate ion
The formation of a bicarbonate ion releases protons (H+) into the plasma, increasing acidity and  shifts the oxygen dissociation curve to the right. all this results in increase in dissociation of oxygen from the hemoglobin molecule; as dissociation constant (Kd) of hemoglobin is inversely proportion to the oxygen binding affinty of hemoglobin).

ii)  
2,3- Bisphosphoglycerate (BPG)

It is an organophosphate formed in erythrocytes during glycolysis. The production of 2,3-BPG is an important adaptive mechanism. In deoxygenated state , hemoglobin binds one molecule of BPG in the central cavity formed by its four subunits.BPG forms salt bridges wit the terminal amino groups of both βchains of hemoglobin. it stabilizes deoxygenated hemoglobin by forming additional salt bridges andd there reduces the O2 affinity   of hemoglobin. it exerts its effect on O2 affinity of hemoglobin by binding to deoxyhemoglobin but not to hemoglobin. An increase in the concentration of BPG shifts the dissociation curve to the right, causing more O2 to be liberated.
 

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