Adult and fetal haemoglobin J-Sardegna [alpha 50(CE8)His -> Asp]: functional and molecular modelling studies

Haemoglobin (Hb) J-Sardegna [alpha 50(CE8)His --> Asp] is a haemoglobin var iant characteristic of subjects from the island of Sardinia, Here we report a study of the functional properties of both fetal and adult Hb J-Sardegna . The results indicate that adult Hb J-Sardegna displays an oxygen affinity that is higher than that of adult Hb only in the presence of 2,3-diphospho glycerate (2,3-DPG), On the contrary, at 20 degrees C, the oxygen affinity of fetal Hb J-Sardegna is identical to that of normal fetal haemoglobin, bo th in the presence and in the absence of 2,3-DPG. A significant difference between these two systems (i.e. a higher oxygen affinity of fetal Hb J-Sard egna) shows up very clearly only when temperature is increased to 37 degree s C. Hence in fetal Hb, the main effect of the amino acid substitution is a decrease in the overall enthalpy change of oxygenation. The results outlin e the role of the alpha(1)-beta(1) interface in assessing the thermodynamic s of oxygen binding. The functional properties of both adult and fetal Hb J -Sardegna have been interpreted at the structural level in light of the res ults obtained by a computational modelling approach performed in comparison with HbA and Hb Aichi, a variant characterized by a different mutation [al pha 50(CE8)His --> Arg] at the same position.