Functional and computer modelling studies of haemoglobin from horse - The haemoglobin system of the Sardinian wild dwarf horse

A study was made of the haemoglobin (Hb) system from the Sardinian dwarf ho rse (Equus caballus jara), one of the last surviving wild horse species in Europe. The oxygen binding properties of the whole haemolysate and of the f our different horse Hbs, separated by ion-exchange chromatography, were stu died with special regard to the effect of chloride, 2,3-diphosphoglycerate and lactate. Results indicate that no significant functional differences ex ist between the four Hb components of horse haemolysate. Moreover, the mole cular basis of the intrinsically low oxygen affinity and of the weak intera ction of horse Hb with 2,3-diphosphoglycerate is discussed in the light of the primary structure of the molecule and of the results of a computer mode lling approach. On these bases, it is suggested that the Al (Thr-->Ser) and A2 (Pro-->Gly) substitutions observed in the beta chains from horse Hb may be responsible for the displacement of the A helix that is known to be a k ey structural feature of those Hbs that display an altered interaction with 2,3 -diphosphoglycerate as compared with human Hb.