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 horse (Equus caballus jara), one of the last surviving wild horse species in Europe. The oxygen binding properties of the whole haemolysate and of the four different horse Hbs, separated by ion-exchange chromatography, were studied with special regard to the effect of chloride, 2,3-diphosphoglycerate and lactate. Results indicate that no significant functional differences exist between the four Hb components of horse haemolysate. Moreover, the molecular basis of the intrinsically low oxygen affinity and of the weak interaction 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 modelling approach. On these bases, it is suggested that the A1 (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 key structural feature of those Hbs that display an altered interaction with 2,3-diphosphoglycerate as compared with human Hb.