Functional, spectroscopic and structural properties of haemoglobin from chamois (Rupicapra rupicapra) and steinbock (Capra hircus ibex)

Abstract

The functional and spectroscopic properties of chamois (Rupicapra rupicapra) and steinbock (Capra hircus ibex) haemoglobin (Hb) have been studied with special reference to the action of allosteric effectors and temperature. Moreover, the amino acid sequences of the N-terminal segments of the alpha- and beta-chains have been determined. The present results indicate that chamois and steinbock Hbs display a low affinity for O2, which appears to be modulated in vivo by Cl- ions rather than 2,3-bisphosphoglycerate. The Bohr effect for O2 binding to chamois and steinbock Hb is higher than for reindeer and bovine Hbs, being similar to that of human Hb. Moreover, the temperature-dependence of oxygenation appears intermediate between that of human and reindeer Hbs. E.p.r. and absorption spectroscopic properties of the ferrous nitrosylated derivative of chamois and steinbock Hbs suggest that both haemoproteins are in a low-affinity conformation even in the absence of InsP6. The reduced effect of polyphosphates on the functional and spectroscopic properties of chamois and steinbock Hb agree with amino acid differences in the N-terminal segment of the beta-chains (i.e. the deletion of Val(NA1) and the replacement of His(NA2), present in human Hb, and Gln(NA2), present in horse Hb, by Met). The molecular mechanism modulating the basic reaction of O2 with chamois and steinbock Hb may be linked to specific physiological needs related to the high-altitude habitats of these two animals.