Augmented water binding and low cellular water content in erythrocytes of camel and camelids

We investigated a link between hemoglobin primary structure, hemoglobin hyd rophobicity-hydrophilicity, and erythrocyte water content in various mammal ian species. Some hemoglobin molecules, particularly those of the camel and camelids, contain more charged amino acid residues and are more hydrophili c than the hemoglobins of human and a number of other mammalian species. To test the in vivo significance of these alterations of hemoglobin primary s tructure, we determined the osmotically unresponsive erythrocyte water frac tions in mannit solutions of various osmolarities at 4 degrees C. Among the species investigated, the size of the osmotically unresponsive erythrocyte water fraction relates in a positive linear way to hemoglobin hydrophilici ty. The extreme low total erythrocyte water content of camel erythrocytes ( 1.1-1.3 g water/g dry mass) may be explained by a comparatively high osmoti cally unresponsive erythrocyte water fraction. It is proposed that alterati ons of hemoglobin sequences of camel and camelids may be the part of a natu ral selection process aimed at protecting these animals against osmotic deh ydration in arid environments.