Oxygen Transport in Diving Vertebrates

Abstract

Oxygen transport proteins have developed, during evolution, complex regulatory molecular mechanisms to optimize the oxygenation-deoxygenation cycle according to the physiological needs of a given species. Considering the variety of species that depend on hemoglobin for oxygen transport, these molecules must execute their primary function under extreme environmental conditions. In general, these mechanisms appear to be based on a thermodynamic linkage between binding of allosteric effectors (H+, CO₂ and C1⁻, as well as organic and inorganic phosphates) and the basic reaction of hemoglobin with O₂ [[1]]. For example, hemoglobins from Arctic mammals are characterized by a very low temperature sensitivity of oxygen binding, which has been interpreted as being beneficial to animals living in cold environments. Thus, with external temperature as low as −40°C, it is vital to reduce the overall AH of oxygen binding (generally exothermic, ΔH <0) as much as possible: deoxygenation will require much less heat and oxygen can still be released from the blood to the colder peripheral tissues. For this reason the hemoglobin of diving animals could be an interesting molecule for study since these mammals are specialized for prolonged dives, often in cold environments. We compared the hemoglobin systems from two species of whale: Balaenoptera physalus and Balaenoptera acutorostrata, which live in the Mediterranean and the Arctic seas, respectively. These species may have developed specific mechanisms for the maintenance of adequate oxygen supply to cold peripheral tissues in hypoxic conditions and in relation to their habitat.