In transporting O2 from the respiratory surfaces to the respiring tissues of animals, hemoglobin (Hb) directly links aerobic metabolism with O2 availability and is a paradigm for studying mechanisms of molecular adaptations. Hb-O2 binding is cooperative (described by sigmoid O2 binding curves) and decreased by allosteric effectors (protons, CO2, lactate, organic phosphates and chloride ions) that modulate O2 binding in response to changes in environmental and metabolic dictates. Hb-O2 affinity moreover decreases with rising temperature. This increases O2 unloading in warm tissues that consume more O2, but may be maladaptive – and thus is reduced - in regional heterothermic animals where it may hamper O2 unloading (in cold extremities of Artic mammals) or cause excessive O2 release (in warm organs of fast-swimming fish). Illustrated with case studies (estivating lungfish, high altitude frogs, birds and mammals - and recreated woolly mammoth Hb) the treatise reviews intraspecific and interspecific adaptations (that are mediated by changes in the levels of red cell effectors and in Hb structure, respectively) in response to changes in O2 availability and temperature, demonstrating reciprocity of compensatory adjustments at molecular, cellular and organismic levels of organization.
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Italian Physiological Society (SIF) & European Society of Comparative Physiology and Biochemistry (ESCPB) Conference, 2013