Temperature dependence of haemoglobin-oxygen affinity in heterothermic vertebrates: mechanisms and biological significance.

摘要: As demonstrated by August Krogh et al. a century ago, the oxygen-binding reaction of vertebrate haemoglobin is cooperative (described sigmoid O2 equilibrium curves) and modulated CO2 protons (lowered pH) that – in conjunction with later discovered allosteric effectors (chloride, lactate organic phosphate anions) enhance unloading from blood relatively acidic oxygen-poor tissues. Based on exothermic nature oxygenation haem groups, haemoglobin–O2 affinity also decreases rising temperature. This thermal sensitivity favours oxygen warm working muscles, but may become detrimental regionally heterothermic animals, for example cold-tolerant birds mammals warmbodied fish, where it perturb balance between requirement organs substantially different temperatures than at respiratory thus commonly reduced or obliterated. Given linked endothermic release effectors, increased effector interaction an effective strategy widely exploited to achieve adaptive reductions temperature dependence blood-O2 affinity. The molecular mechanisms implicated vertebrates taxonomic groups reveal remarkable variability, both as regards (protons tunas, phosphates sharks billfish, chloride ions ruminants anions extinct woolly mammoth, etc.) binding sites same indicating multiple evolutionary origins, convergent physiological functionality (reductions O2-binding safeguard tissue supply).