Transição da respiração aquática para a aérea: efeitos do CO₂ sobre a função de hemoglobina ^*

Summary

The pH dependence of specific effect of CO₂ (pCO₂ = 30 torr) on oxygen equilibria has been measured for the hemoglobins of four species of fish and one anphibian: Leiostomus xanthurus (marine teleost), Brachyplatystoma sp. (Amazonian catfish), Hoplosternum Littorale (air-breathing catfish), Lepidosiren paradoxa (air-breathing lung-fish), and Typhlonectes compressicauda (a Caecilian). The blood CO₂, content of air-breathing fish and anphibians is considerably higher than that of water breathers, yet the hemoglobins examined from the air breathers showed no special adaptation to the increased CO₂ load. Although the effect of pH on the oxygen equilibria of the different hemoglobins varied greatly from Root effect to reverse Bohr effet, the effect of CO₂on the oxygen affinity was very similar for all but that of the catfish, Brapehyplatystoma sp., for which the effect was somewhat larger. The drop in oxygen affinity brought about by CO₂ increased with increasing pH for each hemoglobin examined. The change in the Bohr effect, Δ log P₅₀/Δ pH measured at pH 7.5 was similar for all five hemoglobins, about half that produced by CO₂ for human Hb A, This suggests that half the chains of each hemoglobin may have blocked grupos terminais aminos.