TRANSITION FROM WATER TO AIR BREATHING - EFFECTS OF CO2 ON HEMOGLOBIN FUNCTION

The pH dependence of the specific effect of CO2 (pCo2 = 30 torr) on oxygen equilibria has been measured for the hemoglobins of four species of fish and one amphibian. Leiostomus xanthurus (marine teleost). Brachyplatystoma sp. (Amazonian catfish), Hoplosternum littorale (air-breathing catfish), Lepidosiren paradoxa (air-breathing lungfish), and Typhlonectes compressicauda (a caecilian). The blood CO2 content of air-breathing fish and amphibians 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 effect, the effect of CO2 on the oxygen affinity was very similar for all but that of the catfish, Brachyplatystoma 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, and was about half that produced by CO2 for human Hb A. This suggests that half the chains of each hemoglobin may have blocked amino terminal groups, except possibly Brachyplatystona s.p. hemoglobin. © 1979, Pergamon Press Ltd. All rights reserved.