A fetal-maternal shift in the oxygen equilibrium of hemoglobin from the viviparous caecilian, Typhlonectes compressicauda

1. 1. The equilibria and kinetics of oxygen binding by blood and hemoglobin from adult and fetal caecilians, Typhlonectes compressicauda, have been measured. 2. 2. The oxygen affinity of fetal blood is higher than that of adult blood. 3. 3. Electrophoresis of adult and fetal hemoglobins suggests that they may be identical: a major and minor component occurs in each. 4. 4. Adult and fetal hemoglobins have identical oxygen equilibria. Stripped hemoglobins have a high oxygen affinity and no Bohr effect between pH 6.5 and 10.0. An "acid", reversed Bohr effect is present below pH 6.5. The addition of 1 mM ATP reduces the oxygen affinity markedly and produces a moderate, normal Bohr effect. 5. 5. The major nucleoside triphosphate in fetal and adult erythrocytes is adenosine triphosphate: about 10% of the nucleoside triphosphates is guanosine triphosphate. Adult erythrocytes contain 3 times as much ATP as do the fetal erythrocytes. 6. 6. The fetal to maternal shift in the oxygen equilibrium is mediated entirely by the difference in ATP content of the maternal and fetal red blood cells.