Oxygen‐binding properties of hemoglobins from estivating and active African lungfish

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Abstract
The oxygen‐binding characteristics and the multiplicity of the stripped hemoglobin from active lungfish Protopterus amphibius, are the same as in specimens that have been estivating for about 30 months, showing that alteration in the hemoglobin molecules is not involved in the earlier reported increase in oxygen affinity of whole blood during estivation (Johansen et al., '76). At pH 7.0 and 26°C the hemolysates show a high oxygen affinity (P50 = 3.1 Torr), a Bohr factor (Δ log P50/Δ pH) of −0.33, and a cooperativity coefficient (n) of 1.7. Between 15 and 26°C, the apparent heat of oxygenation (ΔH) is −8.6 Kcal·mole−1 at pH 7.0, corre‐sponding with data for other fish. A low sensitivity of oxygen affinity to urea appears to be adaptive to the high urea concentrations in estivating lungfish. The salt sensitivity is, however, similar to human hemoglobin. The hemoglobin consists of two major (electrophoretically anodal) components, which differ slightly in oxygen affinity but are both sensitive to pH and nucleoside triphosphates (NTP). Guanosine triphosphate (GTP), the major erythrocytic organic phosphate, however, depresses the oxygen affinity of the composite and separated hemoglobins more effectively than ATP suggesting that GTP is the primary modulator of oxygen affinity. Comparative measurements reveal only one major hemoglobin component in P. annectens which has a markedly lower oxygen affinity and phosphate sensitivity than P. amphibius hemoglobins and thus seems less pliable to phosphate‐mediated variation in oxygen affinity. The data are discussed in relation to the hemoglobin systems of other fish.