The Oxygen Affinities of Certain Invertebrate Haemoglobins

Abstract

1. A method is described for measuring the oxygen affinity of haemoglobin in small sample of whole or slightly diluted blood or coelomic fluid. 2. The oxygen affinity of the haemoglobins of the following invertebrate animals is high: Chironomus riparius, Tubifex sp., Ceriodaphnia laticaudata, Thalassema neptuni, Arenicola marina, Planorbis corneus, Daphnia magna. The oxygen pressure in millimetres of mercury for 50% oxyhaemoglobin at 17° C. in the absence of carbon dioxide varies, in the order of species just given, from 0.6 for Chironomus to 3.1 for Daphnia. This may be compared with 27 for human whole blood at 20° C. and pH 7.4. 3. A carbon dioxide concentration of 1% of an atmosphere has no measurable effect on the oxygen affinity of Chironomus haemoglobin. In the other invertebrates studied this concentration of carbon dioxide increases the oxygen affinity by about 1½ times, which is less than half its effect on human haemoglobin. 4. When the haemoglobins of Tubifex, Chirononmus, Daphnia and Planorbis are becoming deoxygenated in the animal there is a much lower oxygen pressure in the blood than in the water outside the animal. This means a steep gradient of oxygen pressure across the body wall. Consequently, for the animal to pick up oxygen from water containing little, but still considerable, quantities of the gas, haemoglobin of high oxygen affinity is essential.