Cellular regulation of an allosteric modifier of fish haemoglobin

Abstract

ADENOSINE TRIPHOSPHATE (ATP) is the major organic phosphate in the red blood cells of a wide variety of fish species^1–4. Its role as an allosteric modifier of fish haemoglobins is similar to that of 2,3-diphosphoglycerate (2,3-DPG) in mammalian red blood cells, in that it decreases the affinity of haemoglobin for oxygen^5,6. After exposure to the anoxia of high altitude or in certain conditions of anaemia, mammals increase red blood cell 2,3-DPG to facilitate oxygen unloading at the tissues⁷. By contrast, eels have been shown to decrease erythrocyte organic phosphate (that is, ATP) and increase haemoglobin–oxygen (Hb–O₂) affinity when acclimated to low environmental oxygen⁸. To test if this phenomenon was expressed in another fish species, we acclimated Fundulus heteroclitus, a euryhaline minnow, to hypoxic conditions. Our finding that this fish also lowered red blood cell ATP by as much as 40% (Fig. 1) suggests that this is a general response to hypoxia among water-breathing vertebrates.