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 species1–4. 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 oxygen5,6. 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.