Anion modulation of the negative Bohr effect of haemoglobin from a primitive amphibian

Abstract

THE Congo eel (Amphiuma means) is a primitive salamander that respires through its lungs, gills and integument. It lives in swamps, ditches and rice fields in the south-eastern USA. When pools and swamps become stagnant and water levels drop, Amphiuma will burrow and hibernate in the mud. In this letter we report that when organic phosphate cofactors are low or absent, as might be true during hibernation, the haemoglobin of this amphibian has unusual properties which may help the animal to extract oxygen from a low pH environment. The molecular adaptation exhibited by Amphiuma haemoglobin is a pH dependence of oxygen binding that is reversed relative to that of most haemoglobins. Low pH brings about a large increase in the oxygen affinity of stripped Amphiuma haemoglobin. This negative Bohr effect indicates that protons are bound as oxygen is bound. This is in contrast to the release of protons that usually accompanies oxygenation. New Bohr groups must be present in this amphibian haemoglobin, or the normal Bohr groups must be drastically modified. From a physiological viewpoint it is of interest that the Bohr effect in vitro is subject to regulation by organic phosphate cofactors.