Urea and chloride sensitivities of coelacanth hemoglobin

Synopsis

At pH 6.96–6.98, 20°C and in the absence of inorganic ions, the O₂ affinity of thawed Latimeria chalumnae hemoglobin was 1.53–1.86 mmHg; cooperativity was 1.00–1.13. These values are essentially the same as those in the literature for samples that had never been frozen. There was no clear effect of either urea (up to> 3M) or KCl (up to> 1M) on O₂ binding. Thus the hemoglobins of the coelacanth, as well as those of most of the elasmobranchs examined, are insensitive to urea, a major intracellular osmolyte in these groups and a denaturing agent in higher vertebrates. However, the absence of comparable information on more primitive hemoglobins and also on teleost hemoglobins precludes a clear evolutionary interpretation of the origin of urea sensitivity of the hemoglobins in higher vertebrates.