The influence of environmental salinity on hemocyanin function in the blue crab, Callinectes sapidus.

The effects of inorganic ions and of the hydrogen ion on oxygen-binding properties of most respiratory pigments are opposite. The addition of salt to the medium increases oxygen affinities, and the addition of H+ decreases oxygen affinities of crustacean hemocyanins. These oxygenation properties, as observed in vitro, suggest that the oxygen-transport system must adapt to ionic changes in the blood. In fact, decreases in the salt concentration of the blood of estaurine blue crabs are accompanied by increases in pH, probably resulting from the input of ammonia produced in deamination of the intracellular pool of free amino acids as the cells conform to osmotic changes in body fluids. The result is a stability of hemocyanin function until the blood becomes very dilute. As the acclimation salinity is reduced from 35 to 15 o/ooo, the ionic effects on respiratory transport are balanced and there is no change in total oxygen uptake. At 5 o/ooo salinity, however, the higher blood pH is manifested in an elevation of the total oxygen concentration of prebranchial blood, probably because the Bohr shift is no longer opposed by a critical level of salt in the blood. Under these conditions the role of hemocyanin in aerobic respiration is reduced at high environmental oxygen levels, but it may be enhanced in hypoxic uaters.     

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.