ADAPTATION OF THE OXYGEN-TRANSPORT SYSTEM TO HYPOXIA IN THE BLUE-CRAB, CALLINECTES-SAPIDUS

Among the oxygen carrying proteins, two group are known to adapt to en vironmental challenges in the adult stage. Both vertebrate hemoglobins and arthropod hemocyanins adapt to chronic hypoxia by responding to t he actions of allosteric co-factors. The design strategy, however, dif fers fundamentally in the two groups. Even within the arthropods, chel icerate and crustacean hemocyanins respond to co-factors very differen tly. Only in the crustaceans does the oxygen carrier adapt by shifts i n intrinsic molecular properties. In hypoxic blue crabs, increases in the ratio of the primitive 1 x 6-meric oligomer bring about a higher o xygen affinity relative to that in normoxic animals, in which greater proportions of tile derived 2 x 6-meric oligomer are responsible for a lower oxygen affinity.