TEMPERATURE-DEPENDENCE OF OXYGEN-BINDING TO CEPHALOPOD HEMOCYANINS - ECOLOGICAL IMPLICATIONS

The present paper discusses the temperature sensitivity and the contro l of oxygen binding to haemocyanins of several species of cephalopods, using a similar ionic composition to their blood in vivo. Based on th e relationship between the oxygen affinity and the cooperativity of ox ygen binding of the cephalopods at their habitat temperatures, we may divide them into three groups: 1) the octopuses plus the sluggish gian t squid, Architeuthis, and Nautilus, with P-50 values in the range 10- 20 mm Hg; 2) the fast swimming squids with P-50 values around 30 mm Hg ; 3) and the Sepia species with P-50 values above 30 mm Hg. These data may predict the optimal environmental temperature range for a given s pecies with respect to gas transport. We have also described the inter play of temperature and protons in the modulation of oxygen binding fo r one species, the squid Todarodes sagitatus. Within the physiological pH range, the concentration of protons affects mainly the high-affini ty state of the molecule without significantly affecting the low-affin ity state. The shape of the oxygen-binding curve shows a strong temper ature-dependence, since the overall heat of the binding of oxygen to t he low-affinity state of the molecule is strongly exothermic and that to the high-affinity stale is very close to zero. The results outline the intramolecular compromise that optimizes oxygen loading and unload ing through the interplay of temperature and protons under the various environmental conditions experienced by these animals.