Temperature Sensitivity of Molluscan and Arthropod Hemocyanins

¹ Department of Biology, University of San Diego, Akala Park, San Diego, California 92110
² Department of Biology, College of William and Mary, Williamsburg, Virginia 23185

The temperature sensitivity of hemocyaninoxygen affinity and cooperativity was measured at 5, 15, 25, and 35°C in a variety of manine molluscs and arthropods from different thermal environments. These environments included a subtidal habitat in which the temperature is generally less than 15°C and the diurnal temperature variation is small, and an intertidal habitat in which the temperature varies more than 30°C. The temperature sensitivity of P₅₀ showed considerable variation (H = 0 to H = -67 kJ/mol) depending on species and experimental temperatures. Sensitivity generally decreased as temperature increased. In several species temperature sensitivity was either absent or greatly reduced above 15°C. The horseshoe crab Limulus polyphemus showed a minimum temperature sensitivity between 15 and 25°C but higher sensitivity above and below this range. The hypothesis that a greater interaction between hemocyanin molecules and calcium ions at high temperatures offsets the temperature effect, resulting in a pigment less sensitive to temperature, was supported in an experiment where calcium ions were removed. Finally, deipidation of hemocyanin resulted in little or no change in oxygen affinity at all temperatures investigated.

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