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The Journal of Experimental Biology 205, 253-263 (2002)
© 2002 The Company of Biologists Limited

The archaeogastropod mollusc Haliotis iris: tissue and blood metabolites and allosteric regulation of haemocyanin function

Jane W. Behrens^1,3, John P. Elias^2,3, H. Harry Taylor³ and Roy E. Weber^1,*

¹ Department of Zoophysiology, Institute Biological Sciences, University of Aarhus, DK 8000 Aarhus, Denmark,
² School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia and
³ Department of Zoology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand

*Author for correspondence (e-mail: roy.weber{at}biology.au.dk)

Accepted 30 October 2001

We investigated divalent cation and anaerobic end-product concentrations and the interactive effects of these substances and pH on haemocyanin oxygen-binding (Hc-O₂) in the New Zealand abalone Haliotis iris. During 24 h of environmental hypoxia (emersion), D-lactate and tauropine accumulated in the foot and shell adductor muscles and in the haemolymph of the aorta, the pedal sinus and adductor muscle lacunae, whereas L-lactate was not detected. Intramuscular and haemolymph D-lactate concentrations were similar, but tauropine accumulated to much higher levels in muscle tissues. Repeated disturbance and short-term exposure to air over 3 h induced no accumulation of D- or L-lactate and no change in [Ca²⁺], [Mg²⁺], pH and O₂-binding properties of the native haemolymph.

The haemolymph showed a low Hc-O₂ affinity, a large reverse Bohr effect and marked cooperativity. Dialysis increased Hc-O₂ affinity, obliterated cooperativity and decreased the pH-sensitivity of O₂ binding. Replacing Mg²⁺ and Ca²⁺ restored the native O₂-binding properties and the reverse Bohr shift. L- and D-lactate exerted minor modulatory effects on O₂-affinity. At in vivo concentrations of Mg²⁺ and Ca²⁺, the cooperativity is dependent largely on Mg²⁺, which modulates the O₂ association equilibrium constants of both the high-affinity (K_R) and the low-affinity (K_T) states (increasing and decreasing, respectively). This allosteric mechanism contrasts with that encountered in other haemocyanins and haemoglobins. The functional properties of H. iris haemocyanin suggest that high rates of O₂ delivery to the tissues are not a priority but are consistent with the provision of a large O₂ reserve for facultatively anaerobic tissues during internal hypoxia associated with clamping to the substratum.

Key words: gastropod, mollusc, Haliotis iris, haemocyanin, oxygen-binding, Bohr effect, ionic effector, association constant, calcium, magnesium, lactate, tauropine.

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