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

We investigated divalent cation and anaerobic end-product concentrations and the interactive effects of these substances and pH on haemocyanin oxygen-binding (Hc-O(2)) 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 [Ca(2+)], [Mg(2+)], pH and O(2)-binding properties of the native haemolymph. The haemolymph showed a low Hc-O(2) affinity, a large reverse Bohr effect and marked cooperativity. Dialysis increased Hc-O(2) affinity, obliterated cooperativity and decreased the pH-sensitivity of O(2) binding. Replacing Mg(2+) and Ca(2+) restored the native O(2)-binding properties and the reverse Bohr shift. L- and D-lactate exerted minor modulatory effects on O(2)-affinity. At in vivo concentrations of Mg(2+) and Ca(2+), the cooperativity is dependent largely on Mg(2+), which modulates the O(2) 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 O(2) delivery to the tissues are not a priority but are consistent with the provision of a large O(2) reserve for facultatively anaerobic tissues during internal hypoxia associated with clamping to the substratum.