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Journal of Experimental Biology 150,407-424 (1990)
Published by Company of Biologists 1990

An Analysis of the Effects of pH on Oxygen Binding by Squid (Illex Illecebrosus, Loligo Pealei) Haemocyanin

HANS-OTTO PÖRTNER 1

1 Department of Biology, Dalhousie University Halifax, NS, Canada B0P 1X0; Institut für Zoologie, Lehrstuhl für Tierphysiologie, Heinrich-Heine-Universitat Düsseldorf, D-4000 Düsseldorf, FRG

Address for reprint requests.

The in vitro oxygen-binding characteristics of haemocyanin were investigated in whole blood of two species of pelagic squid, Illex illecebrosus and Loligo pealei. pH-independent Haldane coefficients ({Delta}HCO3-/{Delta}HcyO2) (where HcyO2 is haemocyanin-bound oxygen) slightly smaller than —1 were found in both species. Oxygen-linked CO2 binding was not present. Buffer values ranged between 5 and 5.8 m mol l-1pH unit-1. For further analyses a pH/saturation diagram was selected to show the effect of pH on oxygen binding at constant POO2 in a continuous plot. The slopes of the resulting oxygen isobars ({Delta}HcyO2/{Delta}pH or {Delta}S/{Delta}pH) (where S is oxygen saturation) depend on pH. The diagram allows evaluation of both the Bohr coefficients ({Delta}logP50/{Delta}pH) and the Hill coefficients (n50) at specific pH values. It provides an integrated illustration of the importance of the Bohr effect and cooperativity for oxygen binding.

In accordance with Wyman's linkage equation, Bohr and Haldane coefficients are found to be identical. Both are pH-independent between pH7 and 8. The changing slopes of the oxygen isobars are likely to reflect changes in cooperativity with pH. Maximum values of n50 coincide with maximum steepness of the oxygen isobars in the physiological range of pH and POO2. Assuming that the haemocyanin acts as a buffer for venous POO2, this maximum in pH sensitivity and its decrease in the higher and lower pH ranges are discussed in the light of the maintenance of pigment function in vivo.

Key words: squid haemocyanin, cephalopod, Bohr effect, Haldane effect, cooperativity, pH/saturation diagram, oxygenation, deoxygenation, lllexUlecebrosus, Loligo pealei, Octopus.

Accepted on January 5, 1990




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© The Company of Biologists Ltd 1990