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Journal of Experimental Biology 86,19-37 (1980)
Published by Company of Biologists 1980

Haemoglobin-Oxygen Binding Properties in the Blood of Xenopus Laevis, with Special Reference to the Influences of Aestivation and of Temperature and Salinity Acclimation

ALFRED JOKUMSEN ¹ and ROY E. WEBER ²

¹ Department of Zoophysiology, University of Aarhus DK-Sooo Aarhus C., Denmark
² Institute of Biology, University of Odense DK-5230 Odense M., Denmark

The oxygen equilibrium properties of blood and of solutions of haemoglobin from Xenopus laevis are reported. At pH 7.6 the oxygen affinity of the blood, expressed as half saturation oxygen tension (P₅₀) amounts to 27.0 mm and 13.7 mmHg (3.60 and 1.83 kPa) when measured at 25 and 10 °C, while the Bohr factor (log P₅₀/pH) was -0.40, and the Hill's cooperativity coefficient, n, averaged 2.1. These data reflect an overall heat of oxygenation, H, of -7.9 kcal. mol^-1, which decreased to -6.3 kcal. mol^-1 when the live animals were acclimated to each measuring temperature. Xenopus blood showed a high O₂ capacity (15 vol.%) compared to that of other amphibians.

Acclimation to water of increased salinity (12%₀), and aestivation, raised blood O₂ affinity; at 25 °C and pH 7.6, P₅₀ decreased to 21.1 and 25.2 mmHg (2.81 and 3.36 kPa), respectively. These changes were concomitant with increases in the blood levels of urea. In contrast to NaCl and ATP, urea increased O₂ affinity of the purified haemoglobin, suggesting that oxygenationlinked binding to haemoglobin is involved in the modulations of the blood O₂ affinity during aestivation and acclimation to salt water.

Xenopus haemoglobin consists of two components. The major component is electrophoretically anodal, and has O₂ binding properties similar to those of the haemolysate; the minor component is cathodal, and shows extremely low P₅₀, pH sensitivity and cooperativity.

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