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J. Biol. Chem., Vol. 278, Issue 33, 30741-30747, August 15, 2003

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ATP-induced Reverse Temperature Effect in Isohemoglobins from the Endothermic Porbeagle Shark (Lamna nasus)^*

Christina Larsen, Hans Malte  and Roy E. Weber

From the Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Building 131, 8000 Aarhus, Denmark

The evolutionary convergence of endothermic tunas and lamnid sharks is unique. Their heat exchanger-mediated endothermy represents an interesting example of the evolutionary pressure associated with this specific characteristic. To assess the implications of endothermy for gas transport and the possible contribution of hemoglobin (Hb), we investigated the effect of temperature on the oxygen equilibria of purified isohemoglobin components V and III from the porbeagle shark (Lamna nasus). In the absence of ATP the effect of temperature on oxygen affinity is normal in both Hb III (P₅₀ = 0.9 and 2.2 torr at 10 and 26 °C, respectively) and Hb V (P₅₀ = 1.5 and 2.5 torr at 10 and 26 °C, respectively). In the presence of this effector P₅₀ decreases with increasing temperature in both components (P₅₀ at 10 and 26 °C = 9.9 and 8.4 torr (Hb III), respectively, and 9.6 and 7.4 torr (Hb V), respectively. The reverse temperature effect in the presence of ATP will reduce the risk of oxygen loss from the arterial to the venous blood by lowering the oxygen tension gradient between the blood vessels. The mechanism behind the reverse temperature effect resembles that found in the bluefin tuna (Thunnus thynnus), an endothermic teleost, thus evidencing further convergent evolution.

Received for publication, February 24, 2003 , and in revised form, May 6, 2003.

^* This work was supported by the Oticon Foundation and the Danish Natural Science Research Council. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 45-89422596; Fax: 45-86194186; E-mail: Hans.Malte{at}biology.au.dk.

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