Larsen Christina, Malte Hans, Weber Roy E
Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Building 131, 8000 Aarhus, Denmark.
J Biol Chem. 2003 Aug 15;278(33):30741-7. doi: 10.1074/jbc.M301930200. Epub 2003 May 27.
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 degrees C, respectively) and Hb V (P50 = 1.5 and 2.5 torr at 10 and 26 degrees C, respectively). In the presence of this effector P50 decreases with increasing temperature in both components (P50 at 10 and 26 degrees 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.
恒温金枪鱼和鼠鲨的趋同进化十分独特。它们由热交换器调节的恒温现象代表了与这一特定特征相关的进化压力的一个有趣例子。为了评估恒温对气体运输的影响以及血红蛋白（Hb）可能发挥的作用，我们研究了温度对鼠鲨（Lamna nasus）纯化的异血红蛋白组分V和III氧平衡的影响。在没有ATP的情况下，温度对氧亲和力的影响在Hb III（10℃和26℃时P50分别为0.9和2.2托）和Hb V（10℃和26℃时P50分别为1.5和2.5托）中都是正常的。在这种效应物存在的情况下，两种组分的P50都随温度升高而降低（10℃和26℃时Hb III的P50分别为9.9和8.4托，Hb V的P50分别为9.6和7.4托）。ATP存在时的这种反向温度效应将通过降低血管间的氧分压梯度来降低氧从动脉血向静脉血流失的风险。这种反向温度效应背后的机制类似于在恒温硬骨鱼蓝鳍金枪鱼（Thunnus thynnus）中发现的机制，从而证明了进一步的趋同进化。
