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The Journal of Experimental Biology 206, 2693-2702 (2003)
doi: 10.1242/jeb.00475

Hemoglobin function in deep-sea and hydrothermal-vent endemic fish: Symenchelis parasitica (Anguillidae) and Thermarces cerberus (Zoarcidae)

Roy E. Weber^1,*, Stephane Hourdez², Francis Knowles³ and Francois Lallier⁴

¹ Department of Zoophysiology, C.F. Møllers Alle, Building 131, University of Aarhus, DK 8000 Aarhus C, Denmark
² Department of Biology, Pennsylvania State University, University Park, PA 16802, USA
³ Department of Chemistry, University of California at San Diego, La Jolla, CA 92093, USA
⁴ Station Biologique de Roscoff, UPMC-CNRS-INSU, 29682 Roscoff Cedex, France

^* Author for correspondence (e-mail: roy.weber{at}biology.au.dk)

Accepted 6 May 2003

Deep-sea hydrothermal vents probably provide the harshest physico-chemical conditions confronting metazoan animals in nature. Given the absence of information on hemoglobin (Hb) function in hydrothermal-vent vertebrates, and the complex molecular and functional adaptations observed in hydrothermal-vent invertebrates, we investigated the oxygenation reactions of Hbs from the vent-endemic zoarcid Thermarces cerberus and the deep-sea anguillid Symenchelis parasitica from adjacent habitats.

Electrophoretically cathodic and anodic isoHbs from S. parasitica exhibit radical differences in O₂ affinity and pH and organic phosphate (ATP) sensitivities, reflecting a division of labor as in other `class II' fish that express both Hb types. Remarkably, the cathodic Hb (I) lacks chloride sensitivity, and the anodic Hb (II) shows anticooperativity near half-saturation at low temperature. T. cerberus isoHbs exhibit similar affinities and pH sensitivities (`class I' pattern) but much higher O₂ affinities than those observed in Hbs of the temperate, shallow-water zoarcid Zoarces viviparus, which, unless compensated, reveals markedly higher blood O₂ affinities in the former species. The temperature sensitivity of O₂ binding to T. cerberus Hbs and the anodic S. parasitica Hb, which have normal Bohr effects, is decreased by endothermic proton dissociation, which reduces the effects of ambient temperature variations on O₂ affinity. In the cathodic S. parasitica Hb, similar reduction appears to be associated with endothermic conformational changes that accompany the oxygenation reaction.

Key words: hemoglobin, oxygen binding, enthalpy, deep-sea fish, hydrothermal vent, anguillid, zoarcid, Thermarces cerberus, Symenchelis parasitica

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