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

Abstract

SUMMARYDeep-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. parasiticaexhibit 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. cerberusHbs 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.