The Functionally Distinct Hemoglobins of the Arctic Spotted Wolffish Anarhichas minor

Abstract The Arctic fish Anarhichas minor, a benthic sedentary species, displays high hemoglobin multiplicity. The three major hemoglobins (Hb 1, Hb 2, and Hb 3) show important functional differences in pH and organophosphate regulation, subunit cooperativity, and response of oxygen binding to temperature. Hb 1 and Hb 2 display a low, effector-enhanced Bohr effect and no Root effect. In contrast, Hb 3 displays pronounced Bohr and Root effects, accompanied by strong organophosphate regulation. Hb 1 has the β (β1) chain in common with Hb 2; Hb 3 and Hb 2 share the α (α2) chain. The amino acid sequences have been established. Several substitutions in crucial positions were observed, such as Cys in place of C-terminal His in the β1 chain of Hb 1 and Hb 2. In Hb 3, Val E11 of the β2 chain is replaced by Ile. Homology modeling revealed an unusual structure of the Hb 3 binding site of inositol hexakisphoshate. Phylogenetic analysis indicated that only Hb 2 displays higher overall similarity with the major Antarctic hemoglobins. The oxygen transport system ofA. minor differs remarkably from those of Antarctic Notothenioidei, indicating distinct evolutionary pathways in the regulatory mechanisms of the fish respiratory system in the two polar environments.