title: Macromolecular isoforms of Daphnia magna haemoglobin.
abstract: The haemoglobin (Hb) of Daphnia magna acclimated to different oxygen conditions was sampled, and in its natively assembled state it was separated by chromatofocusing. The Hb isoforms were analysed for their subunit composition under denaturating conditions by two-dimensional gel electrophoresis. The Hb system is suggested to consist of three predominant Hb aggregates, which are characterised by a specific subunit composition and synthesised in response to different ambient oxygen conditions. In normoxia, a dominant Hb aggregate (DmHbI) with a pI of 4.4-4.6 was composed of subunits B, C, E, F and G. In severe hypoxia, a different dominant Hb isoform (DmHbIII) with a pI of 5.7-5.9 was composed of subunits A, B, C, D, E and F. Further analyses in moderate hypoxia provided evidence for a third Hb isoform (DmHbII) composed of subunits B, C, D, E and F. Sequence alignment and homology modelling of the tertiary structure of the D. magna Hb domains 1 and 2 revealed functionally relevant substitutions of amino acid residues at positions B10, E7 and E11, which determine the functional properties of D. magna haemoglobin in terms of haem contact, oxygen binding and affinity. Both domains are predicted to possess the common haemoglobin fold, but helices C and D are not properly formed, and helix G is interrupted by a short coil.
authors.affiliation: Institut für Zoophysiologie, Westfälische Wilhelms-Universität, Hindenburgplatz 55, D-48143 Münster, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Lamkemeyer
authors.forename: Rüdiger J
authors.initials: RJ
authors.lastname: Paul
authors.forename: Walter
authors.initials: W
authors.lastname: Stöcker
authors.forename: Irene
authors.initials: I
authors.lastname: Yiallouros
authors.forename: Bettina
authors.initials: B
authors.lastname: Zeis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003621:Daphnia; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000235:genetics; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D006454:Hemoglobins; D046912:Multiprotein Complexes; D020033:Protein Isoforms