title: Oxygen binding properties of non-mammalian nerve globins.
abstract: Oxygen-binding globins occur in the nervous systems of both invertebrates and vertebrates. While the function of invertebrate nerve haemoglobins as oxygen stores that extend neural excitability under hypoxia has been convincingly demonstrated, the physiological role of vertebrate neuroglobins is less well understood. Here we provide a detailed analysis of the oxygenation characteristics of nerve haemoglobins from an annelid (Aphrodite aculeata), a nemertean (Cerebratulus lacteus) and a bivalve (Spisula solidissima) and of neuroglobin from zebrafish (Danio rerio). The functional differences have been related to haem coordination: the haem is pentacoordinate (as in human haemoglobin and myoglobin) in A. aculeata and C. lacteus nerve haemoglobins and hexacoordinate in S. solidissima nerve haemoglobin and D. rerio neuroglobin. Whereas pentacoordinate nerve globins lacked Bohr effects at all temperatures investigated and exhibited large enthalpies of oxygenation, the hexacoordinate globins showed reverse Bohr effects (at least at low temperature) and approximately twofold lower oxygenation enthalpies. Only S. solidissima nerve haemoglobin showed apparent cooperativity in oxygen binding, suggesting deoxygenation-linked self-association of the monomeric proteins. These results demonstrate a remarkable diversity in oxygenation characteristics of vertebrate and invertebrate nerve haemoglobins that clearly reflect distinct physiological roles.
authors.affiliation: Zoophysiology, Institute of Biological Sciences, University of Aarhus, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Hundahl
authors.forename: Angela
authors.initials: A
authors.lastname: Fago
authors.forename: Sylvia
authors.initials: S
authors.lastname: Dewilde
authors.forename: Luc
authors.initials: L
authors.lastname: Moens
authors.forename: Tom
authors.initials: T
authors.lastname: Hankeln
authors.forename: Thorsten
authors.initials: T
authors.lastname: Burmester
authors.forename: Roy E
authors.initials: RE
authors.lastname: Weber
mesh_terms: D000818:Animals; D000845:Annelida; D017124:Conserved Sequence; D005914:Globins / Q000378:metabolism*; D006454:Hemoglobins; D006863:Hydrogen-Ion Concentration; D009417:Nerve Tissue / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D000078787:Neuroglobin; D010100:Oxygen / Q000378:metabolism*; D013696:Temperature; D015027:Zebrafish
chemical_list: D006454:Hemoglobins; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D005914:Globins; D010100:Oxygen