title: Interspecific variation and plasticity in hemoglobin nitrite reductase activity and its correlation with oxygen affinity in vertebrates.
abstract: Deoxygenated hemoglobin (Hb) is a nitrite reductase that reduces naturally occurring nitrite to nitric oxide (NO), supplying physiological relevant NO under hypoxic conditions. The nitrite reductase activity is modulated by the allosteric equilibrium between the R and T structures of Hb that also determines oxygen affinity. In the present study we investigated nitrite reductase activity and O2affinity in Hbs from ten different vertebrate species under identical conditions to disclose interspecific variations and allow an extended test for a correlation between the rate constant for nitrite reduction and O2affinity. We also tested plastic changes in Hb properties via addition of T-structure-stabilizing organic phosphates (ATP and GTP). The decay in deoxyHb during its reaction with nitrite was exponential-like in ectotherms (Atlantic hagfish, carp, crucian carp, brown trout, rainbow trout, cane toad, Indian python and red-eared slider turtle), while it was sigmoid in mammals (harbor porpoise and rabbit). Typically, hypoxia-tolerant species showed a faster reaction than intolerant species. Addition of ATP and GTP decreased O2affinity and slowed the rate of nitrite reduction in a concentration-dependent manner. The initial second order rate constant of the deoxyHb-mediated nitrite reduction showed a strong curvilinear correlation with oxygen affinity among all ectothermic vertebrates, and the relationship also applied to plastic variations of Hb properties via organic phosphates. The relationship predicts high nitrite reductase activity in hypoxic tolerant species with high Hb-O2affinity and reveals that the decrease in erythrocyte ATP and/or GTP during acclimation to hypoxia in ectotherms increases the erythrocyte NO generating capacity.
authors.affiliation: Department of Biology, University of Southern Denmark, DK-5230, Odense M, Denmark. Electronic address: fbj@biology.sdu.dk.
authors.forename: Frank B
authors.initials: FB
authors.lastname: Jensen
authors.affiliation: Department of Biology, University of Southern Denmark, DK-5230, Odense M, Denmark.
authors.forename: Rasmus A H
authors.initials: RA
authors.lastname: Kolind
authors.affiliation: Department of Biology, University of Southern Denmark, DK-5230, Odense M, Denmark.
authors.forename: Natashia S
authors.initials: NS
authors.lastname: Jensen
authors.affiliation: Department of Biology, University of Southern Denmark, DK-5230, Odense M, Denmark.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Montesanti
authors.affiliation: Department of Bioscience, Aarhus University, DK-8000 AarhusC, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wang
mesh_terms: D000064:Acclimatization; D000255:Adenosine Triphosphate / Q000378:metabolism; D029845:Amphibian Proteins / Q000378:metabolism*; D000818:Animals; D001001:Anura / Q000502:physiology; D017821:Boidae / Q000502:physiology; D015687:Cell Hypoxia; D029941:Fish Proteins / Q000378:metabolism*; D005399:Fishes; D006160:Guanosine Triphosphate / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism*; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism; D009572:Nitrite Reductases / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D050741:Phocoena; D011817:Rabbits; D030162:Reptilian Proteins / Q000378:metabolism*; D013045:Species Specificity; D014426:Turtles / Q000502:physiology
chemical_list: D029845:Amphibian Proteins; D029941:Fish Proteins; D006454:Hemoglobins; D009573:Nitrites; D030162:Reptilian Proteins; D009569:Nitric Oxide; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; C100003:deoxyhemoglobin; D009572:Nitrite Reductases; D010100:Oxygen
keywords: Hemoglobin; Hypoxia; NO synthase; Nitric oxide; Nitrite reduction; Organic phosphates; Oxygen affinity; Reaction kinetics