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Ole Brix Astrid Bårdgard Svein Mathisen Nicholas Tyler Matti Nuutinen Sarveriò G. Condo Bruno Giardina 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,159(6):655-660
Summary The oxygen binding of whole blood from humans and two arctic mammals, reindeer and muskox, has been studied as a function of carbon dioxide and temperature. All bloods display a marked Bohr effect with Bohr coefficients in the range –0.44––0.73. The Bohr effect is more pronounced at 20°C. The temperature sensitivity of reindeer and muskox blood expressed by the apparent heat of oxygenation, H, is almost three times lower than that of human HbA under the same experimental conditions. This thermodynamic difference gives special benefits to arctic mammals with large heterothermy by safeguarding oxygen unloading at very low ambient temperatures. 相似文献
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R. J. Feuerlein R. E. Weber 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,165(8):597-606
Allosteric effects of erythrocytic NTP and proton concentrations on cathodic eel Hb were investigated by precise measurement of Hb-O2 equilibria (including extreme saturation values) and analysis in terms of the MWC two-state model and the Adair four-step oxygenation theory. Stripped cathodic Hb shows a reverse Bohr effect and high sensitivities to ATP and GTP that extend to high pH values (>8.5). A decrease in pH raises K
T and lowers the allosteric constant L; compared to opposite effects in normal Bohr effect Hbs. Phosphates even at low concentrations (GTP/Hb=0.5) annihilate the reverse Bohr effect. GTP exerts a reater effect than ATP due to greater changes in K
T and L, and NTP slightly reduces K
R. In the absence of NTP, about 1.1 protons are released on deoxygenation at pH 8.15 (where most protons are released), indicating a pK value of the reverse Bohr group of approximately 8.2 (higher in oxy-Hb and lower in deoxy-Hb). The pH and NTP dependence of the Adair association constants and calculated fractional populations of Hb molecules in different oxygenation stages show that NTP effectors stabilise the T structure and postpone the T-R transition, whereas protons in the absence of NTP have the opposite effect. A molecular mechanism for the reverse Bohr effect is suggested.Abbreviations
DPG
2,3 diphosphoglycerate
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EPLC
fast protein liquid chromatography
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Hb
hemoglobin
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HEPES
N-2-hydroxymethyl-piperazine-N-2-ethanesulfonic acid
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K
T and K
R O2
association equilibrium constants of Hb in the deoxy- and oxy-states, respectively
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k
1, k
2, k
3 and k
4
Adair affinity constants for binding of the four O2 molecules to Hb
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L
allosteric constant
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NTP
nucleoside triphosphate
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P
m
medium O2 pressure
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n
50
Hill's cooperativity coefficient at P
50
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P
50
half-satutarion O2 tension
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TRIS
tris(hydroxymethyl)aminomethane 相似文献
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