ISSN:
1432-136X
Keywords:
Cathodic components
;
Hemoglobin
;
Oxygen-binding
;
Eel, Anguilla
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00301127
