» Articles » PMID: 11604545

High and Low Oxygen Affinity Conformations of T State Hemoglobin

Overview
Journal Protein Sci
Specialty Biochemistry
Date 2001 Oct 18
PMID 11604545
Citations 27
Authors
Affiliations
Soon will be listed here.
Abstract

To understand the interplay between tertiary and quaternary transitions associated with hemoglobin function and regulation, oxygen binding curves were obtained for hemoglobin A fixed in the T quaternary state by encapsulation in wet porous silica gels. At pH 7.0 and 15 degrees C, the oxygen pressure at half saturation (p50) was measured to be 12.4 +/- 0.2 and 139 +/- 4 torr for hemoglobin gels prepared in the absence and presence of the strong allosteric effectors inositol hexaphosphate and bezafibrate, respectively. Both values are in excellent agreement with those found for the binding of the first oxygen to hemoglobin in solution under similar experimental conditions. The corresponding Hill coefficients of hemoglobin gels were 0.94 +/- 0.02 and 0.93 +/- 0.03, indicating, in the frame of the Monod, Wyman, and Changeux model, that high and low oxygen-affinity tertiary T-state conformations have been isolated in a pure form. The values, slightly lower than unity, reflect the different oxygen affinity of alpha- and beta-hemes. Significantly, hemoglobin encapsulated in the presence of the weak effector phosphate led to gels that show intermediate oxygen affinity and Hill coefficients of 0.7 to 0.8. The heterogeneous oxygen binding results from the presence of a mixture of the high and low oxygen-affinity T states. The Bohr effect was measured for hemoglobin gels containing the pure conformations and found to be more pronounced for the high-affinity T state and almost absent for the low-affinity T state. These findings indicate that the functional properties of the T quaternary state result from the contribution of two distinct, interconverting conformations, characterized by a 10-fold difference in oxygen affinity and a different extent of tertiary Bohr effect. The very small degree of T-state cooperativity observed in solution and in the crystalline state might arise from a ligand-induced perturbation of the distribution between the high- and low-affinity T-state conformations.

Citing Articles

Zuclopenthixol Induced Ischemic Priapism: Case Report and Review of Literature.

Mansour E, Danaf S, Ghousayneh D, Assaf G, Ghantous I, El-Khoury F J Family Reprod Health. 2023; 17(2):109-112.

PMID: 37547784 PMC: 10397527. DOI: 10.18502/jfrh.v17i2.12875.


Structural Basis of Sequential and Concerted Cooperativity.

Morea V, Angelucci F, Tame J, Di Cera E, Bellelli A Biomolecules. 2022; 12(11).

PMID: 36359000 PMC: 9687781. DOI: 10.3390/biom12111651.


Direct observation of conformational population shifts in crystalline human hemoglobin.

Shibayama N, Ohki M, Tame J, Park S J Biol Chem. 2017; 292(44):18258-18269.

PMID: 28931607 PMC: 5672048. DOI: 10.1074/jbc.M117.781146.


An Origin of Cooperative Oxygen Binding of Human Adult Hemoglobin: Different Roles of the α and β Subunits in the α2β2 Tetramer.

Nagatomo S, Nagai Y, Aki Y, Sakurai H, Imai K, Mizusawa N PLoS One. 2015; 10(8):e0135080.

PMID: 26244770 PMC: 4526547. DOI: 10.1371/journal.pone.0135080.


Experiments on Hemoglobin in Single Crystals and Silica Gels Distinguish among Allosteric Models.

Henry E, Mozzarelli A, Viappiani C, Abbruzzetti S, Bettati S, Ronda L Biophys J. 2015; 109(6):1264-72.

PMID: 26038112 PMC: 4576146. DOI: 10.1016/j.bpj.2015.04.037.


References
1.
Perutz M . Mechanisms of cooperativity and allosteric regulation in proteins. Q Rev Biophys. 1989; 22(2):139-237. DOI: 10.1017/s0033583500003826. View

2.
DVORAK J, Stotler W . A controlled-environment culture system for high resolution light microscopy. Exp Cell Res. 1971; 68(1):144-8. DOI: 10.1016/0014-4827(71)90596-9. View

3.
Perrella M . Understanding mechanisms in a cooperative protein: the CO ligation intermediates of hemoglobin. Biophys Chem. 1999; 81(3):157-78. DOI: 10.1016/s0301-4622(99)00093-9. View

4.
Baldwin J, Chothia C . Haemoglobin: the structural changes related to ligand binding and its allosteric mechanism. J Mol Biol. 1979; 129(2):175-220. DOI: 10.1016/0022-2836(79)90277-8. View

5.
Eaton W, Henry E, Hofrichter J, Mozzarelli A . Is cooperative oxygen binding by hemoglobin really understood?. Nat Struct Biol. 1999; 6(4):351-8. DOI: 10.1038/7586. View