Properties of trout HbI in water and ligand linked binding of Na⁺

Hemoglobin Allostery: New Views on Old Players

“…2), and it is not affected by DPG, ATP, IHP and PLP 14 ; the effect of Cl − 0.3 M is to shift p 50 from 12-13 mmHg (isoionic, pH 7.72) to 14-15 mmHg. 13 derivative (see Fig. 1b), and particularly significant is the finding that, in both subunits, the distance between the distal His and the bound CO is increased compared to HbA (3.0-3.2 Å versus 2.8-2.9 Å, respectively).…”

“…8,19,31 On the other hand, O 2 binding in T-HbI is cooperative yet the Hill plot and ligand affinity are totally independent of pH and solvent composition including organic phosphates. 9,10,13,14 This peculiarity, and particularly the absence of the Bohr effect, was taken as the paradigmatic case of molecular adaptation to physiological requirements; Brunori proposed that fastswimming fishes need an O 2 carrier that is cooperative but pH independent to allow O 2 delivery even when blood pH drops significantly due to strenuous swimming for survival. 9 The absence of heterotropic effects in T-HbI proved to be the best independent evidence for the role of a limited number of wellidentified amino acids in HbA, which were proposed by Perutz 2,19,32,33 to be involved in the Bohr effect and in the binding of DPG.…”

“…12 HbA and T-HbI are ideal for the purpose being "very similar yet very different". Apart from cooperative O 2 binding even under isoionic conditions, 13 T-HbI is quite peculiar since O 2 affinity and cooperativity are totally independent of classical heterotropic effectors given that there is no Bohr effect, no effect of organic phosphates [2,3-di-phosphoglycerate (DPG), adenosine triphosphate (ATP), inositol hexaphosphate (IHP) and pyridoxal 5′-phosphate (PLP)] and only a negligible effect of chloride, orthophosphate and Na + that increases p 1/2 from 12-13 mmHg to 14-15 mmHg at 0.2-0.3 M. [13][14][15] There is no kinetic, equilibrium and spectroscopic evidence for αβ subunit heterogeneity, and the tetramer is approximately 100fold more stable than liganded HbA. 16,17 In a nutshell, T-HbI has none of the classical heterotropic control properties typical of most other tetrameric hemoglobins, such as the Bohr effect and the DPG control, yet is cooperative in O 2 and CO binding.…”

Dynamics of the quaternary conformational change in trout hemoglobin

“…Another useful characteristic of trout Hb I is that it is a more stable molecule than human hemoglobin. The tetramer-dimer dissociation constant for the fully liganded molecule has only been approximately measured (Brunori et al, 1973), but kinetic studies on dilute solutions show that no dimers are present, indicating that it must be less than 0.1 /uM (Giardina et al, 1973;Airoldi et al, 1981). The molecule is also stable at temperatures as high as 65 °C for more than 1 h, permitting kinetic studies to be carried out over an extremely wide range of temperatures (Brunori et al, 1980(Brunori et al, , 1982.…”

Modulation of Allosteric Control and Evolution of Hemoglobin

“…L 0 , K R and K T yield a ligand binding curve that is cooperative over a fairly restricted range of O 2 concentration ( Figure 1 A). As outlined above, this tetrameric Hb is the perfect case of an allosteric system characterized by cooperative ligand binding, but devoid of heterotropic effects; the binding curve being independent of pH, organic phosphates and temperature, only an effect of Na + on affinity was discovered by Airoldi et al [ 47 ]. Moreover, it displays an unusual temperature stability (up to >70 °C), as well as -tetramer stability.…”