1P034 Novel Mechanisms of pH sensitivity in tuna hemoglobin : a structural explanation of the Root effect

Yokoyama, T.; Chong, Khoon Tee; Miyazaki, Gentaro; Morimoto, H.; Shih, Daniel Tzu-Bi; Unzai, Satoru; Tame, J.R.H.; Sy, Park

doi:10.2142/biophys.44.s38_2

Cited by 18 publications

(62 citation statements)

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“…Based on the reported heats of protonation of imidazole groups of ~24kJmol -1 (Atha et al, 1974) and 16-37kJmol -1 (Bhattacharya and Lecomte, 1997)], the overall enthalpy of proton release of ~42kJmol -1 O 2 observed in blue marlin at pH7.4 (above) indicates ionization of at least two imidazoles per O 2 molecule bound (eight per tetrameric Hb molecule). In this regard, however, it should be noted that Xray crystal analysis of tuna Hb has identified a mechanism of pHdependent control of ligand affinity that includes 'novel' proton binding sites (at His-60, His-69/Asp-72 and Asp- 1 96/Asp- 2 101) (Yokoyama et al, 2004) that may have different heats of ionization. Thus, the identification of the 'Bohr-proton' binding residues implicated in billfish Hbs must await elucidation of the structure of billfish Hbs.…”

Section: Atp Sensitivitymentioning

confidence: 99%

“…Indeed, in cold-tolerant ruminants, low temperature sensitivity of O 2 affinity correlates with a heightened oxygenation-linked, endothermic dissociation of chloride ions compared with that in other mammalian Hbs (Coletta et al, 1994;De Rosa et al, 2004). By contrast, the temperature insensitivity of tuna (Thunnus thynnus) Hb (Rossi-Fanelli et al, 1960) arises through a pH-dependent control of O 2 affinity (Yokoyama et al, 2004) associated with large Bohr effects (allosteric release of many protons upon oxygenation) (Jensen, 2001). In tuna Hb component I, the temperature insensitivity at half-saturation correlates with a normal temperature sensitivity below P 50 and a reversed sensitivity above P 50 (Ikeda-Saito et al, 1983) indicating that Bohr proton dissociation occurs predominantly at high O 2 saturations -as also applies to the Hbs of tench (Jensen, 1986), rainbow trout (Brauner et al, 1996) and yellowfin and skipjack tunas (Lowe et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

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ATP-induced temperature independence of hemoglobin–O2 affinity in heterothermic billfish

Weber

Campbell

Fago

et al. 2010

Journal of Experimental Biology

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SUMMARYThe inverse relationship between temperature and hemoglobin-O 2 affinity resulting from the exothermic nature of heme oxygenation favors O 2 unloading from blood to warm, metabolically active tissues. However, this temperature sensitivity is maladaptive, and commonly countered in regional heterotherms, where it may hamper unloading (e.g. in cold extremities of arctic mammals) or increase the diffusive arterio-venous short-circuiting of O 2 (e.g. in counter-current heat exchangers of warm swimming muscles of tuna). We hypothesized analogous blood specializations in heterothermic billfish, whose warm eyes and brains increase the temporal resolution of vision, and measured hemoglobin-O 2 binding properties in three species over a wide pH range, at two temperatures, and in the absence and presence of the major red cell effector, ATP, permitting detailed assessment of overall oxygenation enthalpies (⌬HЈ) and contributions from oxygenation-linked proton and ATP dissociation. . Thus in addition to allosterically modulating hemoglobin-O 2 affinity, ATP diminishes its temperature sensitivity, reducing deleterious arterio-venous short-circuiting of oxygen in the cranial billfish heat exchangers. The mechanism underlying this reduction in oxygenation enthalpy differs fundamentally from that in tuna, supporting independent evolution of this trait in these scombroid lineages.

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Section: Atp Sensitivitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

ATP-induced temperature independence of hemoglobin–O2 affinity in heterothermic billfish

Weber

Campbell

Fago

et al. 2010

Journal of Experimental Biology

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“…Thus, as in the Bohr effect of human Hb, the C-terminal histidine of the ␤-chains may be responsible for about 50% of the total Root effect in Hb of common carp (Cyprinus carpio) (Parkhurst et al, 1983). On the other hand, structural studies on Hbs of the Antarctic fishes Trematomus (formerly Pagothenia) bernaccchii and T. newnesi and on tuna Hb indicate the absence of a dominant role for this residue in the Root effect (Ito et al, 1995;Yokoyama et al, 2004;Mazzarella et al, 2006a;Mazzarella et al, 2006b).…”

Section: Vascular Counter-current Exchange In the Rete Mirabilementioning

confidence: 99%

“…In other words, after the first half of subunits has been occupied, low pH appears to essentially block further O 2 binding to the other half of the subunits. At least in tuna (Thunnus thynnus) Hb, the latter are probably the ␤-chains (Yokoyama et al, 2004).…”

Section: Vascular Counter-current Exchange In the Rete Mirabilementioning

confidence: 99%

Historical reconstructions of evolving physiological complexity:O2 secretion in the eye and swimbladder of fishes

Berenbrink

2007

Journal of Experimental Biology

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The traditional realm of comparative physiologists is the phenotype. Researchers in this field are generally interested in how organisms work at the organ system, organ, tissue, cellular, organellar and protein levels of organisation. They are fascinated by the wide range of environmental conditions in which organisms exist and how this is matched by the type and capacity of the physiological mechanisms that they employ. In the post-genomic era, the molecular toolbox of several model species is available in the form of fully sequenced genomes and it can be argued that a true integrative view of how organisms function is incomplete without linking genotypes to the encoded phenotypes in the form of proteins, organelles, cells, etc. A major challenge for experimental biologists in the postgenomic era is therefore trying to close the so-called phenotype-genotype gap.Given the complexity of even a single cell and the emergence of new, unpredictable features at each of the higher levels of biological organisation, it is very difficult, if not impossible, to predict the working of complex physiological systems solely from the underlying genotype. Closure of the phenotype-genotype gap therefore appears a daunting task. Biology, however, unlike physics, can be seen as having already found its single unifying concept, or grand formula: namely evolutionary theory. Thus, looking for the ultimate/evolutionary cause of a physiological mechanism in addition to the proximate/mechanistic cause should help to understand the distribution of particular physiological phenotypes and their associated genotypes in organisms. Thus, the fundamental question for comparative physiologists can be broadened from 'How does it work? ' (Schmidt-Nielsen, 1997a) to 'How did it come about to work like it does? ' (Sherwood et al., 2005a).This review uses the mechanism of oxygen secretion in fishes, which has been intensively studied in the fish swimbladder for over 100·years, to demonstrate the potential insights from such an evolutionary approach. The long generation times of the study species preclude the use of The ability of some fishes to inflate their compressible swimbladder with almost pure oxygen to maintain neutral buoyancy, even against the high hydrostatic pressure several thousand metres below the water surface, has fascinated physiologists for more than 200·years. This review shows how evolutionary reconstruction of the components of such a complex physiological system on a phylogenetic tree can generate new and important insights into the origin of complex phenotypes that are difficult to obtain with a purely mechanistic approach alone. Thus, it is shown that oxygen secretion first evolved in the eyes of fishes, presumably for improved oxygen supply to an avascular, metabolically active retina. Evolution of this system was facilitated by prior changes in the pH dependence of oxygen-binding characteristics of haemoglobin (the Root effect) and in the specific buffer value of haemoglobin. These changes predisposed teleost fishes for the...

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“…The alkaline Bohr effect plays an important role, modifying the oxygen affinity of hemoglobin, increasing its saturation in the lungs or gills and facilitating its release in the tissues, particularly when skeletal muscle tissue releases lactic acid during intense exercise (18).…”

Section: Allosteric Controlmentioning

confidence: 99%

Fish hemoglobins

Souza

Bonilla-Rodriguez

2007

Braz J Med Biol Res

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Vertebrate hemoglobin, contained in erythrocytes, is a globular protein with a quaternary structure composed of 4 globin chains (2 alpha and 2 beta) and a prosthetic group named heme bound to each one. Having myoglobin as an ancestor, hemoglobin acquired the capacity to respond to chemical stimuli that modulate its function according to tissue requirements for oxygen. Fish are generally submitted to spatial and temporal O 2 variations and have developed anatomical, physiological and biochemical strategies to adapt to the changing environmental gas availability. Structurally, most fish hemoglobins are tetrameric; however, those from some species such as lamprey and hagfish dissociate, being monomeric when oxygenated and oligomeric when deoxygenated. Fish blood frequently possesses several hemoglobins; the primary origin of this finding lies in the polymorphism that occurs in the globin loci, an aspect that may occasionally confer advantages to its carriers or even be a harmless evolutionary remnant. On the other hand, the functional properties exhibit different behaviors, ranging from a total absence of responses to allosteric regulation to drastic ones, such as the Root effect.

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1P034 Novel Mechanisms of pH sensitivity in tuna hemoglobin : a structural explanation of the Root effect

Cited by 18 publications

References 0 publications

ATP-induced temperature independence of hemoglobin–O2 affinity in heterothermic billfish

ATP-induced temperature independence of hemoglobin–O2 affinity in heterothermic billfish

Historical reconstructions of evolving physiological complexity:O2 secretion in the eye and swimbladder of fishes

Fish hemoglobins

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