Structure/Function Relationships in the Hemoglobin Components from Moray (Muraena Helena)

Abstract

Concerning thc number and type of the hemoglobin componcnts, the morny M u r u~i t i~ heleiia is characterized by three diffcrcnt phenotypes whose frequencies arc ncarly identical. Thus, the cathodal cornponent is present in all individuals, whereas one or both of two anodal components may be present in the same phenotype. These components have been separated by chromatography.The oxygen binding properties of the purified hcmoglobin components have been studied in the ahse,nce and presence of saturating concentrations of ATP or GTP and as a function of pH. The cathodal component shows an intrinsic 0, affinity four times higher than that of both aiiodal components, : I very sinall Bohr effect and a significant decrease in affinity upon addition of ATP and GTP (three and four times respectively with respect to stripped conditions), the latter being more cffcctivc than the former over the entire pH range exainincd. The anodal components do not appear functionally distinguishable and show the presence of iiii enhanced Bohr effect (Root effect) that is under the strict control of niicleotide triphosphates ATP, GTP, which, unlike in the cathodic component, cxert the same effect on oxygen affinity. The complete sequence of the chains of the cathodal iind of one of the anodal components have been determined.The possible molecular basis of these different functional characteristics are discussed in thc light of the globiii scquence and of thosc amino acid residues which are known to be responsiblc of hemoglobin functional behaviour.Krywords: hemoglobin ; oxygen binding; heterotropic interactions; uniino acid sequence ; moray.Comparative studies on Hb function havc ii special interest since they may lead to an understanding of those changes which, in the course of cvolution, have rtevcloped in different organisms to meet specific physiological requirements. In fact, besides contrihuting to a verification of the generality of the molecular mechanisms proposed for mammalian Hbs, a coniparativc approach may yield inforination on the kcatures involved in the evolutionury processes. In this respect, Hbs exhibit a great dcal of variation in terms of absolute affinities for oxygen and in their susceptibility to metabolic effectors such as 2,3-bisphosphoglycerale, ATP and GTP. This type ol' fine tuning is devcloped to i l high degree in all vertebratc Hbs and is primarily based on the ability of the cffector to preferentially bind one of the lwo qiiaternary conformations ('I and R slates in the simplrst modcl).Along thesc lines, specks having inultiple Hbs in their blood are of intercst i n so fiir as multiplicity of components is an evolutioxary response to the special needs of the individual. In fact, structural multiplicity is very often accompanied by i l niore or less marked fiinclional heterogeneity that has to be linked to sonic specific physiological rcquirements of the species. Hence, studies on Hb multiplicity may provide valuable information on structurc/fiinction relationships in gas-binding proteins and on ('cim.~l,o...

Evolution of globin genes of the medaka Oryzias latipes (Euteleostei; Beloniformes; Oryziinae)

“…3 and 4). Both the moray Muraena helena (Pellegrini et al, 1995) and the bimodal gill(water)/gut(air)-breathing Amazon catfish Hoplosternum littorale (Weber et al, 2000) have cathodic and anodic hemoglobin components also. Their a and b globins belong to two different clades, the Cathodic and Anodic Adult Hb Groups.…”

Hemoglobin function in deep-sea and hydrothermal-vent endemic fish:Symenchelis parasitica(Anguillidae) andThermarces cerberus(Zoarcidae)

“…Whereas 'class I' species, such as cyprinids and ciclids (Gillen and Riggs, 1972), possess only electrophoretically anodic Hb components with relatively low O2 affinities and pronounced Bohr and Root effects (decreases in O2 affinity and carrying capacity, respectively, at low pH that promote O2 unloading in the respiring tissues and in the swimbladder), 'class II' fish (including eels, salmonids and some catfish) additionally have cathodic Hbs that exhibit high intrinsic O2 affinities and low pH sensitivities (Powers and Edmundson, 1972;Gillen and Riggs, 1973;Weber et al, 1976aWeber et al, , 2000Pellegrini et al, 1995) and may function as a reserve transport system when oxygenation of the anodic components is compromised by acidification and hypoxia (Weber, 1990(Weber, , 2000a.…”

The Bohr effect of haemoglobin in vertebrates: an example of molecular adaptation to different physiological requirements

“…The Hb system of Anguilliformes such as eel (Pellegrini et al. 2003) and moray (Pellegrini et al. 1995) is similar to the extensively studied trout system (Brunori et al.…”

“…0.1 m Bis‐Tris or Tris buffer plus 0.1 m NaCl, in the absence (○, •) and presence of 1 m m ATP (▵, ▴) or GTP (□, ▪). Modified from Pellegrini et al. (1995).…”