Studies on erythrocruorin III. Oxygen equilibrium of earthworn erythrocruorin

Molecular insights into high-altitude adaption and acclimatisation of Aporrectodea caliginosa

A megabase genome assembly for Aporrectodea caliginosa is presented with transcriptomic and SNP-based evidence for acclimatisation and adaption to extreme weather conditions found at high altitude.

Here, we explore the high-altitude adaptions and acclimatisation of Aporrectodea caliginosa. Population diversity is assessed through mitochondrial barcoding, identifying closely related populations across the island of Pico (Azores). We present the first megabase N50 assembly size (1.2 Mbp) genome for A. caliginosa. High- and low-altitude populations were exposed experimentally to a range of oxygen and temperature conditions, simulating altitudinal conditions, and the transcriptomic responses explored. SNP densities are assessed to identify signatures of selective pressure and their link to differentially expressed genes. The high-altitude A. caliginosa population had lower differential expression and fewer co-expressed genes between conditions, indicating a more condition-refined epigenetic response. Genes identified as under adaptive pressure through F_st and nucleotide diversity in the high-altitude population clustered around the differentially expressed an upstream environmental response control gene, HMGB1. The high-altitude population of A. caliginosa indicated adaption and acclimatisation to high-altitude conditions and suggested resilience to extreme weather events. This mechanistic understanding could help offer a strategy in further identifying other species capable of maintaining soil fertility in extreme environments.

pH dependence of the dissociation of multimeric hemoglobin probed by high hydrostatic pressure

We investigated the thermodynamic features of the classic alkaline dissociation of multimeric hemoglobin (3.1 MDa) from Glossoscolex paulistus (Annelidea) using high hydrostatic pressure. Light scattering measurements up to microscopic thermodynamic equilibrium indicated a high pH dependency of dissociation and association. Electron microscopy and gel filtration corroborated these findings. The volume change of dissociation decreased in absolute values from -48.0 mL/mol of subunit at pH 6.0 to -19.2 mL/mol at pH 9.0, suggesting a lack of protein interactions under alkaline conditions. Concomitantly, an increase in pH reduced the Gibbs free energy of dissociation from 37.7 to 27.5 kJ/mol of subunit. The stoichiometry of proton release calculated from the pressure-induced dissociation curves was +0.602 mol of H(+)/mol of subunit. These results provide a direct quantification of proton participation in stabilizing the aggregated state of the hemoglobin, and contribute to our understanding of protein-protein interactions and of the surrounding conditions that modulate the process of aggregation.

Towards a resolution of the long-standing controversy regarding the molecular mass of extracellular erythrocruorin of the earthworm Lumbricus terrestris

The published molecular mass of erythrocruorin of Lumbricus terrestris and related earthworm species covers a bewildering range of 3.23-4.5 MDa. A critical reexamination reveals that some mass determinations were underestimated and the results do cluster, not at one, but at two values of the molecular mass. One cluster corresponds to approximately 3.6 MDa, as predicted for a stoichiometry of 144 globin and 36 linker chains-the Vinogradov model for the hexagonal bilayer (HBL) assembly of Lumbricus erythrocruorin-and as estimated from the crystal structure of HBL at 5.5 A resolution [Proc. Natl. Acad. Sci. U. S. A. 97 (2000) 7107]. The other cluster corresponds to approximately 4.4 MDa. In addition, a molecular mass of 4.1 MDa, determined by multiangle laser light scattering (MALLS), stands apart of the two clusters, separated from the masses obtained by other methods of molecular mass determination. We propose a stoichiometry of 192 globin and 36 linker chains for the 4.4-MDa molecule. The 36 linkers and 144 out of 192 globin chains are identified with the HBL and the remaining 48 globins are allotted equally to the two halves of the axial cavity above and below the central torus of the structure. The proposed model is supported by the occurrence in some annelid species of erythrocruorin with centrally placed subunits [Biochim. Biophys. Acta 359 (1974) 210], and by the oxidation-dependent shedding of subunits in Lumbricus erythrocruorin. We propose further that the 4.1 MDa determination represents the weight average molecular mass of a population of molecules resulting from a partial dissociation of 4.4-MDa erythrocruorin. This interpretation seems reasonable on the background of the very low protein concentrations ( approximately 100 microg/ml and lower) prevailing at the MALLS experiment.

Nonvertebrate hemoglobins: functions and molecular adaptations

Hemoglobin (Hb) occurs in all the kingdoms of living organisms. Its distribution is episodic among the nonvertebrate groups in contrast to vertebrates. Nonvertebrate Hbs range from single-chain globins found in bacteria, algae, protozoa, and plants to large, multisubunit, multidomain Hbs found in nematodes, molluscs and crustaceans, and the giant annelid and vestimentiferan Hbs comprised of globin and nonglobin subunits. Chimeric hemoglobins have been found recently in bacteria and fungi. Hb occurs intracellularly in specific tissues and in circulating red blood cells (RBCs) and freely dissolved in various body fluids. In addition to transporting and storing O(2) and facilitating its diffusion, several novel Hb functions have emerged, including control of nitric oxide (NO) levels in microorganisms, use of NO to control the level of O(2) in nematodes, binding and transport of sulfide in endosymbiont-harboring species and protection against sulfide, scavenging of O(2 )in symbiotic leguminous plants, O(2 )sensing in bacteria and archaebacteria, and dehaloperoxidase activity useful in detoxification of chlorinated materials. This review focuses on the extensive variation in the functional properties of nonvertebrate Hbs, their O(2 )binding affinities, their homotropic interactions (cooperativity), and the sensitivities of these parameters to temperature and heterotropic effectors such as protons and cations. Whenever possible, it attempts to relate the ligand binding properties to the known molecular structures. The divergent and convergent evolutionary trends evident in the structures and functions of nonvertebrate Hbs appear to be adaptive in extending the inhabitable environment available to Hb-containing organisms.

Oxygen-binding properties of extracellular hemoglobin from the leech, Hirudo medicinalis. Effects of pH, cations and temperature

Electron microscopy of the extracellular hemoglobin from the medicinal leech, Hirudo medicinalis, revealed a typical annelid two-tiered hexagonal structure. The dimensions of the molecule were 30.2 +/- 1.6 nm corner to corner across the hexagon and 18.9 +/- 1.1 nm in height. The oxygenation properties of this high-molecular-weight hemoglobin have been thoroughly studied. The effects of hemoglobin concentration, pH, temperature and concentration of specific cations on the oxygen affinity and the degree of cooperativity have been investigated with special consideration given to physiological conditions. At near-physiological cation concentrations (6 mM Ca2+, 0.125 M Na+), the oxygen affinity and cooperativity tend to increase with increasing alkalinity. At physiological conditions ((pH 7.5) temperature 20 degrees C), they reach P50 values of 5.0 mmHg and n50 = 3.1. An alkaline Bohr effect with considerable magnitude (phi = -0.50) is observed at pH 7.0-8.0. The oxygen-binding properties are also affected by cations. Both oxygen affinity and cooperativity rise with increasing cation concentrations. Divalent cations, such as Ca2+ and Mg2+, bring about larger effects than monovalent ones. They begin to be effective at concentrations as low as 0.1 mM. The magnitude and position of the Bohr effect of H. medicinalis hemoglobin are controlled by cations to such an extent that this Bohr effect can be predominantly ascribable to the oxygen-linked binding of the physiologically available allosteric effectors Ca2+ and Na+. The results obtained indicate that protons and cations are effective allosteric regulators of achaete (leech) extracellular hemoglobins.

Oxygen-binding characteristics of Potamilla chlorocruorin

Accurate oxygen equilibrium curves of chlorocruorin of a marine polychaete annelid, Potamilla leptochaeta, were determined under a variety of experimental conditions. Like chlorocruorins from other species Potamilla chlorocruorin exhibited a low oxygen affinity, a large Bohr effect, and high cooperativity compared to those of human hemoglobin. However, in contrast to chlorocruorins from other species, the shape of the oxygen equilibrium curve for Potamilla chlorocruorin varied dramatically upon changes of pH or temperature. As observed in hemocyanins and annelid hemoglobins, cations, especially divalent ones such as Mg2+ and Ca2+, caused marked increase in oxygen affinity and cooperativity of Potamilla chlorocruorin. This finding together with the determination of cations in Potamilla blood has made clear the physiological role of chlorocruorin as an oxygen carrier. A graphical analysis based on the Monod-Wyman-Changeux allosteric model indicated that the number of sites for oxygen binding involved in heme-heme interactions is six, defining the functional unit of chlorocruorin molecule.

Oxygen binding to Octolasium complanatum erythrocruorin. Modulation of homo- and heterotropic interactions by cations

The functional properties of erythrocruorin from Octolasium complanatum (a common earthworm of Central Italy) have been characterized in great detail. Special attention has been given to the reciprocal effects of the various ligands, namely oxygen, cations and protons. The data obtained under a variety of experimental conditions bring out the dominant role played by cations in the modulation of both homotropic and heterotropic interactions. In this respect, the most interesting observation concerns the unusual interplay between protons and cations that occurs in this erythrocruorin, the first respiratory pigment in which the Bohr effect is due totally to the O2-linked binding of an allosteric effector. The oxygen binding data collected under the various experimental conditions have been analyzed in terms of a modified two-state model, which takes into account the fact that allosteric effectors may also influence the ligand binding properties of the state that they stabilize. The analysis shows that the number of interacting sites necessary for the observed co-operativity in O2 binding is much smaller than the number of heme groups carried by the whole molecule, in accordance with previous findings on hemocyanins, the other class of giant respiratory pigments. Moreover, the analysis indicates that the dimensions of these "functional constellations" are under the control of allosteric effectors.

The dissociation of the extracellular hemoglobin of Tubifex tubifex at extremes of pH and its reassociation upon return to neutrality

The dissociation of the extracellular hemoglobin of Tubifex tubifex at alkaline and acid pH, and its reassociation upon return to neutral pH, was investigated using gel filtration, ultracentrifugation, and polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS-PAGE). Tubifex hemoglobin dissociated at pH above 8 and below 6; both dissociations appeared to be equilibrium processes. The extent of dissociation increased as the pH moved away from neutrality; although dissociation was virtually complete at pH 11, its extent at acid pH did not exceed 50-60% at pH 4. Ca(II), Mg(II), and Sr(II) cations over the range 1-100 mM decreased the extent of the dissociation only at alkaline pH. The visible absorption spectrum of the oxyhemoglobin remained unaltered in the pH range 4-9. At more extreme pH, it changed with time, altering irreversibly to that of the aquo ferri form. Gel filtration of the hemoglobin at both extremes of pH showed that it dissociated into two heme-containing fragments; one consisting of subunit 1 (Mr approximately 17,000) and the other containing subunits 2, 3, and 4 of the hemoglobin (Mr approximately 60,000). Upon return to neutral pH, the dissociated fragment reassociated to the extent of 50 to 80% to whole hemoglobin molecules. The reassociation decreased with increase in alkaline pH, and with decrease in acid pH to which the hemoglobin had been exposed; it increased in the presence of Ca(II), Sr(II), and Mg(II) only subsequent to dissociation at alkaline pH. The SDS-PAGE patterns, gel-filtration elution volumes, and alpha-helical contents, determined from circular dichroism at 222 nm, of the reassociated whole molecules were identical to those of the native hemoglobin.

Dissociation and oxygen equilibrium properties of the extracellular hemoglobin of Eisenia foetida

The dissociation and oxygen equilibrium properties of whole blood and the purified hemoglobin from Eisenia foetida were compared. Oxygen affinities agreed approximately with each other in the range of pH 6.0 to 9.5. The values of n1/2 were higher in whole blood than in the purified hemoglobin between pH 7.0 and 9.5. The maximum values, obtained near pH 8, were about 6 in whole blood and 3.5 in the purified hemoglobin. In the purified hemoglobin, alkaline dissociation started at pH 7.8, and the approximately 60 S whole molecule dissociated completely into approximately 10 S and 5-6 S components at pH 9.1. In whole blood, however, the dissociation started at pH 8.2 and the complete disappearance of the approximately 60 S molecule occurred at pH 9.6. The values of n1/2 for the dissociation products were lower than those of the purified hemoglobin between pH 7.0 and 9.0. The value of n1/2 decreased with increasing dissociation of the approximately 60 S whole molecule with a pH rise in both whole blood and the purified hemoglobin. Addition of CaCl2 or MgCl2 up to 10 mM to the purified hemoglobin at pH 8.0-8.1 induced increases in oxygen affinity and cooperativity and in the stability of the approximately 60 S whole molecule. The effect on the oxygenation properties was greater with CaCl2 than MgCl2 at the same molar concentration. The stabilizing effect on the approximately 60 S molecule was almost the same with both CaCl2 and MgCl2. These results suggest that the dissociation of property of the hemoglobin in whole blood is controlled by both Ca2+ and Mg2+, and that its oxygenation property is controlled by Ca2+.

Dissociation and oxygen equilibrium properties of earthworm (Pheretima hilgendorfi) hemoglobin

The dissociation and oxygen equilibrium properties of the purified hemoglobin and whole blood obtained from the earthworm Pheretima hilgendorfi were compared. Above pH 8.0, P1/2's were higher in the purified hemoglobin than in whole blood, while below pH 8.0, nearly identical P1/2's were observed in both materials and P1/2 was at a maximum at pH 6.5. The values of n1/2 were higher in whole blood than in the purified hemoglobin at alkaline pH. The maximum values of n1/2 were observed around pH 8.1 in the purified hemoglobin and pH 8.7 in whole blood, and the values were 5.3 and 9.5, respectively. In the purified hemoglobin, a small amount of dissociation component was already observed at pH 8.0, while in whole blood, no dissociation occurred up to pH 9.1. Dialysis of whole blood or addition of 10 mM EDTA to whole blood at alkaline pH induced the loss of the enhanced cooperativity, the increased oxygen affinity and the high stability of the 60 S whole molecule. These results strongly suggest that divalent cations are participating in the functional and dissociation properties of the whole blood of this species.

The erythrocruorin of Eisenia fetida. I. Properties and subunit structure

The erythrocruorin of Eisenia fetida possesses a relative molecular mass, determined by sedimentation equilibrium, of (3.82 +/- 0.05) . 10(6). According to the iron and heme contents, 0.218 +/- 0.008% and 2.34 +/- 0.02% by mass, respectively, it contains 144 hemes per molecule. The dimensions of the molecule observed by electron microscopy are 25.0 X 16.5 nm (diameter X height). SDS-polyacrylamide gel electrophoresis indicates that the erythrocruorin consists of six subunits (Mr 14,900, 15,300, 17,200, 19,700, 31,600 and 40,000). Oxygen binding studies showed that E. fetida erythrocruorin has a high oxygen affinity (P50 = 2.8 Torr at pH 7.5), exhibits a slight bohr effect and possesses a high cooperativity with the Hill coefficient h = 3.7-4.8. Treatment of the erythrocruorin either by freezing and thawing or by aging or exposure to alkaline pH converts it irreversibly into a state of lower cooperativity with h = 2.0-2.6. A model of the subunit structure of the erythrocruorin is proposed which takes into account the physiochemical and oxygen-binding properties of the erythrocruorin and the subunits obtained upon its dissociation.

The erythrocruorin of Eisenia fetida. II. Properties of the principal subunit

The erythrocruorin of Eisenia fetida can be dissociated partially into its principal subunits, the putative one-twelfths of the molecule and smaller subunits, by three different methods: freezing and thawing (Af), exposure to alkaline pH (Aa) and aging (Ao). The isolated subunits possess a relative molecular mass of 310,000 +/- 20,000 by gel filtration and their SDS-polyacrylamide gel electrophoretic patterns are identical to (Af) or slightly different from (Aa, Ao) that of the erythrocruorin. The absorption spectra and Hill constant h of the principal subunit Af correspond to the values of the whole erythrocruorin in the state of low cooperativity, which results from freezing and thawing, exposure to alkaline pH, and aging. Electron microscopic studies of the principal subunits and of the 'treated' erythrocruorin showed that their dimensions had increased relative to the native erythrocruorin: a diameter of 9 nm vs. 8.5 nm and (26.4 +/- 0.4) X (18.3 +/- 0.4) nm vs. 25.0 X 16.5 nm, respectively. Erythrocruorin reconstituted from the Af subunits possessed the dimensions (26.6 +/- 0.4) X (18.6 +/- 0.4) nm. Based on the subunit model of Eisenia erythrocruorin proposed previously it is suggested that there can exist an association-dissociation equilibrium between the principal subunits, smaller subunits, and the erythrocruorin when it is in the state of low cooperativity, but not when it is in its native, high-cooperativity state.

The physico-chemical and functional properties of Abarenicola affinis affinis (Ashworth) extracellular haemoglobin (erythrocruorin)

The purified erythrocruorin from the Arenicolid polychaete, Abarenicola affinis affinis (Ashworth) has an S020,w of 57.5 S, and a molecular weight of 3.29 . 10(6) as determined by sedimentation equilibrium at pH 7.0. In the electron microscope it displays a two-tiered hexagonal array characteristic of other annelid erythrocruorins and chlorocruorins, with dimensions of approximately 25.5 nm diameter and 17.0 nm height. The isoelectric point of the molecule is at pH 4.63, and its amino acid composition and absorption spectrum are similar to those of other annelid erythrocruorins. The haem and iron contents are 2.77% and 0.23%, corresponding to minimum molecular weights of 22 250 and 24 800, respectively. In pH-induced dissociation studies, the erythrocruorin is found to be stabilized by Ca2+ up to pH 8.6, while in the presence of EDTA, dissociation begins at pH 7.8. In discontinuous gel electrophoresis, dissociated erythrocruorin gives subunits with molecular weights 263 000, 117 500, 68 400, 35 900 and 28 800, while, in detergent electrophoresis in the presence of 2-mercaptoethanol, polypeptide chains with molecular weights 13 700, 15 800, 24 700, 27 800 and 33 600 are obtained. Abarenicola erythrocruorin is also shown to bind oxygen cooperatively with a Hill coefficient h = 4.0 and P50 = 6.0 mmHg at pH 7.0 and 25 degrees C. Over the pH range of 7.0 to 7.8 the molecule lacks an alkaline Bohr effect.

The subunits of Abarenicola affinis affinis (Ashworth) extracellular haemoglobin (erythrocruorin)

The subunits of the erythrocruorin of Abarenicola affinis affinis (Ashworth) were investigated by various physicochemical methods. Gel chromatography at pH 9.0 in Sephadex G-200 gave three main protein peaks with molecular weights of 240 000, 100 000 and 31 000, respectively. Polyacrylamide gel electrophoresis showed considerable heterogeneity in the subunits, although the main components gave similar molecular weight ranges to the above. Anomalous results were also obtained in SDS-polyacrylamide gel electrophoresis. In the analytical ultracentrifuge, the subunit from the first peak showed a sedimentation coefficient of 10 S and Mw 250 000, and the second yielded s20,w = 5 S. Functionally, the 10 S subunit showed cooperative oxygen binding, but the Hill coefficient was lower than that observed for the native molecule. A possible model for the subunit structure of Abarenicola affinis affinis erythrocruorin is discussed.

Amphitrite ornata erythrocruorin. II. Molecular controls of function

In the marine terebellid worm Amphitrite ornata the vascular fluid contains a high molecular weight erythrocruorin, while cells of the coelom contain a monomeric hemoglobin. The structural integrity of the erythrocruorin molecule is known to be dependent on the presence of a minimal concentration of divalent cations (1-3 mM) in the medium. The functional properties of Amphitrite erythrocruorin are also affected by cations. The oxygen affinity tends to increase with increasing cation concentration and the degree of cooperative interactions, expressed in the kinetics and equilibria of ligand binding, goes through a maximum. Maximal Hill coefficients of 3-4 are observed with 50 mM CaCl2, 50 mM MgCl2 or 1 M NaCl in measurements at the physiological pH of 7.75. Only 2 mM CaCl2 is required for maximal cooperativity at pH 8.5. This suggests partial deprotonation of the cation binding site at high pH. It is somewhat unusual that pH effects on cooperativity are reversible, since this is not a common feature of the giant erythrocruorin molecules. The oxygen binding experiments revealed a marked effect of divalent cations of Amphitrite erythrocruorin at high pH and cation concentration. Above pH 8.5, at 50 mM CaCl2 and 12 degrees C, the erythrocruorin will form a polymer upon deoxygenation. This polymerization is readily reversible by bringing the temperature for 12 to 20 degrees C or by oxygenation. Under physiological conditions of pH and cation concentration and at 12 degrees C, the erythrocruorin and the monomeric coelomic hemoglobin require a similar oxygen pressure for half saturation. However, the allosteric regulation of function is absent for the coelomic protein.

Studies on erythrocruorin. VII. Reconstitution of earthworm erythrocruorin from the apoprotein

Apoerythrocruorin prepared from the giant respiratory hemoprotein of the earthworm (60 S, Mr = 3 X 10(-6)) is an electrophoretically homogeneous molecule which sediments as a single peak of low molecular weight (3.5 S) and has a lower alpha-helical content (approx. 30%) than the native protein. Titration of globin with ferric heme indicates the presence of different binding sites; however, after purification by ion exchange chromatography, the reconstitution product contains 1 haem/23 000 g of protein as the native molecule. Reconstituted ferric erythrocruorin is a low molecular weight hemichrome with the same optical and physicochemical properties of the hemichrome formed by natural ferric erythrocruorin. Reconstituted ferrous erythrocruorin reacquires the alpha-helical content and the quaternary structure of the native molecule. Reassociation into 10-S speices (1/12 of the whole molecules) is fast and easy, while that into whole molecules is slow and somewhat erratic. The functional properties of reconstituted ferrous erythrocruorin (oxygen affinity, cooperativity in oxygen binding, magnitude of Bohr effect) are very similar to those of the "stable" low cooperativity form of the undissociated protein.

Characterization of the extracellular haemoglobin of Haemopsis sanguisuga (L.)

The haemoglobin from the blood of the horseleech, Haemopsis sanguisuga (L.), had a sedimentation coefficient, SO20, w, of 59.11 +/- 0.55 S, and a molecular weight as determined by sedimentation equilibrium of 3.71 X 10(6)+/-9904 X 10(6). In the electron microscope the molecule appeared to be made up of two hexagonal plates, as is found with other worm haemoglobins, with dimensions 24.4+/-2.0 nm (across the hexagon) and 15.2+/-1.4 nm (height). The amino acid composition and spectrum were closely similar to those of the haemoglobins of other annelids (e.g. Lumbricus). The alpha-helical content, calculated from circular-dichroism measurements in the far-u.v. region, was 56-63%. The haem content was 2.49%, corresponding to a minimum molecular weight per haem group of 24 800, but detergent-gel electrophoresis indicated the presence of polypeptide chains of mol.wts. 12 600, 14 800, 15 500 and 25 100. The pH-induced dissociation of the native molecule yielded compotosol of Soya-bean root nodules.

Kinetics of binding of carbon monoxide to lumbricus erythrocruorin: a possible model

This paper represents a kinetic study of the binding of carbon monoxide by Lumbricus erythrocruorin. Observations on the quantum and the relaxation of the system both to equilibrium and to the steady state realized in the presence of constant illumination under various conditions are reported. The results, besides indicating the existence of at least two types of binding sites, give indications as to the behavior of a complex polyfunctional molecule, such as an enzyme, working under steady-state conditions.