Isohemoglobin differentiation in the bimodal-breathing amazon catfish Hoplosternum littorale

The bimodal gill(water)/gut(air)-breathing Amazonian catfish Hoplosternum littorale that frequents hypoxic habitats uses "mammalian" 2,3-diphosphoglycerate (DPG) in addition to "piscine" ATP and GTP as erythrocytic O(2) affinity modulators. Its electrophoretically distinct anodic and cathodic hemoglobins (Hb(An) and Hb(Ca)) were isolated for functional and molecular characterization. In contrast to Hb(An), phosphate-free Hb(Ca) exhibits a pronounced reverse Bohr effect (increased O(2) affinity with decreasing pH) that is obliterated by ATP, and opposite pH dependences of K(T) (O(2) association constant of low affinity, tense state) and the overall heat of oxygenation. Dose-response curves indicate small chloride effects and pronounced and differentiated phosphate effects, DPG < ATP < GTP < IHP. Hb(Ca)-O(2) equilibria analyzed in terms of the Monod-Wyman-Changeux model show that small T state bond energy differences underlie the differentiated phosphate effects. Synthetic peptides, corresponding to N-terminal fragment of the cytoplasmic domain of trout band 3 protein, undergo oxygenation-linked binding to Hb(Ca), suggesting a metabolic regulatory role for this hemoglobin. The amino acid sequences for the alpha and beta chains of Hb(Ca) obtained by Edman degradation and cDNA sequencing show unusual substitutions at the phosphate-binding site that are discussed in terms of its reverse Bohr effect and anion sensitivities.

Gas transfer system in Alvinella pompejana (Annelida polychaeta, Terebellida): functional properties of intracellular and extracellular hemoglobins

Alvinella pompejana is a tubicolous polychaete that dwells in the hottest part of the hydrothermal vent ecosystem in a highly variable mixture of vent (350 degrees C, anoxic, CO(2)- and sulfide-rich) and deep-sea (2 degrees C, mildly hypoxic) waters. This species has developed distinct-and specifically respiratory-adaptations to this challenging environment. An internal gas exchange system has recently been described, along with the report of an intracellular coelomic hemoglobin, in addition to the previously known extracellular vascular hemoglobin. This article reports the structure of coelomic hemoglobin and the functional properties of both hemoglobins in order to assess possible oxygen transfer. Coelomocytes contain a unique monomeric hemoglobin with a molecular weight of 14,810+/-1.5 Da, as determined by mass spectrometry. The functional properties of both hemoglobins are unexpectedly very similar under the same conditions of pH (6.1-8.2) and temperature (10 degrees -40 degrees C). The oxygen affinity of both proteins is relatively high (P50=0.66 Torr at 20 degrees C and pH 7), which facilitates oxygen uptake from the hypoxic environment. A strong Bohr effect (Phi ranging from -0.8 to -1.0) allows the release of oxygen to acidic tissues. Such similar properties imply a possible bidirectional transfer of oxygen between the two hemoglobins in the perioesophagal pouch, a mechanism that could moderate environmental variations of oxygen concentration and maintain brain oxygenation.

The role of amino acid alpha38 in the control of oxygen binding to human adult and embryonic haemoglobin Portland

The role of the amino acid at position alpha(38) in haemoglobin has been probed using site-directed mutagenesis. When the Thr residue at position alpha(38) (which is totally conserved in all mammals) is changed to a Gln, the equilibrium properties of the protein are significantly altered. Equilibrium and kinetic data show that the R-state properties of the protein are essentially unaffected by the mutation whilst the allosteric equilibrium and T-state properties are changed. Mutation of the naturally occurring Gln(38) of the human embryonic haemoglobin zeta-chain (the only known non-Thr containing globin) to a Thr residue shows the converse change in properties produced by the adult mutation, although in this case the situation is complicated by significant chain heterogeneity in the T state. An extension of the two-state model of co-operativity is presented to describe quantitatively the equilibrium ligand binding in the presence of T-state chain heterogeneity. A molecular model is described in which the putative interaction of alphaGln(38) and betaTyr(145) is identified which make a significant contribution to the previously reported unusual ligand-binding properties of the zeta-chain containing human embryonic haemoglobins.

The role of linkers in the reassembly of the 3.6 MDa hexagonal bilayer hemoglobin from Lumbricus terrestris

The extent and kinetics of reassembly of the four groups of linkers L1-L4 with 213 kDa subassemblies of twelve globin chains D, (bac)3(d)3, isolated from the approximately 3.6 MDa hexagonal bilayer (HBL) hemoglobin (Hb) of Lumbricus terrestris, was investigated using gel filtration. The reassembled HBL's were characterized by scanning transmission electron microscopic (STEM) mass mapping and their subunit content determined by reversed-phase chromatography. In reassembly by method (A), the linkers isolated by RP-HPLC at pH approximately 2.2 were added to D at neutral pH; in method (B), the linkers were renatured at neutral pH and then added to D. With method (A) the percentage of HBL reassembly varied from >/=13% in the absence of Ca(II) to </=75% in 1-10 mM Ca(II). Reassembly to HBL structures whose linker contents, STEM images and masses were similar to the native Hb was observed with all the linkers (>/=75%), with ternary and binary linker combinations (40-50%) and with individual linkers producing yields increasing in the following order: L1=1-3%, L2 approximately L3=10-20% and L4=35-55%. The yield was two- to eightfold lower with method (B), except in the case of linkers L1-L3. Although the reassembly kinetics were always biphasic, with t1/2=0.3-3.3 hours and 10-480 hours, the ratio of the amplitudes fast:slow was 1:0.6 with method (A) and 1:2.5 with method (B). These results are consistent with a scheme in which the slow HBL reassembly is dependent on a slow conversion of linker conformation at neutral pH from a reassembly incompetent to a reassembly competent conformation. Although all the linkers self-associate extensively at neutral pH, forming complexes ranging from dimers to >18-mers, the size of the complex does not affect the extent or rate of reassembly. The oxygen binding affinity of reassembled HBLs was similar to that of the native Hb, but their cooperativity was lower. A model of HBL reassembly was proposed which postulates that binding of linker dimers to two of the three T subunits of D causes conformational alterations resulting in the formation of complementary binding sites which permit lateral self-association of D subassemblies, and thus dictate the formation of a hexagonal structure due to the 3-fold symmetry of D.

Functional differentiation in trematode hemoglobin isoforms

The Hbs and the major electrophoretic Hb components (isoHbs) were isolated from three species of the trematodes, Explanatum explanatum (Ee), Gastrothylax crumenifer (Gc) and Paramphistomum epiclitum (Pe), that parasitise the common Indian water buffalo Bubalus bubalis. The Hbs are monomeric and resemble the so-called nonfunctional mutant hemoglobins that have Tyr at B10 or E7 positions (replacing Leu and the His residues, respectively). However, they are capable of binding with O2 and CO. O2 equilibrium studies of trematode Hb isoforms reveal extremely high O2 affinities, with half-saturation O2 tension (P50) values up to 800 times lower than those of human hemoglobins. This correlates with Tyr residues at B10 and at the distal position (E7) that decrease the O2 dissociation rate by contributing hydrogen bonds (H-bonds) to the bound O2. These substitutions also increase the O2 association rates either due to orientation of E7-Tyr towards the solvent and/or by sterically hindering the entry of water molecules into the heme pocket. The latter may account for the low rate of autoxidation of trematode Hbs. The Hbs and their isoforms from different species exhibited pronounced variation in O2 affinity, which may relate to subtle differences in the structure of the heme pocket. The O2 affinities of the composite (unfractionated) Hbs were intermediate to those of the individual Hb isoform. The P50 values of Hbs here obtained by direct O2 equilibrium measurements differed from those calculated from kinetic data already published [Kiger, L., Rashid, A. K., Griffon, N., Haque, M., Moens, L.,Gibson, Q. H., Poyart, C., & Marden, M. C. (1998). Biophys. J. 75, 990-998.] Intermediate state(s) due to slow reorientation of E7-Tyr may account for this difference. Some Hb isoforms showed slight (either normal or reverse) Bohr effects. The hyperbolic O2 equilibrium curve, Hill coefficient (n) values near unity accord with a monomeric nature of trematode Hbs. In marked contrast to vertebrate Hbs, CO does not seem to compete effectively with O2 in trematode Hbs, as evident from partition coefficient values (M) below 1.

Characterization and functional properties of the extracellular coelomic hemoglobins from the deep-sea, hydrothermal vent scaleworm Branchipolynoe symmytilida

Polychaete species belonging to the genus Branchipolynoe are commensal with mussels from deep-sea hydrothermal vents and cold-seeps. Possessing hemoglobins (Hbs), the species B. symmytilida, which is found in the mussel Bathymodiolus thermophilus on the East Pacific Rise, is exceptional in a family normally devoid of respiratory pigments. In a previous paper we described two major coelomic extracellular hemoglobins with unique quaternary structures. Aiming to discern respiratory adaptations to the highly variable hydrothermal environment, this paper characterizes the functional properties of these Hbs and the coelomic fluid. The two major hemoglobins (C1 and C2) exhibit spectrophotometric characteristics of both intra- and extracellular hemoglobins. However, their amino acid content is very different from other known hemoglobins and is characterized by a high proportion of alanine and glycine (up to 40% cumulated in C1). C1 and C2 differ markedly by their cysteine content (0.8% and 13% respectively). The coelomic fluid exhibits a strong buffer capacity due to the high hemoglobin content (3 mM heme). In vitro, CO2 accumulation (up to 10-12 mM CO2 for PCO2 = 7.5 Torr) occurs with limited pH changes and is only partly accounted for by carbamino-Hb formation. The two hemoglobins exhibit high oxygen-affinities (P50 0.4 Torr for C1 and 0.9 Torr for C2, at 10 degrees C, pH 8) and a normal Bohr effect (phi values ranging from -0.54 and -0.37 at 10 degrees C, to -0.24 and -0.28 at 30 degrees C, for C1 and C2, respectively). Cooperativity values range from 0.8 to 1.9 for C1 and from 0.8 to 1.7 for C2. The temperature sensitivity of O2 affinity reflect deltaH values that decrease from -30 to -60 kJ x mol(-1) with increasing pH. C2 exhibits a slight specific effect of CO2 on oxygenation properties.

Oxygen binding and its allosteric control in hemoglobin of the pulmonate snail, Biomphalaria glabrata

Pulmonate snails that experience extreme variations in gas tensions and temperatures possess extracellular, high-molecular mass ( approximately 1.7 x 10(6) Da) hemoglobins (Hbs) that are little known as regards oxygenation and allosteric characteristics. Biomphalaria glabrata hemolymph exhibits a high O2 affinity (half-saturation O2 tension = 6.1 mmHg; pH 7.7, 25 degreesC), pronounced Bohr effect (Bohr factor = -0.5), and pH-dependent cooperativity (Hill's cooperativity coefficient at half-saturation = 1.1-2.0). Divalent cations increase O2 affinity, Ca2+ exerting greater effect than Mg2+. Analyses in terms of the Monod-Wyman-Changeux model indicate novel O2 affinity control mechanisms. In contrast to vertebrate Hb, where organic phosphates and protons lower affinity via decreased O2 association equilibrium constant of Hb in low-affinity state (KT), and to extracellular annelid Hbs, where protons and cations primarily modulate O2 association equilibrium constant of Hb in high-affinity state (KR), in B. glabrata Hb, the Bohr effect is mediated predominantly via KR and the cation effect via KT, reflecting preferential, oxygenation-linked proton binding to oxygenated Hb and cation binding to deoxygenated Hb. CO2 has no specific (pH independent) effect. Nonlinear van't Hoff plots show temperature dependence of the overall heats of oxygenation, indicating oxy-deoxy heat capacity differences. The findings are related to possible physiological significance in pond habitats.

Interaction between haemoglobin and synthetic peptides of the N-terminal cytoplasmic fragment of trout band 3 (AE1) protein

Two acidic peptides corresponding to the first 10 and 20 amino acid residues of the N-terminal, cytoplasmic fragment of rainbow trout band 3 (AE1) protein were synthesised in order to study their interaction with trout and human haemoglobin (Hb). The peptides did not influence the oxygen affinity of the main anodic trout Hb component (Hb IV) when tested at surplus peptide concentration ([peptide]/[Hb4]=16), at high and low ionic strength and at pH values ranging from 6.5 to 7.6. With human Hb, however, the 20-mer peptide markedly decreased the oxygen affinity and increased the Bohr effect. These data suggest that the trout band 3 peptide binds preferentially to the deoxy (T) conformation of human Hb, probably at the organic phosphate binding site in the central cavity between the beta-chains, which is known to be the binding site for the acidic N terminus of human band 3. In trout Hb IV, the presence of negatively charged Asp at position NA2 of the beta-chains (in contrast to positive or neutral residues in mammalian Hb) may weaken any interaction with the highly negatively charged peptides.

Hydrogen ion titrations of the anodic and cathodic haemoglobin components of the European eel Anguilla anguilla

H+ titrations were conducted on the separated haemoglobin components of eel Anguilla anguilla in both the oxygenated and deoxygenated states. In anodic haemoglobin, the addition of GTP, and to a lesser extent C1-, increased the magnitude of the Haldane effect and shifted its maximum value into the in vivo pH range. Of the 22 histidine residues in the anodic component, only approximately seven were titratable, presumably the beta-chain residues at positions 41, 97, 109 and 146 (helical positions C7, FG4, G11 and HC3, respectively). In cathodic haemoglobin, a small negative Haldane effect was observed at pH values between 6.8 and 8.5 which disappeared in the presence of GTP (molar ratio 3:1 GTP:haemoglobin tetramer). GTP had virtually no effect on the buffer value at fixed oxygenation status, and the lowest buffer value was observed at in vivo pH values. No titratable histidine residues were observed in the cathodic component, indicating that all 14 histidines in this component are buried. We conclude that the anodic component, which constitutes two-thirds of the haemoglobin in the eel, plays the predominant role in CO2 transport and pH homeostasis in vivo.

Characterization of the myoglobin and its coding gene of the mollusc Biomphalaria glabrata

A cDNA clone isolated from a Biomphalaria glabrata (Mollusca, Gastropoda) neural cDNA library was identified as encoding a myoglobin-like protein of 148 amino acids with a single domain and a calculated mass of 16,049.29. Alignment with globin sequences with known tertiary structure confirms its overall globin nature. The expressed myoglobin was identified in the radular muscle and isolated. Oxygen equilibrium measurements on the protein reveal a high oxygen affinity. Val-B10 and Gln-E7, important residues for the determination of the oxygen affinity, are strikingly different from the standard molluscan pattern (Conti, E., Moser, C., Rizzi, M., Mattevi, A., Lionetti, C., Coda, A., Ascenzi, P., Brunori, M., Bolognesi, M. (1993) J. Mol. Biol. 233, 498-508). The single gene encoding the globin chain is interrupted by three introns at positions A3.2, B12.2, and G7.0. Comparison with other nonvertebrate globin genes reveals on the one hand conservation (B12.2 and G7.0) and on the other hand variability of the insertion positions (A3.2). The Biomphalaria myoglobin sequence was used together with all other molluscan globin sequences available to assess the origin and phylogeny of the phylum. Our results confirm the doubts raised about monophyletic origin of the Mollusca, which was first observed using SSU rRNA as a molecular marker.

Primary structures of Arenicola marina isomyoglobins: molecular basis for functional heterogeneity

The primary structures of isomyoglobins MbI and MbII from the body wall musculature of the polychaete Arenicola marina were investigated, aiming to trace the molecular basis for their functional differentiation. Unexpectedly, five chains, MbIa, MbIb, MbIIa, MbIIb and MbIIc, each consisting of 145 amino-acid residues and occurring in a ratio of = 33:17:25:12.5:12.5 were found. All substitutions can be explained by one-point mutations. With the exception of the 41(C6)Asn-->Asp(MbI/MbII) exchange that appears to be the basis for the electrophoretic separation of MbI and MbII, the substitutions do not involve drastic changes in the character of the side-chains. Pairwise comparison of MbIa and MbIIa with other invertebrate globin chains indicate the following sequence of decreasing identities: Aplysia (mollusc) Mb, Chironomus (insect) CTT III hemoglobin, whale Mb and Ascaris (nematode) Mb. The marked difference in O2 affinities between MbI and MbII appears attributable to 62Pro which distorts the E helix around E6 and occurs in all MbII chains, but in only 33% of the MbI chains (MbIb).

A two-state analysis of co-operative oxygen binding in the three human embryonic haemoglobins

The binding of oxygen to the three human embryonic haemoglobins, at pH 7.4, has been shown to occur as a co-operative process. Analysis of oxygen-binding curves obtained in the absence of organic phosphate allosteric effectors shows that the process can be described quite accurately by the two-state model of allosteric action. In the presence of organic phosphates, the binding affinity for oxygen to the T-state of the alpha 2 epsilon 2 and zeta 2 epsilon 2 haemoglobins is significantly lowered. The values of the best-fit two-state parameters determined for each of the embryonic haemoglobins together with the temperature-dependence of the overall equilibrium binding process are discussed in terms of oxygen transfer from the maternal blood supply. Fast-reaction studies have been used to determine the rate constants of the oxygen association and dissociation processes occurring in the R-state and the rate of the allosteric R > T conformational transition. Analysis of these data suggests a likely reason for the high affinity and low co-operativity of the embryonic proteins and identifies the origins of the inability of equilibrium measurements to identify chain non-equivalence in the R-state.

The anodic hemoglobin of Anguilla anguilla. Molecular basis for allosteric effects in a root-effect hemoglobin

The functional and structural basis for the Root effect has been investigated in the anodic hemoglobin of the European eel, Anguilla anguilla. This hemoglobin exhibits a large Bohr effect, which is accounted for by oxygen-linked binding of seven to eight protons in the presence of GTP at pH 7.5. Oxygen equilibrium curves show nonlinear lower asymptote of Hill plots, indicating the occurrence of heme-heme interactions within the T state. Analysis of the curves according to the co-operon model (Brunori, M., Coletta, M., and Di Cera, E. (1986) Biophys. Chem. 23, 215-222) reveals that T state cooperativity is positive at high pH and in the stripped hemoglobin (where the T --> R allosteric transition is operative) and negative at low pH and in the presence of organic phosphate (where the molecule is locked in the low affinity structure), indicating site heterogeneity. The complete amino acid sequence of eel anodic hemoglobin has been established and compared with that of other fish hemoglobins. The presence of the Root effect correlates with a specific configuration of the alpha1beta2 switch interface, which at low pH would stabilize subunit ligation in the T state without changing the quaternary structure. We propose that the major groups involved in the binding of oxygen-linked protons in eel anodic hemoglobin are located on the beta chain and comprise His-HC3 at the C terminus, His-FG4 at the switch interface, and Lys-EF6 and the N terminus at the phosphate-binding site.

Oxygen binding and aggregation of hemoglobin from the common European frog, Rana temporaria

The hemoglobin from the European frog, Rana temporaria, consists of one major and three minor components. The tetramers aggregate upon deoxygenation notably at pH 7:3. Aggregation due to formation of disulphide bridges, as occurs in related species, was observed only in polyacrylamide gels. The hemolysate showed a pronounced Bohr effect. Oxygen affinity decreased with increasing hemoglobin concentration, indicating that aggregation affects the functional properties of the hemolysate. Oxygen binding equilibria of unfractionated hemolysate are insensitive to chloride and show low sensitivity to ATP. Analysis of oxygen equilibrium curves in terms of the two-state allosteric model (MWC) showed that pH change exerted a greater effect on the association constant of the oxygenated state (KR) than that of the deoxy state (KT). The number of interacting binding sites (q) increased with hemoglobin concentration. Cooperativity of oxygen binding, evaluated as Hill coefficient n, never exceeded the value of 3.0. Earlier studies on hemoglobin and blood from this and related species, report significantly higher n values at high O2 saturation. Molecular adaptive aspects are discussed.

Molecular shape, dissociation, and oxygen binding of the dodecamer subunit of Lumbricus terrestris hemoglobin

Small angle x-ray scattering of the 213-kDa dodecamer of Lumbricus terrestris Hb yielded radius of gyration = 3.74 +/- 0.01 nm, maximum diameter = 10.59 +/- 0.01 nm, and volume = 255 +/- 10 nm3, with no difference between the oxy and deoxy states. Sedimentation velocity studies indicate the dodecamer to have a spherical shape and concentration- and Ca2+-dependent equilibria with its constituent subunits, the disulfide-bonded trimer of chains a-c and chain d. Equilibrium sedimentation data were fitted best with a trimer-dodecamer model, ln K4 = 7 (association K in liters3/g3) at 1 degrees C and 4 at 25 degrees C, providing DeltaH = -20 kcal/mol and DeltaS = 4.4 eu/mol. Oxydodecamer dissociation at pH 8.0, in urea, GdmCl, heteropolytungstate K8[SiW11O39] and of metdodecamer at pH 7, was followed by gel filtration. Elution profiles were fitted with exponentially modified gaussians to represent the three peaks. Two exponentials were necessary to fit all the dissociations except in [SiW11O39]-8. Equilibrium oxygen binding measurements at pH 6.5-8. 5, provided P50 = 8.5, 11.5-11.9 and 11.9-13.5 torr, and n50 = 5.2-9. 5, 3.2-4.9, and 1.8-2.7 for blood, Hb, and dodecamer, respectively, at pH 7.5, 25 degrees C. P50 was decreased 3- and 2-fold in approximately 100 mM Ca2+ and Mg2+, respectively, with concomitant but smaller increases in cooperativity.

The crystal structures of trout Hb I in the deoxy and carbonmonoxy forms

We have determined the X-ray crystallographic structure of trout Hb I in both the deoxy and carbonmonoxy forms to resolution limits of 2.3 angstroms and 2.5 angstroms, respectively. The overall fold of the molecule is highly similar to that of human HbA despite the low level of sequence identity between these proteins. Trout Hb I is unusual in displaying almost no pH dependence of oxygen binding affinity, and (at most) very weak interactions with heterotropic effector ligands such as organic phosphates. Comparison of the two quaternary states of the protein indicates how such effects are minimised and how the low-affinity T state of the protein is stabilised in the absence of heterotropic interactions.

Oxygen equilibria of cathodic eel hemoglobin analysed in terms of the MWC model and Adair's successive oxygenation theory

Allosteric effects of erythrocytic NTP and proton concentrations on cathodic eel Hb were investigated by precise measurement of Hb-O2 equilibria (including extreme saturation values) and analysis in terms of the MWC two-state model and the Adair four-step oxygenation theory. Stripped cathodic Hb shows a reverse Bohr effect and high sensitivities to ATP and GTP that extend to high pH values (> 8.5). A decrease in pH raises KT and lowers the allosteric constant L, compared to opposite effects in 'normal' Bohr effect Hbs. Phosphates even at low concentrations (GTP/Hb = 0.5) annihilate the reverse Bohr effect. GTP exerts a greater effect than ATP due to greater changes in KT and L, and NTP slightly reduces KR. In the absence of NTP, about 1.1 protons are released on deoxygenation at pH 8.15 (where most protons are released), indicating a pK value of the reverse Bohr group of approximately 8.2 (higher in oxy-Hb and lower in deoxy-Hb). The pH and NTP dependence of the Adair association constants and calculated fractional populations of Hb molecules in different oxygenation stages show that NTP effectors stabilise the T structure and postpone the T-R transition, whereas protons in the absence of NTP have the opposite effect. A molecular mechanism for the reverse Bohr effect is suggested.

Spectroscopical and functional characterization of the hemoglobin of Nostoc commune (UTEX 584 (Cyanobacterial)

Structural analysis of a monomeric hemoglobin from the cyanobacterium Nostoc commune strain UTEX 584, cyanoglobin (Potts et al. (1992) Science 256, 1690-1692), is presented. Cyanoglobin binds molecular oxygen reversibly, with high oxygen affinity and non-cooperativity. There was no evidence for decreased stability of the pigment at 37 degrees C. Cyanoglobin-specific antibodies showed no cross-reactivity with two reference hemoglobins, leghemoglobin a and sperm whale myoglobin. The absorption spectral properties of cyanoglobin differ significantly from those of the two reference hemoglobins. The spectrum of oxy-cyanoglobin most closely resembles that of an oxy-hemoglobin from the protozoan Tetrahymena pyriformis, a hemoprotein that shares substantial amino-acid sequence identity with cyanoglobin. Met-cyanoglobin possesses spectral characteristics at pH 7.0-9.0 that resemble those of the alkaline met-hemoglobin (a putative hemichrome) of another protozoan, Paramecium caudatum. The spin-state character of met-cyanoglobin is pH-dependent. Met-cyanoglobin does not coordinate the strong-field ligands, cyanide and azide, at pH 7.0. The capacity of cyanoglobin to coordinate cyanide increased with decreasing pH. Far-UV CD spectra of cyanoglobin are indicative of a protein with a significant amount of alpha-helical structure. Data from Soret-region CD spectra suggest that the orientations of the heme moieties in cyanoglobin and leghemoglobin a are similar to one another.

Mass spectrometric composition, molecular mass and oxygen binding of Macrobdella decora hemoglobin and its tetramer and monomer subunits

The hexagonal bilayer hemoglobin (Hb) of the leech Macrobdella decora has an equilibrium sedimentation mass of 3544(+/- 80) kDa. Maximum entropy analysis of the electrospray ionization mass spectra of the Hb show three groups of peaks: two peaks of equal intensity at approximately 17 kDa, A (16,770.1 Da) and B (16,841.9 Da); three peaks at approximately 24 kDa, C (24,340.1 Da), D (24,398.6 Da) and E (24,420.0 Da) with relative intensities of 1:6:3, respectively; and three peaks of equal intensities at approximately 33 kDa, F (32,586.0 Da), G (32,714.5 Da) and H (32,849.9 Da). Although reduction with dithiothreitol does not affect the masses of peaks A through E, the approximately 33 kDa peaks give rise to four new peaks at approximately 16 kDa, P (16,052.2 Da), Q (16,537.3 Da), R (16,666.7 Da) and S (16,792.9 Da), indicating that F, G and H represent disulfide-bonded dimers of globin chains, P + Q, P + R and P + S, respectively. The relative intensities of the three groups of peaks are (A + B) to (C + D + E) to (F + G + H) = 0.39:0.26:0.32, and the globin to linker ratio 0.71:0.29 is in good agreement with the ratio 0.72:0.28 obtained by HPLC. The largest functional subunit obtained by dissociation at pH 7 in 4 M urea, is a subunit lacking linker chains with apparent mass 63(+/- 3) kDa. The equilibrium sedimentation profile of this subunit is fitted best as a monomer-dimer-tetramer equilibrium, with association constants K1,2 = 365 l g-1 and K1,4 = 8.1 x 10(5) l3 g-3. A model of the Hb consisting of a hexagonal bilayer of 36 tetramer and 42 linker subunits provides a total mass and globin to linker ratio closest to the experimental values. Equilibrium O2 binding measurements of the native Hb and its tetramer and monomer subunits were carried out over the pH range 6.6 to 8.0 at 10 and 25 degrees C, and in the absence and presence of Na+, Mg2+ and Ca2+. The Hb exhibits a moderately high O2 affinity, P50 = 4.4 torr at pH 7.5 and 25 degrees C, a high cooperativity (n50 approximately 3) and a substantial Bohr effect, phi = delta log P50/delta pH = -0.38. The tetramer subunit has a higher affinity, lower cooperativity and smaller Bohr effect, 1.9 torr, 1.3 to 1.5 and -0.30, respectively. The monomer subunit has a much higher affinity (P50 = 0.29 torr) and no cooperativity or Bohr effect.(ABSTRACT TRUNCATED AT 400 WORDS)

The cathodic hemoglobin of Anguilla anguilla. Amino acid sequence and oxygen equilibria of a reverse Bohr effect hemoglobin with high oxygen affinity and high phosphate sensitivity

As in other fish, the cathodic hemoglobin of the eel Anguilla anguilla is considered to play an important role in oxygen transport under hypoxic and acidotic conditions. In the absence of phosphates this hemoglobin shows a reverse Bohr effect and high oxygen affinity, which is strongly modulated over a side pH range by GTP (whose concentration in the red blood cells varies with ambient oxygen availability). GTP obliterates the reverse Bohr effects in the cathodic hemoglobin. The molecular basis for the reverse Bohr effect in fish hemoglobins has remained obscure due to the lack of structural data. We have determined the complete amino acid sequence of the alpha and beta chains of the cathodic hemoglobins of A. anguilla and relate it to the oxygen equilibrium characteristics. Several substitutions in crucial positions are observed compared with other hemoglobins, such as the replacement of the C-terminal His of the beta chain of Phe (that suppresses the alkaline Bohr effect) and of residues at the switch region between alpha and beta subunits (that may alter the allosteric equilibrium, thus causing the high intrinsic oxygen affinity and low cooperativity). The residues binding organic phosphate in the beta cleft of fish hemoglobins are conserved, which explains the strong effect of GTP on oxygen affinity and suggests that these residues contribute to the reverse Bohr effect in the absence of alkaline Bohr groups. Moreover, His beta 143 that is considered to be responsible for the reverse Bohr effect in human and tadpole Hbs is replaced by Lys.

The hemoglobin system of the hagfish Myxine glutinosa: aggregation state and functional properties

Hemoglobin (Hb) from the hagfish Myxine glutinosa is composed of six major monomeric subunits. Some of these subunits aggregate to dimers at low pH, and to tetramers when deoxygenated and at high protein concentration. The aggregation is inhibited by the presence of KCl. Oxygen equilibrium studies show the presence of a small Bohr effect which is strongly reduced by KCl, indicating that it originates from pH-dependent aggregation. ATP and DPG cause a similar decrease in the Bohr effect. O2 affinity is dependent on protein concentration, temperature and presence of CO2. Cooperativity is practically absent. O2 binding properties of the separated aggregating and non-aggregating Hbs purified at low pH cannot account for the functional properties of the composite hemolysate, suggesting the presence of other subunits interactions. The results are discussed in relation to literature data for other cyclostome Hbs and for M. glutinosa Hb, where the presence of three major monomeric Hbs and a possible CO2-dependent aggregation had been reported.

Hemoglobins from Plasmodium-infected rat erythrocytes: functional and molecular characteristics

Aiming to evaluate the mechanisms responsible for altered O2-transporting properties in blood of Plasmodium-infected animals, stripped (cofactor-free) hemoglobin (Hb) solutions were prepared from infected erythrocytes (IE) and noninfected erythrocytes (NIE) of rats inoculated with Plasmodium berghei bergei for functional and structural characterization. At normal intraerythrocytic pH (+/- 7.2), Hb from IE showed a higher affinity, a larger Bohr effect, and lower sensitivities to 2,3-diphosphoglycerate (DPG) and to temperature than did NIE Hb. Moreover, as judged from electrophoresis, isoelectric focusing, and gel filtration experiments, Hb from IE show changes in charge and molecular assembly. The results indicate that the higher O2 affinity and greater Bohr factors observed in IE compared with those for NIE are attributable to chemical modification of the Hb that increases its intrinsic O2 affinity and decreases its sensitivity to DPG as well as to changes in the intracellular physicochemical milieu, including reduced DPG levels.

Purification and characterization of recombinant polymeric hemoglobin P1 of Glycera dibranchiata

The apoprotein of component P1 of the polymeric fraction of the intracellular hemoglobin of the marine polychaete Glycera dibranchiata has been expressed at a high level in Escherichia coli. The expressed globin was reconstituted with heme and purified. The N-terminal sequence of the recombinant P1 is identical to the cDNA-derived sequence of cloned P1 (Zafar et al., Biochem. Biophys. Acta, 1041, 117-123, 1990). Gel filtration, SDS-PAGE, optical spectra over the range 200-650 nm, and circular dichroism over the range 200-250 nm of the purified recombinant P1 were very similar to the polymeric fraction of native Glycera hemoglobin. The molar ellipticity at 222 nm provided an estimate of 77% for the alpha-helical content of the recombinant P1, in excellent agreement with that calculated from the crystal structure of Glycera monomeric component M-II. Although the oxygen binding affinity of the recombinant P1 is higher than that of the polymeric fraction of Glycera hemoglobin (3-4 torr vs 7-13 torr), which consists of at least six different single-chain hemoglobins, the Hill coefficient is lower (1.0-1.2 vs 1.2-1.4).

Mutant hemoglobins (alpha 119-Ala and beta 55-Ser): functions related to high-altitude respiration in geese

The unusually high blood-O2 affinity in the bar-headed and Andean geese is a necessary adaptation for migration across high mountain ranges. The amino acid residues alpha-119 and beta-55, which form an alpha 1 beta 1 contact in human hemoglobin (Hb), are altered in bar-headed and Andean geese, respectively, which suggests that loss of this contact increases O2 affinity. Two mutant human Hbs with equivalent mutations at these sites prepared by site-directed mutagenesis show the same increase in O2 affinity compared with Hb A, which indicates that these mutations are responsible for the changes in the protein. The intrinsic affinity difference compared with native Hb A is amplified by organic phosphates. Whereas the recombinant and native Hbs displayed similar sensitivities to pH, chloride, and 2,3-diphosphoglycerate, the oxygenation heat of the alpha-chain mutant decreased in the presence of 2,3-diphosphoglycerate. O2 association constants for the deoxygenated state of the alpha-mutant were about three times those for Hb A. The mutant Hb analogously exhibited higher affinity constants for binding the first three O2 molecules. Calculated heme-heme interaction energies indicated that loss of a single contact, resulting in destabilization of the deoxy (tense) structure, underlies the increased O2 affinity. Adaptations securing Hb-O2 binding at extreme altitude are discussed.

Arterial blood gas tensions during breath-hold diving in the Korean ama

Korean female unassisted divers (cachido ama) breath-hold dive > 100 times to depths of 3-7 m during a work day. We sought to determine the extent of arterial hypoxemia during normal working dives and reasonable time limits for breath-hold diving by measuring radial artery blood gas tensions and pH in five cachido ama who dove to a fixed depth of 4-5 m and then continued to breath hold for various times after their return to the surface. Eighty-two blood samples were withdrawn from indwelling radial artery catheters during 37 ocean dives. We measured compression hyperoxia [arterial PO2 = 141 +/- 24 (SD) Torr] and hypercapnia (arterial PCO2 = 46.6 +/- 2.4 Torr) at depth. Mean arterial PO2 near the end of breath-hold dives lasting 32-95 s (62 +/- 14 s) was decreased (62.6 +/- 13.5 Torr). Mean arterial PCO2 reached 49.9 +/- 5.4 Torr. Complete return of these values to their baseline did not occur until 15-20 s after breathing was resumed. In dives of usual working duration (< 30 s), blood gas tensions remained within normal ranges. Detailed analysis of hemoglobin components and intrinsic oxygenation properties revealed no evidence for adaptive changes that could increase the tolerance of the ama to hypoxic or hypothermic conditions associated with repetitive diving.