The artificial oxygen carrier erythrocruorin-characteristics and potential significance in medicine

The diminishing supply and increasing costs of donated blood have motivated research into novel hemoglobin-based oxygen carriers (HBOCs) that can serve as red blood cell (RBC) substitutes. HBOCs are versatile agents that can be used in the treatment of hemorrhagic shock. However, many of the RBC substitutes that are based on mammalian hemoglobins have presented key limitations such as instability and toxicity. In contrast, erythrocruorins (Ecs) are other types of HBOCs that may not suffer these disadvantages. Ecs are giant metalloproteins found in annelids, crustaceans, and some other invertebrates. Thus far, the Ecs of Lumbricus terrestris (LtEc) and Arenicola marina (AmEc) are the most thoroughly studied. Based on data from preclinical transfusion studies, it was found that these compounds not only efficiently transport oxygen and have anti-inflammatory properties, but also can be modified to further increase their effectiveness. This literature review focuses on the structure, properties, and application of Ecs, as well as their advantages over other HBOCs. Development of methods for both the stabilization and purification of erythrocruorin could confer to enhanced access to artificial blood resources.

ERYTHROCRUORIN OF MARPHYSA SANGUINEA

1. The polychaete worm Marphysa sanguinea has a circulating erythrocruorin of mol.wt. about 2.4x10(6) (S(0) (20,w) 58.2s, D(20,w) 2.06x10(-7) cm.(2)/sec). This is the predominant form existing at pH 6-8 and (non-protein) I 0.10-0.21, and also at approx. pH 6.7 and I 0.15-3.00. 2. The pigment contains 2.24% of protohaem. 3. The 58s protein has an electrophoretic mobility of 8.08x10(-5) cm.(2)/v/sec. at pH 8.12, I 0.21 and 0 degrees . The isoelectric point of suspended particles is 4.63 at I 0.16 and 21.5 degrees . 4. At very low ionic strength and pH 6.7 (unbuffered) the 58s pigment associates reversibly to 97s and 150s forms, which are probably dimer and tetramer species. 5. At pH 10.0 and I 0.025, it dissociates irreversibly to give a small amount of 2-4s non-haem-containing protein and much 9s haem-enriched protein. These and the 58s pigment may correspond to structures found in Levin's (1963) electron-microscope studies of other erythrocruorins. 6. Absorption spectra of the 58s oxygenated erythrocruorin and the deoxygenated and carbon monoxide derivatives have been obtained.

Molecular shape of Lumbricus terrestris erythrocruorin studied by electron microscopy and image analysis

The molecular structure of erythrocruorin (hemoglobin) from Lumbricus terrestris has been studied by electron microscopy of negatively stained particles. Over 1000 molecular projections were selected from a number of electron micrographs and were then classified by multivariate statistical image-processing techniques. The two main groups of top and side views were each subdivided into smaller classes with significantly different features. About half of the top-view projections exhibit perfect hexagonal symmetry at the current resolution of about 2.0 nm, while the other top views lack this symmetry, probably as a result of tilting of the molecules relative to the carbon support film. The side views were separated into two 'families', each associated with the two different stable side-view positions the molecules can take. From these narrow stable side-views, the two families of projections are, again, generated by tilting. The symmetry properties of the three non-tilted projections show that Lumbricus erythrocruorin has a pointgroup D6 (622) symmetry rather than D3 (32).

Molecular symmetry of Lumbricus erythrocruorin

X-ray diffraction data to a minimum Bragg spacing of 5.5 A have been collected from crystals of Lumbricus terrestris erthrocruorin, a 3.9 x 10(6)-dalton respiratory protein. Self-rotation function calculations from these data reveal D6 symmetry to a resolution of at least 6 A. These calculations show that erythrocruorin molecules pack in their crystals with molecular diads coincident with crystallographic diads along the a axis. Packing constraints limit the position of the molecular center to within 40 A of x = 1/4a.

An ESR study of nitrosyl-Aplysia brasiliana myoglobin and nitrosyl annelidae Glossoscolex paulistus erythrocruorin

The nitrosyl derivatives of Annelidae Glossoscolex paulistus hemoglobin (an earth worm erythrocruorin (Ec AGp)) and Aplysia brasiliana myoglobin (Mb Apb) are studied using ESR spectroscopy. These two proteins have a quite similar ESR spectra at 100 K, but a different temperature behaviour. The temperature dependence of the nitrosyl Mb Apb spectrum is in good agreement with the Boltzmann distribution. In the case of nitrosyl-Ec AGp, the results are explained by the existence of two types of spectrum in thermodynamic equilibrium, with delta H = 9.08 kJ/mol, delta S = 47.15 J/mol and T1/2 = 193 K. There is a great similarity of the nitrosyl-Ec AGp spectra with those reported for elephant myoglobin, suggesting the presence of the same heme environment with a glutamine residue in the distal site. The pH dependence of the spectrum of nitrosyl-Mb Apb shows that the affinity of nitrosyl binding is higher at high pH (7.3) than at low pH (4.6). The ESR parameters are the same for these two pH values.

Crystals of Lumbricus erythrocruorin

Lumbricus terrestris erythrocruorin, a 3.9 X 10(6) Mr respiratory protein, has been crystallized in four different forms. Despite the high molecular symmetry apparent from images in electron micrographs, only one crystal form expresses any molecular symmetry as crystallographic symmetry. The lattice parameters provide upper limits on the molecular dimensions of 267 A X 308 A X 172 A (1 A = 0.1 nm), which agree well with dimensions obtained from electron micrographs of negatively stained molecules. We have collected diffraction data to 5.5 A from type III crystals and have begun a structural analysis.

Analysis of side-chain orientations in homologous proteins

The side-chain conformations of topologically equivalent residues in seven pairs of proteins ranging in sequence homology from 16% to 60% are compared. Both identical and mutated residues are included. For proteins with greater than 40% homology, it is found that at least 80% of the side-chain orientations of identical residues and 75% or more of the mutated residues in each pair of proteins have matching gamma atom dihedral angles (+/- 40 degrees); the comparison is not based strictly on chi 1 angles. Further, if a match is obtained at the gamma position, there is a high probability of matching for the delta atom(s) of the side-chain. For proteins with less than 25% homology the percentages are somewhat lower. Trends observed for conservative substitutions are essentially the same as those noted for mutated residues in general. Side-chain accessibility does not affect the probability of matches of identical residues; however, less accessible pairs of mutated residues have 10 to 20% higher matching probabilities than do exposed residues. Mismatches can frequently be related to large B-factors, certain types of amino acid substitutions, or the appearance of multiple minima on the side-chain potential energy surfaces and are most likely to occur for certain small residues (Ser, Thr, Val). Analysis of all the results makes possible the formulation of a set of rules for side-chain positioning in the modeling of homologous proteins.

Structural disorder in proteins. A comparison of myoglobin and erythrocruorin

The refinement of X-ray structural data gives the mean square displacements, (chi 2), at each position in the protein molecule. In order to get information on the significance of such values different refinement methods have been compared. The metmyoglobin structure was determined at 300 K and (chi 2)-values were obtained with the restrained refinement procedure in reciprocal space of Konnert and Hendrickson. A comparison with the results of Frauenfelder et al. was used for an error estimation. The inclusion of surface bound water increases the accuracy of the results but does not change the general picture. For erythrocruorin (CTT3) a refinement was performed in reciprocal space and compared with a refinement in real space performed earlier. The (chi 2)-values obtained from both procedures are similar although the reciprocal space refinement gives results which are physically more reasonable. A comparison of the disorder in myoglobin and erythrocruorin showed that the structural similarity results in a similarity in the disorder. Contacts of molecules in the crystal do not dominate the disorder although they locally influence (chi 2)-values. CTT3 shows large disorder in the heme region in contrast to myoglobin. The differences in the rigidity of the F-helix can be correlated with the oxygen affinities supporting models for O2 binding developed by Frauenfelder et al.

Quaternary structure of erythrocruorin from the nematode Ascaris suum. Evidence for unsaturated haem-binding sites

The quaternary structure of erythrocruorin from the nematode Ascaris suum was studied. The native protein had a sedimentation coefficient, at a protein concentration of 1 mg/ml, of 11.6 +/- 0.3 S and an Mr, as determined by sedimentation equilibrium, of 332,000 +/- 17,000. SDS/polyacrylamide-gel electrophoresis gave one band with a mobility corresponding to an Mr of 43,000 +/- 2000. The Mr of the polypeptide chain was determined to be 41,600 +/- 1,500 by sedimentation equilibrium in 6 M-guanidinium chloride and 0.1 M-2-mercaptoethanol. Cross-linking with glutaraldehyde followed by SDS/polyacrylamide-gel electrophoresis yielded a maximal number of eight bands. The haem content of Ascaris erythrocruorin was observed to vary from one preparation to another. This finding was shown to be due to non-realization of the full binding capacity for haem. By titration with haemin, the haem content was found to attain a maximal value of 2.86 +/- 0.14%, corresponding to a minimal Mr per haem group of 21,000 +/- 1,000. Our findings indicate that Ascaris suum erythrocruorin is composed of eight identical polypeptide chains, carrying two haem sites each.

[Rotation isomerization of side chains of globular proteins and its effect on the x-ray scattering curves of proteins in a solution]

A new method has been developed for averaging the intensity of X-ray diffuse scattering of proteins by different conformations of side groups. The method is based on the algorithm allowing to calculate statistical weights of rotation isomers of side chains. It is shown that for protein structures obtained from high resolution crystallographic data, conformations of the majority of surface groups correspond to rotation isomers with the greatest statistical weight. It has been found that for medium size proteins (with molecular weight varying from 15,000 to 30,000 dalton) whose structure has been determined at high resolution, the influence of rotation isomerization of side chains on the scattering indicatrices does not exceed 5%. The influence of side chains mobility on the scattering curves of large proteins is also small. For these two classes of proteins the rotation isomerization of side groups can be ignored when interpreting significant (exceeding 10%) divergences between experimental and theoretical scattering curves.

Assembly of erythrocruorin from the earthworm Octolasium complanatum

The spontaneous assembly of the earthworm erythrocruorin molecule (60 S) from its 1/12 subunits (10 S) obtained by alkaline dissociation is a long debated problem, since the 60 S to 10 S dissociation step has been regarded as essentially irreversible or as only partially reversible when freshly dissociated solutions are used. Erythrocruorin from the earthworm Octolasium complanatum has been reassembled from its 10 S subunits. "Age" of the subunits, pH, and divalent cation concentration are the factors that influence the assembly reaction. Of primary importance is the age of the subunits, i.e. their exposure time to the alkaline dissociating pH. Parallel sedimentation velocity and sodium dodecyl sulfate/polyacrylamide gel electrophoresis experiments on the dissociated and reassembled solutions indicate that two processes take place at alkaline pH values: disulfide exchange and limited proteolysis. These processes, whose relative importance differs in the various preparations, might be responsible for the loss of reassociating capacity of the 10 S subunits. With freshly dissociated subunits, reassembly up to 80% may be achieved at pH 6.2 to 6.5 in the absence of divalent cations; the presence of 25 to 50 mM-Ca2+ renders the reaction essentially pH-independent in the range 6.2 to 8. The effect of Ca2+ is discussed in the light of the presence of structure-stabilizing binding sites for divalent cations at the 10 S intersubunit's contact regions.

Erythrocruorin from the water-flea Daphnia magna. Quaternary structure and arrangement of subunits

The subunit structure of erythrocruorin from the cladoceran Daphnia magna was studied. The native protein was found to have a sedimentation coefficient (S2(20), w) of 17.9 +/- 0.2 S and a molecular weight, as determined by sedimentation equilibrium, of 494 000 +/- 33 000. Iron and haem determinations gave 0.312 +/- 0.011% and 3.84 +/- 0.04%, corresponding to minimal molecular weights of 17900 +/- 600 and 16 100 +/- 200 respectively. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis gave one band with mobility corresponding to a molecular weight of 31 000 +/- 1 500. The molecular weight of the polypeptide chain determined by sedimentation equilibrium in 6 M-guanidinium chloride and 0.1 M-2-mercaptoethanol is 31 100 +/- 1300. On a molecular-weight basis, Daphnia erythrocruorin is composed of 16 identical polypeptide chains carrying two haem groups each. The native structure is stable between pH5 and 8.5. At alkaline and acidic pH, a gradual decrease in the sedimentation coefficient down to 9.8S occurs. Above pH 10 and below pH4, a slow component with S20, w between 2.7S and 4.0S is observed. The 2.7S, 4.0S and 9.8S species are identified as single-chain subunits, subunit dimers and half-molecules respectively. We propose a model for the molecule composed of 16 2.7S subunits grouped in two layers stacked in an eclipsed orientation, the eight subunits of each layer occupying the vertices of a regular eight-sided polygon. Support for this arrangement is provided from electron microscopy and from analysis of the pH-dissociation pattern.

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.

Erythrocruorin from the crustacean Caenestheria inopinata. Quaternary structure and arrangement of subunits

The subunit structure of erythrocruorin from the crustacean Caenestheria inopinata was studied. The native protein was found to have a sedimentation coefficient of 12.0 S and a molecular weight, as determined by sedimentation equilibrium, of 302,000. Iron and heme determinations gave 0.346 and 3.98% corresponding to minimal molecular weights of 16,100 and 15,500, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis gave one band with mobility corresponding to a molecular weight of 30,000. The molecular weight of the polypeptide chain was determined to be 30,500 by sedimentation equilibrium in 6 M guanidine hydrochloride and 0.1 M 2-mercaptoethanol. Dissociation of the 12S molecule was observed at acidic and alkaline pH. A dissociation species of 2.7 S was isolated and its molecular weight determined to be 28,000 by sedimentation equilibrium. On a molecular weight basis, the native molecule is composed of ten 2.7S subunits, each of which consists of a single polypeptide chain carrying two hemes. We propose a model for the molecule composed of ten spheres, each representing a 2.7S subunit, arranged in two layers stacked in an eclipsed orientation, in five spheres of each layer occupying the vertices of a regular pentagon. Support for this arrangement is provided by a comparison of projections of the model with molecular profiles seen in the electron microscope.

[Hemoglobins XL: Sequence analysis of the monomeric hemoglobin CTT IV (erythrocruorin) of Chironomus thummi thummi, Diptera (author's transl)]

The sequence analysis of the monomeric hemoglobin CTT IV is given. The primary structure was determined by automatic Edman degradation of the protein and of peptides obtained by enzymatical or by chemical cleavages. The protein chain consists of 136 amino acids. The primary structure is compared with the primary structure of the human beta-chains and of the monomeric hemoglobin CTT III.

[Hemoglobins, XXXIX. Amino acid sequence of a dimeric hemoglobin (erythrocruorin) from Chironomus thummi thummi: component CTT VIII]

The globin of the homo-dimeric hemoglobin CTT VIII was isolated by chromatography of the CTT-hemoglobins on DEAE-cellulose and rechromatography of the crude CTT VIII globin on CM-cellulose. The sequence was established by automatic degradation of the globin, tryptic peptides derived from various limited tryptic digestions and one cyanogen bromide peptide. As an additional proof of the C-terminal sequence splitting with carboxypeptidase was carried out. The tryptic activity was limited by chemical modification of the epsilon-amino groups of the lysines nd the delta-guanidino groups of the arginines, respectively. A reduction of the tryptic fragments from the maleylated globin was achieved by special digestion conditions: high pH value and short digestion time. The hemoglobin consists of 2 X 151 residues with a molecular weight of 32438. The structure of CTT VIII is homologously aligned with a monomeric CTT-hemoglobin (CTT III) and the human-beta-chain. There is a conformity of 39.7% to the CTT III-hemoglobin and 13.9% to the human beta-chains. All three hemoglobins are identical in 12 positions only. The secondary structures are postulated according to the CTT III-component. Possible structural differences are discussed.

Hemoglobins, XXXVIII. Amino acid sequence of a dimeric hemoglobin (erythrocruorin), component VI from Chironomus thummi thummi (CTT VI)

The dimeric hemoglobin CTT VI (Erythrocruorin) was isolated from the hemolymph of the larvae of Chironomus thummi thummi. The globin from CTT VI was subjected to trypsin, limited trypsin and cyanogen bromide digestion. For elucidation of the sequence in the C-terminal region, cleavage with Staphylococcus aureus V8 protease was also carried out. The peptides were separated by gel and ion-exchange chromatography. The handling of some large fragments was facilitated by maleylation and subsequent ion-exchange chromatography with conservation of the maleyl groups. The amino acid sequence was determined by automatic Edman degradation. The order of the peptides was provided by overlaps, but in two cases by homology only (for residues 98 and 99, and 109 and 110). The hemoglobin consists of 2 x 147 amino acids with a molecular weight of 32411. The sequence of CTT VI is compared with a monomeric (CTT III) and a dimeric hemoglobin (CTT II beta) and the human alpha-chains. The structural differences are discussed.

[Method for calculation of low-energy conformations of alpha-helical pairs of globular proteins]

The computer model of folding of two alpha-helices of globular proteins was developed. The radicals of amino acids were approximated by spheres with centers located in C beta-atoms. The functional of energy took into account the hydrophobic interactions of alpha-helices, electrostatic contacts of charged and polar side groups of amino acid, Van der Waals' interactions. The conformations with minimum energies of two-helical superstructures G--H from alpha- and beta-chains of horse hemoglobin, sperm whale myoglobin, and erythrocruorin were computed. They have mean deviation 0.7--1.8 A from native conformations of these proteins. Hence, at the self-organization process alpha-helices firstly are "roughly" oriented by hydrophobic interactions, but the choice of stable conformation occurs by Van der Waals' and electrostatic interactions. On this stage the low-energy conformation becomes "frozen" and cannot be significantly rearranged later. The mutual orientation of secondary protein structures are determined mainly by amino acid radical volumes, their hydrophobicity and charge.

[Hemoglobins, XXXVII. The primary structure of a monomeric insect hemoglobin (Erythrocruorin), component CTT IIIa of Chironomus thummi thummi. An anomalous Heme complex: E7 Gln, E11 Ile]

The primary structure of the monomeric hemoglobin CTT IIIa of the midge larva of Chironomus thummi thummi is presented. Cyanogenbromide peptides and tryptic peptides were used for sequence analysis. The primary structure was established with a small number of large peptides. The complete sequencing of the cyanogen bromide peptides was enabled by the C-terminal fixation of arginine. The primary structure of CTT IIIa is compared to the beta-chains of human and to the monomeric component CTT III: CTT IIIa possesses a "tail" of 9 amino acids on the N-terminus, and shows only a small number of identical residues compared to the number that other CTT hemoglobins share with each other. Also the heme complex is unusual: E7 Gln and E11 Ile.

[Hemoglobins, XXXVI: The primary structure of a dimeric insect hemoglobin (Erythrocruorin), component IX from Chironomus thummi thummi. Studies on the quarternary structure of the dimeric CTT-hemoglobins (author's transl)]

The primary structure of a dimeric insect hemoglobin (erythrocruorin), component CTT IX (Chironomus thummi thummi) was established by automatic sequence analysis. The alignment of the peptides was facilitated by producing only a few large fragments. The primary structure of CTT IX is compared with the human beta-chains and with CTT III. It is discussed, why for the dimeric CTT-hemoglobins only dimerisation can be observed but no tetramerisation. Experiments were done to locate the binding areas between the subunits in the dimeric molecule. Even after blocking of the alpha-NH2-group by cyanate, the stability of the dimeric molecule is not altered. Therefore the binding regions of the CTT-hemoglobins must be different from those of the tetrameric hemoglobins of vertebrates. Our results lead to a quarternary structure different from that of the hemoglobins of mammalians. This structure explains the possibility of dimerisation, but excludes tetramerisation.

The primary structure of the monomeric hemoglobin (erythrocruorin) component CTT IV of Chironomus thummi thummi (Insecta, Diptera)

The primary structure of the monomeric hemoglobin (Erythrocruorin) CTT IV from larvae of Chironomus thummi thummi (Diptera) is presented. The sequence was determined automatically. The primary structure is compared with human alpha-globin-chain.

Some aspects concerning conformation of polypeptide chains in proteins

The structure of (S)-N,N'-di-tert-butyl-2-[N-(1-phenylethyl)benzamido] malonamide contains two fragments of a polypeptide chain. This compound therefore can be taken as a model substance for details of protein conformation. In the crystalline state one peptide chain of the model molecule incorporates a hydrogen bond between two adjacent nitrogen atoms in the backbone. The acceptor for the hydrogen is the pz-orbital at the proton accepting nitrogen. The occurence of such hydrogen bonds in proteins might explain some correlations found between phi and psi torsion angles. In addition a correlation between torsion angle /psi/ and the bond angle tau at C alpha in the backbone of polypeptide chains could be established. The model substance also contains a "frozen" back side attack of a C = O group on the tetrahydrally coordinated C alpha in analogy to the SN2 substitution reaction of the Walden inversion with a trigonal bipyramidal transition state.

Amphitrite ornata erythrocruorin. I. Structural properties and characterization of subunit interactions

A high molecular weight erythrocruorin (Mr approx. 3 . 10(6)) is found in the vascular system of the marine terebellid worm Amphitrite ornata, while a low molecular weight hemoglobin is contained in the coelomic cells. Polyacrylamide gel electrophoresis indicates that Amphitrite erythrocruorin contains three different types of polypeptide chain, of molecular weight approx. 15,000, whereas the molecular weight per heme group is approx. 20,000. These data suggest that only two of three polypeptide chains may be associated with a heme group. The coelomic hemoglobin, which occurs as a monomer, has an apparent molecular weight of approx. 14,000. The circular dichroism spectra of Amphitrite erythrocruorin and of the coelomic protein reveal marked differences in the heme environment, while the alpha-helical contents are not very different (60% and 70%, respectively). Amphitrite erythrocruorin is unusual in its dissociation behavior. Divalent cations are required for maintaining the quaternary structure. In the pH range 7.75--8.5, when the Ca2+ concentration is reduced below 1 mM, the whole molecule (57 S) dissociates into a number of lower molecular weight species (25, 15, 10 and 3 S) which have been correlated with specific subunit structures by electron microscopy. Whole molecules and 25 S subunits are not in equilibrium with the lower molecular weight species and can be isolated from partially dissociated mixtures. In contrast, the lower molecular weight subunits are themselves in a state of rapid equilibrium which is sensitive to cations, protons and oxygen. Of special interest is the dimerization reaction of the 10 S subunits, which appears to be mediated by Ca2+ and conforms to the predictions of the Cann and Goad theory on ligand mediated equilibria. The dissociation of Amphitrite erythrocruorin is readily reversible when the Ca2+ concentration is increased. The subunits obtained at physiological (7.8) or slightly acid (6.5) pH completely reassemble into whole molecules. Reassembly, however, is only partial when dissociation occurs at high pH. The presence of stable intermediates, such as the 15 S species, may facilitate the reassociation process.

Molecular architecture of annelid erythrocruorins. Extracellular hemoglobin of Arenicola marina (Polychaeta)

The respiratory protein, erythrocruorin, of the annelid Arenicola marina was investigated. Spectral properties show many analogies with those of vertebrate hemoglobine. 144 heme groups (ferroprotoporphyrin) were found in the whole molecule, which has a relative molecular mass of 3.56 X 10(6), as determined by sedimentation equilibrium, and an isoelectric point of 4.69. Protein dissociation patterns were analysed by electrophoresis after denaturation in the presence of dodecylsulfate, with and without 2-mercaptoethanol. A tentative model associating molecular mass of the native molecule, heme content, molecular mass of the polypeptide chains and functional properties is proposed. A twelfth subunit of A. marina erythrocruorin would contain twelve heme groups arranged in three functional units made up of four protomers, half of these being covalently bound to non-heme chains; two structural chains would be spatially arranged as bonds between the subunits.

Subunit structure of erythrocruorin from the polychaete Tylorrhynchus heterochaetus

Sodium dodecyl sulfate (SDS)-gel electrophoresis of erythrocruorin from the polychaete Tylorrhynchus heterochaetus revealed the presence of four subunits with molecular weights of 12,000, 22,000, 23,500, and 54,000 in a molar ratio of 6 : 1 : 2 : 3, respectively. The largest subunit dissociates into polypeptide chains of 13,500 molecular weight in the presence of mercaptoethanol, whereas each of the other subunits consists of a single polypeptide chain. Hemochromogen determination gave a minimum molecular weight of 26,500 per mol of heme group. A model of the subunit structure of the erythrocruorin molecule is proposed, composed of 144 subunits (252 polypeptide chains) possessing 144 heme groups. The molecular weight of the erythrocruorin was calculated to be 3.636 x 10(6).

[The primary structure of a dimeric hemoglobin (erythrocruorin); component CTT VI of Chironomus thummi thummi, Diptera (author's transl)]

The complete amino acid sequence of 147 residues was determined automatically for a major dimeric component (CTT VI) of the insect larva Chironomus thummi thummi (Diptera). The molweight was found to be 32411. All tryptic, maleylated tryptic and cyanogen bromide peptides were isolated. The handling of some large fragments was facilitated by maleylation and subsequent ion exchange chromatography. Some details of the primary structure are discussed. The alignment of the amino acid sequence with that of human alpha-chains shows only 29 identical positions.

[The sequence of a dimeric hemoglobin (erythrocruorin), component IX, from Chironomus thummi thummi (Insecta Diptera) (author's transl)]

The primary structure of the dimeric hemoglobin (erythrocruorin) CTT-IX from the insect larva Chironomus thummi thummi (Insecta Diptera) is given. The sequence was determined automatically. The primary structure is compared with human alpha-chains.

[Hemoglobins. XXVI. Analysis of the primary structure of the dimeric insect haemoglobin CTT VIIB (Erythrocruorin) from Chironomus thummi thummi, Diptera]

The dimeric haemoglobin CTT VIIB (Erythrocruorin) of Chironomus thummi thummi, Diptera, has been sequenced. Either globin or globin with maleic acid blocked lysines were cleaved with trypsin. The separation of peptides and the sequence analysis are given in detail.

[Hemoglobins, XXV. Hemoglobin (erythrocruorin) CTT III from Chironomus thummi thummi (Diptera). Primary structure and relationship to other heme proteins (author's transl)]

The amino acid sequence analysis of hemoglobin (erythrocruorin) CTT III from Chironomus thummi th. (Diptera) has been checked with automatic methods and completed. The protein chain consists of 136 amino acids and contains a neutral exchange isoleucine/threonine in position 57. The molecular weight of the heme protein (Thr) is 15400. The primary structure gives the chemical basis for the refinement of the X-ray structure and the understanding of the mechanism of the Bohr effect in this monomeric hemoglobin. A homologous alignment to vertebrate globins is reported. The resulting data for the phylogeny of proto-and deuterostomian animals and the function of this hemoglobin are discussed.

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.

Ligand-dependent Bohr effect of Chrionomus hemoglobins

The O2 and CO Bohr effects of monomeric and dimeric hemoglobins of the insect Chironomus thummi thummi were determined as proton releases upon ligation. For the O2 Bohr effect of the monomeric hemoglobin III a maximum value of 0.20 H+/heme was obtained at pH 7.5. Upon ligation with CO, however, only 0.04 H+/heme were released at the same pH. In agreement with this finding isoelectric focusing experiments revealed different isoelectric points for O2-liganded and CO-liganded states of hemoglobin III. Analogous results were obtained in the cases of the monomeric hemoglobin IV and the dimeric hemoglobins of Chironomus thummi thummi; here O2 Bohr effects of 0.43 and 0.86 H+/heme were observed. For the corresponding CO Bohr effects values of 0.08 and 0.31 H+/heme were obtained respectively. On the basis of the available structural data the reduced CO Bohr effect in hemoglobin III is discussed as arising from a steric hindrance of the CO ligand by the side chain of isoleucine-E11, obstructing the movement of the heme-iron upon reaction with carbon monoxide. It should, however, be noted that ligands, according to their different electron donor and acceptor properties, may generally induce different conformational changes and thus different Bohr effects, in those hemoglobins in which distinct tertiary and/or quaternary constraints have not evolved. The general utilization of CO instead of O2 as allosteric effector is ruled out by the results reported here.

Inequivalent conformational response of Chironomus hemoglobins to ligation with O2 and CO. A circular-dichrosim and infrared-spectroscopic study

For the monomeric hemoglobins III and IV and the dimeric hemoglobins of Chironomus the tryptophan circular dichrosim reports different conformational response to binding of different ligands. The fine structure bands at 292 nm are most strongly developed in the unliganded state and considerably reduced in the oxy form. The spectrum of the CO derivative is intermediate but clearly more deoxy-like. This finding correlates well with the corresponding Bohr effect magnitudes determined by measuring proton release upon ligation. Infrared difference spectroscopy on O2 versus CO derivatives in aqueous solution shows a normal O2 stretching band position at 1107 cm-1 characteristic of asymmetric oxygen binding. The CO stretching band, however, is consistently blue-shifted by 11--13 cm-1 from the 1951 cm-1 position observed with mammalian hemoglobins, indicating reduced CO binding strength. Structural factors relevant to an explanation of the observed phenomena are discussed.