Haemoglobin of Gastrophilus larvae. Purification and properties

Major differences in the larval anatomy of the digestive and excretory systems of three Oestridae species revealed by micro-CT

Oestrid flies (Diptera: Oestridae) do not feed during the adult stage, so they depend on an efficient assimilation and storage of nutrients during their parasitic larval stage. We describe the general morphology and provide volumetric data for the digestive and excretory organs of the three larval instars of the nasal bot fly Oestrus ovis L., using micro-computed tomography. The size of the digestive and excretory organs greatly increased across larval instars. In all instars, the two salivary glands were remarkably large and formed a 'glandular band' by coming together, but without lumina uniting, at their posterior ends. The distal region of the anterior Malpighian tubules was greatly enlarged and full of highly radio-opaque concretions. Moreover, the anatomy of O. ovis third-instar larva was compared to that of two species of, respectively, similar and different feeding habits: Cephenemyia stimulator (Clark) and Hypoderma actaeon Brauer. Whereas the general morphology and arrangement of the digestive and excretory systems of C. stimulator was similar to that of O. ovis, some differences were observed in H. actaeon: a swollen anterior region of the midgut, salivary glands shorter and not forming a 'band' and anterior Malpighian tubules narrowly uniform throughout their entire length.

The Globin Gene Family in Arthropods: Evolution and Functional Diversity

Globins are small heme-proteins that reversibly bind oxygen. Their most prominent roles in vertebrates are the transport and storage of O₂ for oxidative energy metabolism, but recent research has suggested alternative, non-respiratory globin functions. In the species-rich and ecologically highly diverse taxon of arthropods, the copper-containing hemocyanin is considered the main respiratory protein. However, recent studies have suggested the presence of globin genes and their proteins in arthropod taxa, including model species like Drosophila. To systematically assess the taxonomic distribution, evolution and diversity of globins in arthropods, we systematically searched transcriptome and genome sequence data and found a conserved, widespread occurrence of three globin classes in arthropods: hemoglobin-like (HbL), globin X (GbX), and globin X-like (GbXL) protein lineages. These globin types were previously identified in protostome and deuterostome animals including vertebrates, suggesting their early ancestry in Metazoa. The HbL genes show multiple, lineage-specific gene duplications in all major arthropod clades. Some HbL genes (e.g., Glob2 and 3 of Drosophila) display particularly fast substitution rates, possibly indicating the evolution of novel functions, e.g., in spermatogenesis. In contrast, arthropod GbX and GbXL globin genes show high evolutionary stability: GbXL is represented by a single-copy gene in all arthropod groups except Brachycera, and representatives of the GbX clade are present in all examined taxa except holometabolan insects. GbX and GbXL both show a brain-specific expression. Most arthropod GbX and GbXL proteins, but also some HbL variants, include sequence motifs indicative of potential N-terminal acylation (i.e., N-myristoylation, 3C-palmitoylation). All arthropods except for the brachyceran Diptera harbor at least one such potentially acylated globin copy, confirming the hypothesis of an essential, conserved globin function associated with the cell membrane. In contrast to other animals, the fourth ancient globin lineage, represented by neuroglobin, appears to be absent in arthropods, and the putative arthropod orthologs of the fifth metazoan globin lineage, androglobin, lack a recognizable globin domain. Thus, the remarkable evolutionary stability of some globin variants is contrasted by occasional dynamic gene multiplication or even loss of otherwise strongly conserved globin lineages in arthropod phylogeny.

Transcriptomes reveal expression of hemoglobins throughout insects and other Hexapoda

Insects have long been thought to largely not require hemoglobins, with some notable exceptions like the red hemolymph of chironomid larvae. The tubular, branching network of tracheae in hexapods is traditionally considered sufficient for their respiration. Where hemoglobins do occur sporadically in plants and animals, they are believed to be either convergent, or because they are ancient in origin and their expression is lost in many clades. Our comprehensive analysis of 845 Hexapod transcriptomes, totaling over 38 Gbases, revealed the expression of hemoglobins in all 32 orders of hexapods, including the 29 recognized orders of insects. Discovery and identification of 1333 putative hemoglobins were achieved with target-gene BLAST searches of the NCBI TSA database, verifying functional residues, secondary- and tertiary-structure predictions, and localization predictions based on machine learning. While the majority of these hemoglobins are intracellular, extracellular ones were recovered in 38 species. Gene trees were constructed via multiple-sequence alignments and phylogenetic analyses. These indicate duplication events within insects and a monophyletic grouping of hemoglobins outside other globin clades, for which we propose the term insectahemoglobins. These hemoglobins are phylogenetically adjacent and appear structurally convergent with the clade of chordate myoglobins, cytoglobins, and hemoglobins. Their derivation and co-option from early neuroglobins may explain the widespread nature of hemoglobins in various kingdoms and phyla. These results will guide future work involving genome comparisons to transcriptome results, experimental investigations of gene expression, cell and tissue localization, and gas binding properties, all of which are needed to further illuminate the complex respiratory adaptations in insects.

Postmortem examination (2016-2017) of weanling and older horses for the presence of select species of endoparasites: Gasterophilus spp., Anoplocephala spp. and Strongylus spp. in specific anatomical sites

Parasite infections are more quantifiable postmortem than antemortem in horses. Thus a study was carried out examining dead horses for specific parasite species. Most of the weanling and older horses submitted to the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) for postmortem examination between November 22, 2016 and March 23, 2017 were examined for certain species of internal parasites. The stomach and duodenum from 69 horses were examined for bots (Gasterophilus spp.). Combined data for both Thoroughbred and non-Thoroughbred (16 other than Thoroughbred breeds/mixed breeds) horses revealed that the prevalence of Gasterophilus intestinalis was 19% (n=12) with 2nd instars (x̄ 8.5) and 39% (n=27) with 3rd instars (x̄ 90). The prevalence of Gasterophilus nasalis was 1.5% (n=1) for 2nd instars (x̄ 1) and 7% (n=5) for 3rd instars (x̄ 25). A few third instar G. intestinalis placed in 10% formalin showed slight movement at over two hundred hours later. The cecum and about 25cm of the terminal part of the ileum were examined from 139 horses for tapeworms (Anoplocephala spp.) and large strongyles (Strongylus spp.). The prevalence of A. perfoliata was 44% (n=62) and the average number of specimens per infected horse was 92.5. Strongylus vulgaris and Strongylus edentatus were not found in the gut of any horse.

Biological signaling by carbon monoxide and carbon monoxide-releasing molecules

Carbon monoxide (CO) is continuously produced in mammalian cells during the degradation of heme. It is a stable gaseous molecule that reacts selectively with transition metals in a specific redox state, and these characteristics restrict the interaction of CO with defined biological targets that transduce its signaling activity. Because of the high affinity of CO for ferrous heme, these targets can be grouped into heme-containing proteins, representing a large variety of sensors and enzymes with a series of diverse function in the cell and the organism. Despite this notion, progress in identifying which of these targets are selective for CO has been slow and even the significance of elevated carbonmonoxy hemoglobin, a classical marker used to diagnose CO poisoning, is not well understood. This is also due to the lack of technologies capable of assessing in a comprehensive fashion the distribution and local levels of CO between the blood circulation, the tissue, and the mitochondria, one of the cellular compartments where CO exerts its signaling or detrimental effects. Nevertheless, the use of CO gas and CO-releasing molecules as pharmacological approaches in models of disease has provided new important information about the signaling properties of CO. In this review we will analyze the most salient effects of CO in biology and discuss how the binding of CO with key ferrous hemoproteins serves as a posttranslational modification that regulates important processes as diverse as aerobic metabolism, oxidative stress, and mitochondrial bioenergetics.

Knockdown of Drosophila hemoglobin suggests a role in O2 homeostasis

Almost all insects are equipped with a tracheal system, which appears to be sufficient for O2 supply even in phases of high metabolic activity. Therefore, with the exception of a few species dwelling in hypoxic habitats, specialized respiratory proteins had been considered unnecessary in insects. The recent discovery and apparently universal presence of intracellular hemoglobins in insects has remained functionally unexplained. The fruitfly Drosophila melanogaster harbors three different globin genes (referred to as glob1-3). Glob1 is the most highly expressed globin and essentially occurs in the tracheal system and the fat body. To better understand the functions of insect globins, the levels of glob1 were modulated in Drosophila larvae and adults by RNAi-mediated knockdown and transgenic over-expression. No effects on the development were observed in flies with manipulated glob1 levels. However, the knockdown of glob1 led to a significantly reduced survival rate of adult flies under hypoxia (5% and 1.5% O2). Surprisingly, the glob1 knockdown flies also displayed increased resistance towards the reactive oxygen species-forming agent paraquat, which may be explained by a restricted availability of O2 resulting in decreased formation of harmful O2(-). In summary, our results suggest an important functional role of glob1 in O2 homeostasis, possibly by enhancing O2 supply.

Evolution of Respiratory Proteins across the Pancrustacea

Respiratory proteins enhance the capacity of the blood for oxygen transport and support intracellular storage and delivery of oxygen. Hemocyanin and hemoglobin are the respiratory proteins that occur in the Pancrustacea. The copper-containing hemocyanins evolved from phenoloxidases in the stem lineage of arthropods. For a long time, hemocyanins had only been known from the malacostracan crustaceans but recent studies identified hemocyanin also in Remipedia, Ostracoda, and Branchiura. Hemoglobins are common in the Branchiopoda but have also been sporadically found in other crustacean classes (Malacostraca, Copepoda, Thecostraca). Respiratory proteins had long been considered unnecessary in the hexapods because of the tracheal system. Only chironomids, some backswimmers, and the horse botfly, which all live under hypoxic conditions, were known exceptions and possess hemoglobins. However, recent data suggest that hemocyanins occur in most ametabolous and hemimetabolous insects. Phylogenetic analysis showed the hemocyanins of insects and Remipedia to be similar, suggesting a close relationship of these taxa. Hemocyanin has been lost in dragonflies, mayflies, and Eumetabola (Hemiptera + Holometabola). In cockroaches and grasshoppers, hemocyanin expression is restricted to the developing embryo while in adults oxygen is supplied solely by the tracheal system. This pattern suggests that hemocyanin was the oxygen-transport protein in the hemolymph of the last common ancestor of the pancrustaceans. The loss was probably associated with miniaturization, a period of restricted availability of oxygen, a change in life-style, or morphological changes. Once lost, hemocyanin was not regained. Some pancrustaceans also possess cellular globin genes with uncertain functions, which are expressed at low levels. When a respiratory protein was again required, hemoglobins evolved several times independently from cellular globins.

Developmental changes in hypoxic exposure and responses to anoxia in Drosophila melanogaster

Holometabolous insects undergo dramatic morphological and physiological changes during ontogeny. In particular, the larvae of many holometabolous insects are specialized to feed in soil, water or dung, inside plant structures, or inside other organisms as parasites where they may commonly experience hypoxia or anoxia. In contrast, holometabolous adults usually are winged and live with access to air. Here we show that larval Drosophila experience severe hypoxia in their normal laboratory environments; third instar larvae feed by tunneling into a medium without usable oxygen. Larvae move strongly in anoxia for many minutes, while adults (like most other adult insects) are quickly paralyzed. Adults survive anoxia nearly an order of magnitude longer than larvae (LT50: 8.3 vs. 1 h). Plausibly, the paralysis of adults is a programmed response to reduce ATP need and enhance survival. In support of that hypothesis, larvae produce lactate at 3x greater rates than adults in anoxia. However, when immobile in anoxia, larvae and adults were similarly able to decrease their metabolic rate in anoxia, to about 3% of normoxic conditions. These data suggest that Drosophila larvae and adults have been differentially selected for behavioral and metabolic responses to anoxia, with larvae exhibiting vigorous escape behavior likely enabling release from viscous anoxic media to predictably normoxic air, while the paralysis behavior of adults maximizes chances of survival of flooding events of unpredictable duration. Developmental remodeling of behavioral and metabolic strategies to hypoxia/anoxia is a previously unrecognized major attribute of holometabolism.

Molecular and functional characterization of hemocyanin of the giant African millipede, Archispirostreptus gigas

In contrast to other terrestrial arthropods where gaseous O2 that fuels aerobic metabolism diffuses to the tissues in tracheal tubes, and most other metazoans where O2 is transported to tissues by circulating respiratory proteins, the myriapods (millipedes and centipedes) strikingly have tracheal systems as well as circulating hemocyanin (Hc). In order to elucidate the evolutionary origin and biological significance of millipede Hc we report the molecular structure (subunit composition and amino acid sequence) of multimeric (36-mer) Hc from the forest-floor dwelling giant African millipede Archispirostreptus gigas and its allosteric oxygen binding properties under various physico-chemical conditions. A. gigas Hc consists of only a single subunit type with differential glycosylation. Phylogenic analysis reveals that millipede Hc is a sister group to centipede HcA, which supports an early divergence of distinct Hc subunits in myriapods and an ancient origin of multimeric Hcs. A. gigas Hc binds O2 with a high affinity and shows a strong normal Bohr effect. O2 binding is moreover modulated by Ca2+ ions, which increase the O2 affinity of the Hc in the T (tense; deoxygenated) as well as the R (relaxed; oxygenated) states, and by (L)-lactate, which modulates Hc-O2 affinity by changing the allosteric equilibrium constant, L. Cooperativity in O2-binding at half O2-saturation (n50) is pH-dependent and maximal at pH ~7.4 and the number of interacting O2 binding sites (q) is markedly increased by binding Ca2+. The data is discussed in the light of the role of mutually supplementary roles of Hc and the tracheal system for tissue O2 supply.

Characterization of the hemoglobin of the backswimmer Anisops deanei (Hemiptera)

While O(2)-binding hemoglobin-like proteins are present in many insects, prominent amounts of hemoglobin have only been found in a few species. Backswimmers of the genera Anisops and Buenoa (Notonectidae) have high concentrations of hemoglobin in the large tracheal cells of the abdomen. Oxygen from the hemoglobin is delivered to a gas bubble and controls the buoyant density, which enables the bugs to maintain their position without swimming and to remain stationary in the mid-water zone where they hunt for prey. We have obtained the cDNA sequences of three Anisops deanei hemoglobin chains by RT-PCR and RACE techniques. The deduced amino acid sequences show an unusual insertion of a single amino acid in the conserved helix E, but this does not affect protein stability or ligand binding kinetics. Recombinant A. deanei hemoglobin has an oxygen affinity of P(50) = 2.4 kPa (18 torr) and reveals the presence of a dimeric fraction or two different conformations. The absorption spectra demonstrate that the Anisops hemoglobin is a typical pentacoordinate globin. Phylogenetic analyses show that the backswimmer hemoglobins evolved within Heteroptera and most likely originated from an intracellular hemoglobin with divergent function.

Testes-specific hemoglobins in Drosophila evolved by a combination of sub- and neofunctionalization after gene duplication

BACKGROUND

For a long time the presence of respiratory proteins in most insects has been considered unnecessary. However, in recent years it has become evident that globins belong to the standard repertoire of the insect genome. Like most other insect globins, the glob1 gene of Drosophila melanogaster displays a conserved expression pattern in the tracheae, the fat body and the Malpighian tubules.

RESULTS

Here we show that the recently discovered D. melanogaster globin genes glob2 and glob3 both display an unusual male-specific expression in the reproductive tract during spermatogenesis. Both paralogs are transcribed at equivalent mRNA levels and largely overlap in their cellular expression patterns during spermatogenesis. Phylogenetic analyses showed that glob2 and glob3 reflect a gene duplication event that occurred in the ancestor of the Sophophora subgenus at least 40 million years ago. Therefore, flies of the Drosophila subgenus harbor only one glob2/3-like gene.

CONCLUSIONS

Phylogenetic and sequence analyses indicate an evolution of the glob2 and glob3 duplicates by a combination of sub- and neofunctionalization. Considering their restricted, testes-specific expression, an involvement of both globins in alleviating oxidative stress during spermatogenesis is conceivable.

Purification and properties of haemoglobin from Gastrothylax crumenifer (Trematode:Paramphistomatidae)

Gastrothylax crumenifer haemoglobin was isolated, purified, chromatographed, and its molecular weight determined on a calibrated Sephadex G–100 column as well as by sodium dodecyl sulphate by the former and 16 500 by the latter method. The oxygen affinity of the pigment (P50O2) was found to be 6·1 mm Hg at pH 7·4.

A comparative account of the tracheal system of larvae of the horse bot-fly,Gasterophilus intestinalis(De Geer), and of some other dipterous larvae

1. The tracheal systems of first, second and third instar larvae ofGasterophilus intestinalisare described.

2. The homologies of the conical tracheae of the tracheal organ are demonstrated and explain the apparent disappearance of a complete tracheal metamere.

3. Anomalies in the tracheal system of the anterior segments ofGasterophilusled to an investigation of the tracheal systems ofDrosophila, Eristalis, Calliphora, ScatopseandAëdes.

4. The anterior tracheal system of larval Diptera has been re-interpreted; that of the Cyclorrhapha can be derived from that of the Nematocera without the formation of new tracheae other than a large trachea from the lateral longitudinal trunk to the antero-lateral musculature.

David Keilin, 1887-1963

The sudden death on 27 February 1963 of David Keilin deprived the scientific world of a biologist the span of whose scientific activities is unlikely to be equalled, much less excelled, in the future. These activities extended from descriptive morphology of protists, fungi and insects to the biochemistry of respiratory enzymes and metallo-protein compounds. It is, consequently, not possible for one person to deal adequately with all aspects of his work and in this appreciation of the man and his scientific achievements the main emphasis will be on his biological work. That bearing on parasitology will be considered in some detail, whereas the later, more biochemical, work will be considered briefly as fuller accounts of it have already been given by E. F. Hartree (Biochem. J.89, 1–5), T. R. R. Mann (Biogr. Mem. Fellows R. Soc.10, 185–207) and E. C. Slater (Enzymologia, 26, 313–20). In the brief survey of his biochemical work I have made much use of summaries and reports written by Keilin himself and I have often given the essence of lines of work summed up in his own words which express his conclusions with the elegance, lucidity and brevity characteristic of his style. As I was closely associated with David Keilin and in almost daily contact with him for just on forty years, it is natural that the following account will to some extent reflect my own interests and those aspects of his personality which became manifested during long and intimate contact both in private life and collaboration in scientific and administrative work.

The respiratory proteins of insects

For a long time, respiratory proteins have been considered unnecessary in most insects because the tracheal system was thought to be sufficient for oxygen supply. Only a few species that survive under hypoxic conditions were known exceptions. However, recently it has become evident that (1) intracellular hemoglobins belong to the standard repertoire of insects and (2) that hemocyanin is present in many "lower" insects. Intracellular hemoglobins have been identified in Drosophila, Anopheles, Apis and many other insects. In all investigated species, hemoglobin is mainly expressed in the fat body and the tracheal system. The major Drosophila hemoglobin binds oxygen with high affinity. This hemoglobin type possibly functions as a buffer system for oxygen supply at low partial pressures and/or for the protection from an excess of oxygen. Similar hemoglobins, present in much higher concentrations, store oxygen in specialized tracheal organs of the botfly and some backswimmers. The extracellular hemoglobins in the hemolymph of chironomid midges are evolutionary derivatives of the intracellular insect hemoglobins, which emerged in response to the hypoxic environment of the larvae. In addition, several hemoglobin variants of unknown functions have been discovered in insect genomes. Hemocyanins transport oxygen in the hemolymph of stoneflies, but also in the Entognatha and most hemimetabolan taxa. Apparently, hemocyanin has been lost in Holometabola. At present, no physiological or morphological character is known that could explain the presence or loss of hemocyanins in distinct taxa. Nevertheless, the occurrence of respiratory proteins in insects adds further complexity to our view on insect respiration.

Characterization of two globin genes from the malaria mosquito Anopheles gambiae: divergent origin of nematoceran haemoglobins

The chironomid midges are the only insects that harbour true haemoglobin in their haemolymph. Here we report the identification of haemoglobin genes in two other nematoceran species. Two paralogous haemoglobin genes (glob1 and glob2) from the malaria mosquito Anopheles gambiae were cloned and sequenced. Furthermore, we identified two orthologous haemoglobin genes in the yellow fever mosquito Aedes aegypti. All four haemoglobins were predicted to be intracellular proteins, with the amino acids required for heme- and oxygen-binding being conserved. In situ-hybridization studies showed that glob1 and glob2 expression in An. gambiae is mainly associated with the tracheal system. This pattern resembles that of other insect intracellular globins. We also observed expression of glob2 in visceral muscles. Phylogenetic analyses showed that the globins of the mosquitoes and the Chironomidae are not orthologous. The chironomid haemoglobins share a recent common origin with the brachyceran glob1 proteins. The mosquito glob1 and glob2 proteins, which separated by gene duplication around 170 million years ago, form a distinct clade of more ancient evolutionary origin within the insects. The glob1 genes have introns in the ancestral globin positions B12.2 and G7.0. An additional intron was observed in Ae. aegypti glob1 helix position E18.0, providing evidence for a recent intron gain event. Both mosquito glob2 genes have lost the B12.2 intron. This pattern must be interpreted in terms of dynamic intron gain and loss events in the globin gene lineage.

The hemoglobin genes of Drosophila

We recently reported the unprecedented occurrence of a hemoglobin gene (glob1) in the fruitfly Drosophila melanogaster. Here we investigate the structure and evolution of the glob1 gene in other Drosophila species. We cloned and sequenced glob1 genes and cDNA from D. pseudoobscura and D. virilis, and identified the glob1 gene sequences of D. simulans, D. yakuba, D. erecta, D. ananassae, D. mojavensis and D. grimshawi in the databases. Gene structure (introns in helix positions D7.0 and G7.0), gene synteny and sequence of glob1 are highly conserved, with high ds/dn ratios indicating strong purifying selection. The data suggest an important role of the glob1 protein in Drosophila, which may be the control of oxygen flow from the tracheal system. Furthermore, we identified two additional globin genes (glob2 and glob3) in the Drosophilidae. Although the sequences are highly derived, the amino acids required for heme- and oxygen-binding are conserved. In contrast to other known insect globin, the glob2 and glob3 genes harbour both globin-typical introns at positions B12.2 and G7.0. Both genes are conserved in various drosophilid species, but only expression of glob2 could be demonstrated by western blotting and RT-PCR. Phylogenetic analyses show that the clade leading to glob2 and glob3, which are sistergroups, diverged first in the evolution of dipteran globins. glob1 is closely related to the intracellular hemoglobin of the botfly Gasterophilus intestinalis, and the extracellular hemoglobins from the chironomid midges derive from this clade.

Modulation of oxygen binding to insect hemoglobins: the structure of hemoglobin from the botfly Gasterophilus intestinalis

Hemoglobins (Hbs) reversibly bind gaseous diatomic ligands (e.g., O2) as the sixth heme axial ligand of the penta-coordinate deoxygenated form. Selected members of the Hb superfamily, however, display a functionally relevant hexa-coordinate heme Fe atom in their deoxygenated state. Endogenous heme hexa-coordination is generally provided in these Hbs by the E7 residue (often His), which thus modulates accessibility to the heme distal pocket and reactivity of the heme toward exogenous ligands. Such a pivotal role of the E7 residue is prominently shown by analysis of the functional and structural properties of insect Hbs. Here, we report the 2.6 A crystal structure of oxygenated Gasterophilus intestinalis Hb1, a Hb known to display a penta-coordinate heme in the deoxygenated form. The structure is analyzed in comparison with those of Drosophila melanogaster Hb, exhibiting a hexa-coordinate heme in its deoxygenated derivative, and of Chironomus thummi thummi HbIII, which displays a penta-coordinate heme in the deoxygenated form. Despite evident structural differences in the heme distal pockets, the distinct molecular mechanisms regulating O2 binding to the three insect Hbs result in similar O(2 affinities (P50 values ranging between 0.12 torr and 0.46 torr).

The hemoglobin of the sea lamprey, Petromyzon marinus

The blood hemoglobin of the sea lamprey presents a curious mixture of primitive and highly specialized properties. Like muscle hemoglobin, it has a molecular weight of about 17,000, and apparently contains a single heme. Its isoelectric point is like that of a typical invertebrate hemoglobin. Its amino acid composition is partly characteristic of invertebrate) partly of vertebrate hemoglobins (Pedersen; Roche and Fontaine). In the present experiments, the oxygen equilibrium curve of this pigment was measured at several pH's. As expected, it is a rectangular hyperbola, the first such function to be observed in a vertebrate blood hemoglobin. Other hemoglobins known to possess this type of oxygen dissociation curve-those of vertebrate muscle, the worm Nippostrongylus, and the bot-fly larva-appear to serve primarily the function of oxygen storage rather than transport. Lamprey hemoglobin on the contrary is an efficient oxygen-transporting agent. It achieves this status by having, unlike muscle hemoglobin, a relatively low oxygen affinity, and a very large Bohr effect. In these properties it rivals the most effective vertebrate blood hemoglobins.

Characterization of Drosophila hemoglobin. Evidence for hemoglobin-mediated respiration in insects

In contrast to previous assumptions, the fruit fly Drosophila melanogaster possesses hemoglobin. This respiratory protein forms a monomer of about 17 kDa that is not exported into the hemolymph. Recombinant Drosophila hemoglobin displays a typical hexacoordinated deoxy spectrum and binds oxygen with an affinity of 0.12 torr. Four different hemoglobin transcripts have been identified, which are generated by two distinct promoters of the hemoglobin (glob1) gene but are identical in their coding regions. Putative binding sites for hypoxia-regulated transcription factors have been identified in the gene. Hemoglobin synthesis in Drosophila is mainly associated with the tracheal system and the fat body. This suggests that oxygen supply in insects may be more complex than thought previously and may depend on hemoglobin-mediated oxygen transport and storage in addition to simple diffusion.

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.

Structural, functional, and genetic characterization of Gastrophilus hemoglobin

Hemoglobin of Gastrophilus intestinalis (Insecta, Diptera), was purified and characterized. At least two isoforms have been identified by isoelectrofocusing, mass spectrometry, and genomic Southern blotting. Functional studies show a high oxygen affinity due to a low ligand dissociation rate (koff = 2.4 s-1) and a relatively high autoxidation rate (t1/2 = 1.6/h). The globins were separated under denaturing conditions, and the sequence of Hb1 (Mr = 17,965 +/- 2) was determined at the protein and DNA level. The open reading frame codes for a polypeptide of 150 amino acids. Although the globin is distantly related to globins from other species, it has a low penalty score against globin templates. Freshly isolated hemoglobin was crystallized from polyethylene glycol. Crystals contain two hemoglobin molecules per asymmetric unit. Solution of the three-dimensional structure by molecular replacement could not be achieved, possibly due to the presence of three protein isoforms in the crystals. In order to determine its three-dimensional structure, G. intestinalis Hb1 was overexpressed in Escherichia coli, resulting in a fully functional molecule as confirmed by ligand binding affinity. The globin gene contains two introns at positions D7.0 and G7.0. The D7.0 intron is unprecedented, suggesting that globin gene evolution is much more complex than originally thought.

The secretion of oxygen into the swim-bladder offish. II. The simultaneous transport of carbon monoxide and oxygen

Toadfish, Opsanus tau, L., were maintained in sea water equilibrated with gas mixtures containing a fixed proportion of oxygen and varying proportions of carbon monoxide. The swim-bladder was emptied by puncture, and, after an interval of 24 or 48 hours, the newly secreted gases were withdrawn and analyzed. Both carbon monoxide and oxygen are accumulated in the swim-bladder at tensions greater than ambient. The ratio of concentrations, carbon monoxide (secreted): carbon monoxide (administered) bears a constant relation to the ratio, oxygen (secreted): oxygen (administered). The value of the partition coefficient describing this relation is (alpha = 5.44). The two gases are considered to compete for a common intracellular carrier mediating their active transport. The suggestion is advanced that the intracellular oxygen carrier is a hemoglobin. Comparison of the proportions of carboxy- and oxyhemoglobin in the blood with the composition of the secreted gas proves that the secreted gases are not evolved directly from combination with blood hemoglobin. The suggestion is advanced that cellular oxygen secretion occurs in the rete mirabile: the rete may build up large oxygen tensions in the gas gland capillaries. It is suggested that the gas gland acts as a valve impeding back diffusion of gases from the swim-bladder.

Participation of a non-respiratory ferrous complex during mitosis in roots

A systematic survey was undertaken, of the effects of carbon monoxide and hydrogen cyanide (in the presence of 20 per cent oxygen), in darkness and light, on the relative rates of respiration, mitosis, and interphase in pea root tips. The inhibition of respiration by carbon monoxide was light-sensitive, but the inhibition by hydrogen cyanide was light-stable. The inhibitions were presumably due to combination of the inhibitor with the iron of cytochrome oxidase, in its divalent and trivalent forms respectively. In contrast, the inhibitions of mitosis by both poisons proved to be light-sensitive. The light-sensitive inhibition of mitosis by carbon monoxide shows that an iron complex is responsible for the process. That the inhibition of mitosis by hydrogen cyanide is also light-reversible shows that, in contrast with cytochrome oxidase, the mitotic iron complex remains always in the divalent state. The relative affinities of the mitotic ferrous complex, in molar units, were 0.68 for CO/O₂, and 0.37 for HCN/O₂. The properties of the complex are analogous to, yet distinct from, Gastrophilus haemoglobin and reduced cytochrome oxidase. It is considered that the arrest of mitosis by oxygen lack, carbon monoxide, and hydrogen cyanide is definitely due to interference with this unidentified, non-respiratory ferrous complex.

Metabolism of haemoglobin and haematin compounds in Ascaris lumbricoides

Variations in the colour of individual Ascciris lumbricoides from the pig are shown to depend on changes in the concentration of the perienteric fluid haemoglobin. Whilst the concentra­tion of the haemoglobin remains constant for several days when the worms are kept in a saline solution, it is rapidly increased when suitable substrates are added to the medium. These must always include a porphyrin or metalloporphyrin containing a vinyl group. Horse haemoglobin was found to be the most suitable substrate under the experimental conditions. Simpler substances cannot be utilized for haemoglobin synthesis. This is only the second example of inability to synthesize protohaematin which is known in the Metazoa. The distribution of haematin has been studied in whole worms and in histological sections by means of peroxidatic reactions. Only the cuticle and the excretory canal appear to be haematin-free. The amount of haemoglobin in the body wall does not seem to fluctuate like that in the perienteric fluid. More is present in the hypodermal layers and the nerve ring than in the actual musculature. Haematin compounds occur in relatively large amounts in the reproductive system, and have been studied spectroscopically in suspensions of uterine eggs. Consideration of the known reactions of the perienteric fluid haemoglobin with oxygen lead to the conclusion that it cannot be effective as a storer or carrier of oxygen in the metabolism of the worm itself. It is suggested that it represents a metabolic pool of haematin from which other haemoproteins are elaborated, and that the variation in concentration is the result of a mechanism for allowing the worm to store haematin at times when it is present in excess in the gut of the host. It is further suggested that the primary function of this mechanism is to enable a maximal rate of egg laying to be maintained. The haematin content of the eggs and the numbers laid would readily account for the quantity of haemoglobin involved. Although the data are insufficient to enable any generalization to be made at present, there are indications that similar phenomena occur in other ascarids and more distantly related nematodes.

Naturally crystalline hemoglobin of the nematode Mermis nigrescens. An in situ microspectrophotometric study of chemical properties and dichroism

A dichroic microspectrophotometer was used to measure isotropic and dichroic absorbance spectra of this unique cytoplasmic hemoglobin and its derivatives. A perfusion slide enabled changing the media bathing the Mermis head. The native spectrum, which has an exceptionally low alpha-band extinction, was shown to be entirely due to oxyhemoglobin. The CO-hemoglobin spectrum is more typical, however, the alpha- and beta-bands are unusually closely spaced. A ferric hemochrome was formed on oxidation with ferricyanide or hydroxylamine and was readily converted to ferric hemoglobin cyanide on adding cyanide. Aquoferric hemoglobin and ferric hemoglobin fluoride were not easily formed. Deoxyhemoglobin, identified by its typical absorption spectrum, was formed only under the extremely low O2 pressures attainable in the presence of dithionite. A glucose oxidase, catalase solution deoxygenated hemoglobin in human erythrocytes but not in adjacent Mermis preparations. The affinity for O2 is much greater than for CO. Also, spectral evidence points to an oxyheme environment that is different than in vertebrate hemoglobin and myoglobin. The polarization ratio (PR) magnitude and the PR spectrum were unaffected by perfusion with high refractive index solvents; therefore, form dichroism due to the rodlike crystals is negligible. Maximum extinction is approximately perpendicular to the long axis of the microscopic crystals, which are oriented parallel to the body axis within the hypodermal cells. The PR spectra of the hemoglobin derivatives strongly resemble the corresponding spectra previously reported of single crystals made of horse hemoglobin, whale myoglobin, or Aplysia myoglobin and change appropriately when the ligand is changed. This confirms that the intracellular crystals of Mermis are of oxyhemoglobin.

Fat body: a site of hemoglobin synthesis in Chironomus thummi (diptera)

Fourth instar larvae of Chironomus thummi were permitted to incorporate labeled amino acids and/or sigma-aminolevulinic acid (sigma-ALA) in vivo and in organ culture. The products secreted into the hemolymph or into the culture medium were examined by acrylamide gel electrophoresis. Nine electrophoretic bands can be resolved as hemoglobins without staining. When gels are sliced for scintillation counting, incorporated amino acids and sigma-ALA are shown to be associated primarily with the same nine hemoglobin bands, suggesting that hemoglobins are assembled and secreted. Staining of gels with Coomassie brilliant blue reveals that there are several bands in addition to the visible hemoglobins. These bands incorporate amino acids, but not sigma-ALA, suggesting that they are non-heme proteins. The results of culturing isolated salivary glands, gut, and fat body demonstrate that the fat body is the major site of hemoglobin synthesis and secretion. Labeled products of the gut represent about 5% of the total hemoglobins produced by the tissues, while no hemoglobins are produced by the salivary glands. Although nine hemoglobins are visibly resolved on gels, labeling techniques reveal as many as 14 hemoglobins. This is the first demonstration of hemoglobin synthesis by specific tissues in culture in an invertebrate.

The kinetics of binding of oxygen and carbon monoxide to Gastrophilus haemoglobin

The dimeric haemoglobin in the tracheal cells of the Gastrophilus larva was extracted and purified, and the spectral properties of its oxy- and carbon monoxide adducts are recorded. In dilute solutions the kinetic parameters of binding of oxygen and carbon monoxide were determined. In solutions between 0.1 and 50mum for oxygen k(on) is 1x10(7)m(-1).s(-1) and k(off) is 1s(-1); for carbon monoxide l(on) is 6.5x10(5)m(-1).s(-1) and l(off) is 0.14s(-1). These values are in agreement with previous equilibrium results on oxygen binding and carbon monoxide/oxygen partition. These results are discussed and compared with the known values for other monomeric protohaem proteins.