Anatomy of the photodissociation region in the orion bar

Much of the interstellar gas resides in photodissociation regions whose chemistry and energy balance is controlled by the flux of far-ultraviolet radiation upon them. These photons can ionize and dissociate molecules and heat the gas through the photoelectric effect working on dust grains. These regions have been extensively modeled theoretically, but detailed observational studies are few. Mapping of the prominent Orion Bar photodissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(1) line of molecular hydrogen, and the J = 1-0 rotational line of carbon monoxide allows the penetration of the far-ultraviolet radiation into the cloud to be traced. The results strongly support the theoretical models and show conclusively that the incident far-ultraviolet radiation field, not shocks as has sometimes been proposed, is responsible for the emission in the Orion Bar.

Energy generation in parasitic helminths

Although parasitic helminths are a very heterogeneous group of organisms, they share many interesting properties in their energy metabolism. In certain stages of their life cycle, they all have a large capacity for anaerobic functioning. In other stages, an aerobic energy metabolism prevails. Parasites have to adapt to different environments in which the availability of oxygen and food varies widely. These variations in their external conditions strongly influence their energy metabolism. Here, Louis Tielens presents an introduction to the current ideas on the bioenergetics of parasitic helminths, focusing on the differences in energy metabolism between various stages (free-living and parasitic), and paying special attention to the mechanisms involved in the transitions between the different methods of energy generation.

Fasciola hepatica miracidia are dependent on respiration and endogenous glycogen degradation for their energy generation

It is generally accepted that free-living stages of parasitic helminths are dependent on aerobic degradation of endogenous energy sources for their energy generation. This concept, however, is not the result of extensive experimental evidence, but originated mainly intuitively as oxygen is widely available in their habitat and these stages generally have a small size. Schistosoma mansoni, the sole parasitic helminth whose energy metabolism has been studied throughout its life-cycle indeed has aerobically functioning free-living stages. However, large differences exist in energy metabolism between adult stages of distinct parasitic helminths, and caution should be taken in predicting that all free-living stages of all parasitic helminths have the same, aerobic energy metabolism. Hence, this report studied the energy metabolism of Fasciola hepatica miracidia and demonstrated that F. hepatica miracidia are also dependent on aerobic degradation of their endogenous glycogen stores by glycolysis and on Krebs cycle activity for energy generation. However, in contrast to S. mansoni, F. hepatica miracidia cannot function anaerobically, as inhibition of the respiratory chain blocked motility and carbohydrate degradation, and finally resulted in death of the miracidia. Therefore, this report demonstrated that differences exist between miracidia of distinct species, in pre-adaptation of their energy metabolism to the occasional hypoxic conditions within their next host.

R-O-C(triple bond)N species produced by ion irradiation of ice mixtures: comparison with astronomical observations

We have investigated the effects induced by ion bombardment of mixtures containing nitrogen-bearing compounds at low temperatures. The results show the formation of a band at 2080 cm-1 in binary mixtures, NH3:CH4 and N2:CH4, which we attribute to HCN embedded in the organic residue formed by ion irradiation. In addition to this band, ternary mixtures containing an oxygen-bearing species (i.e., H2O) form a compound with a prominent absorption band at about 2165 cm-1 (4.62 microns). We ascribe this band to a nitrile compound containing O that is bonded to the organic residue. A detailed comparison of the laboratory results with astronomical data of the 4.62 microns absorption band in protostellar spectra shows good agreement in peak position and profile. Our experimental studies show that N2, which is a more likely interstellar ice component than NH3, can be the molecular progenitor of the carrier of the interstellar band. This is an alternative to the pathway by which UV photolysis of NH3-containing ices produces the 4.62 microns band and implies that ion bombardment may well play an important role in the evolution of interstellar ices. Here, we discuss the implications of our studies for the chemical route by which the carrier of the 4.62 microns band is formed in these laboratory experiments.

Titanium carbide nanocrystals in circumstellar environments

Meteorites contain micrometer-sized graphite grains with embedded titanium carbide grains. Although isotopic analysis identifies asymptotic giant branch stars as the birth sites of these grains, there is no direct observational identification of these grains in astronomical sources. We report that infrared wavelength spectra of gas-phase titanium carbide nanocrystals derived in the laboratory show a prominent feature at a wavelength of 20.1 micrometers, which compares well to a similar feature in observed spectra of postasymptotic giant branch stars. It is concluded that titanium carbide forms during a short (approximately 100 years) phase of catastrophic mass loss (>0.001 solar masses per year) in dying, low-mass stars.

Recognition of schistosome glycolipids by immunoglobulin E: possible role in immunity

To investigate the role of antibody responses to (glyco)lipids in immunity to schistosome infection, lipids extracted from Schistosoma mansoni eggs and adult worms were fractionated, and the antibody isotype profile reactive to the fractionated lipids in a well-characterized S. haematobium-infected population was investigated. In tests of 10 plasma samples it was found that immunoglobulin G (IgG) reactivity was highest to the fraction containing ceramidepolyhexosides, whereas IgE reactivity was most prominent to both cerebroside- and ceramidepolyhexoside-containing fractions. The fraction containing ceramidepolyhexosides was then tested for reactivity with IgG subclasses and IgE in plasma samples from 66 S. haematobium-infected patients. Considering IgG4 and IgE, isotypes of particular interest in helminth infections, we found that both isotypes recognized egg (glyco)proteins in more than 90% of the infected subjects. However, in the case of glycolipids, IgE reactivity was much more prominent than IgG4 reactivity (found in 80 and 41% of the subjects, respectively). Furthermore, worm glycolipid-specific IgE prior to treatment of the subjects with praziquantel was negatively correlated with egg counts at 2 years posttreatment, indicating that IgE directed towards glycolipids could play an important role in resistance to reinfection.

Low-temperature crystallization of silicate dust in circumstellar disks

Silicate dust in the interstellar medium is observed to be amorphous, yet silicate dust in comets and interplanetary dust particles is sometimes partially crystalline. The dust in disks that are thought to be forming planets around some young stars also appears to be partially crystalline. These observations suggest that as the dust goes from the precursor clouds to a planetary system, it must undergo some processing, but the nature and extent of this processing remain unknown. Here we report observations of highly crystalline silicate dust in the disks surrounding binary red-giant stars. The dust was created in amorphous form in the outer atmospheres of the red giants, and therefore must be processed in the disks to become crystalline. The temperatures in these disks are too low for the grains to anneal; therefore, some low-temperature process must be responsible. As the physical properties of the disks around young stars and red giants are similar, our results suggest that low-temperature crystallization of silicate grains also can occur in protoplanetary systems.

Studies on phospholipid turnover argue against sloughing of tegumental membranes in adult Schistosoma mansoni

The tegumental membrane complex of Schistosoma mansoni is the site of interaction between the parasite and the host. The tegument is involved in uptake of many nutrients, but also plays a crucial role in the evasion of the actions of the host immune system. Essential for the success of this evasion is maintaining the integrity of the tegumental membranes. The rate of turnover of phospholipids was investigated by pulse-labelling worms cultured in vitro, followed by additional incubation in the presence of unlabelled substrates. Tegumental membranes were isolated, characterized using antibodies against specific tegumental proteins, and analysed. It was demonstrated that the most prominent fatty acid found in tegumental phospholipids, palmitate, incorporated rapidly into the phospholipid fraction during a 30 min pulse labelling. In a subsequent 20 h chase with unlabelled substrates, the incorporated radioactivity was lost again from the tegumental membrane complex. This high turnover of palmitate was found to be limited to phosphatidylcholine (PC) only. The turnover was due to deacylation/reacylation, and not to the sloughing of membranes as is the case in schistosomula. It is speculated that this rapid turnover of PC in the tegument of adult schistosomes plays a new and important role in the immune evasion by the parasite.

The interstellar 4.62 micron band

We present new 4.5-5.1 micron (2210-1970 cm-1) spectra of embedded protostars, W33 A, AFGL 961 E, AFGL 2136, NGC 7538 IRS 9, and Mon R2 IRS 2, which contain a broad absorption feature located near 4.62 micron (2165 cm-1), commonly referred to in the literature as the "X-C triple bond N" band. The observed peak positions and widths of the interstellar band agree to within 2.5 cm-1 and 5 cm-1, respectively. The strengths of the interstellar 4.62 micrometers band and the ice absorption features in these spectra are not correlated, which suggests a diversity of environmental conditions for the ices we are observing. We explore several possible carriers of the interstellar band and review possible production pathways through far-ultraviolet photolysis (FUV), ion bombardment of interstellar ice analog mixtures, and acid-base reactions. Good fits to the interstellar spectra are obtained with an organic residue produced through ion bombardment of nitrogen-containing ices or with the OCN- ion produced either through acid-base reactions or FUV photolysis of NH3-containing ices.

Rapid separation and identification of phosphatidylethanolamine molecular species

A novel high performance liquid chromatography method is presented for the separation and identification of intact molecular species of phosphatidylethanolamine (PE). After isocratic separation, detection of species can be achieved by measurement of UV absorbance as well as by the quantitative method of light scattering detection. A mathematical relationship exists between i) the relative retention time of a PE molecular species and ii) the number of carbon atoms and double bonds in the aliphatic groups of the species. This relationship can aid in the identification of the species. Furthermore, the absence of non-volatile components in the solvent allows the use of electrospray mass spectrometry to identify the eluting components and to establish the position of the individual radyl groups at the glycerol backbone. Using this method, samples of bovine heart PE (rich in plasmalogens) and rat liver PE (rich in diacyl species) have been analyzed.

Near-infrared spectroscopy of the proto-planetary nebula CRL 618 and the origin of the hydrocarbon dust component in the interstellar medium

A new 2.8-3.8 micrometers spectrum of the carbon-rich protoplanetary nebula CRL 618 confirms the previous detection of a circumstellar 3.4 micrometers absorption feature in this object (Lequeux & Jourdain de Muizon). The high resolution and high signal-to-noise ratio of our spectrum allow us to derive the detailed profile of this absorption feature, which is very similar to that observed in the spectrum of the Galactic center and also resembles the strong 3.4 micrometers emission feature in some post-asymptotic giant branch stars. A weak 3.3 micrometers unidentified infrared band, marginally detected in the CRL 618 spectrum of Lequeux & Jourdain de Muizon, is present in our spectrum. The existence of the 3.4 micrometers feature implies the presence of relatively short-chained, aliphatic hydrocarbon materials (-CH2-/-CH3 approximately = 2-2.5) in the circumstellar environment around CRL 618. It also implies that the carriers of the interstellar 3.4 micrometers feature are produced at least in part in circumstellar material, and it calls into question whether any are produced by the processing of interstellar ices in dense interstellar clouds, as has been previously proposed. Other features in the spectrum are recombination lines of hydrogen, rotational and vibration-rotation lines of molecular hydrogen, and a broad absorption probably due to a blend of HCN and C2H2 bands.

Ether lipids and their possible physiological function in adult Schistosoma mansoni

Schistosomes have lost the capability to synthesize fatty acids de novo, but they can modify fatty acids by chain elongation. This has a profound effect on the molecular species composition of the two main phospholipid fractions of schistosomes, phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Molecular species of phospholipids are increasingly recognized as important mediators, or precursors thereof, in signal transduction, immune response modulation, and events like membrane fusion. As these are all important aspects of schistosome membranes and of the tegumental membranes in particular, we analysed the PE and PC molecular species of the tegumental membranes, the worm body and the blood of the host. With the aid of on-line mass spectrometry, we unequivocally identified a large number of PC and PE species in schistosomes, among which considerable amounts of plasmalogen species. This was unexpected, as this lipid subclass has been assumed to be absent in the parasite. Species, like (20:1-16:0) diacyl PC and (16:0-20:1) plasmalogen PE, found to be main constituents in schistosomes, were absent from the blood of the host. Large differences were also found between the molecular species composition of the tegumental membranes and the membranes of the worm body. In the tegumental membranes, 1-hexadecyl 2-palmitoyl PC was detected, which could possibly function as a precursor for platelet activating factor (PAF).

Glucose Transport and Metabolism in Mammalian-stage Schistosomes

Adult schistosomes transport nutrients from the host bloodstream across their outer body covering or tegument. The tegument is a cytologically unusual structure; it is a syncytium bounded externally by two lipid bilayer membranes. In this review, Patrick Skelly, Louis Tielens and Chuck Shoemaker reconsider our understanding of how glucose enters schistosomes across this unusual outer covering in the light of recent papers characterizing glucose transport proteins and glucose metabolism pathways in these parasites.

5-Octadecenoic acid: evidence for a novel type of fatty acid modification in schistosomes

The lipid metabolism of schistosomes is characterized by several intriguing adaptations to a parasitic way of living. The surface of the parasite consists of two closely apposed phospholipid bilayers, a structure unique to blood flukes. Schistosomes do not synthesize fatty acids de novo, but are able to modify fatty acids, which they obtain from the host, by chain elongation. Here we present evidence that schistosomes are capable of another type of fatty acid modification, resulting in the formation of 5-octadecenoic acid [C18:1(5)]. This highly unusual fatty acid, which is absent in the blood of the host, was shown to be almost exclusively located in the outer membrane complex of the schistosome. Within these membranes, it was almost exclusively present in one molecular phospholipid species, 1-palmitoyl-2,5-octadecenoyl phosphatidylcholine [C16:0-18:1(5)PtdCho]. Apart from dipalmitoyl phosphatidylcholine, this was the most abundant phosphatidylcholine species in the outer membrane complex. The specific synthesis by the schistosome of C18:1(5) and the highly specific localization of this fatty acid to the tegumental membranes suggest an important tegument-mediated role for this lipid.

A gene encoding the plant-like alternative oxidase is present in Phytomonas but absent in Leishmania spp

The constituents of the respiratory chain are believed to differ among the trypanosomatids; bloodstream stages of African trypanosomes and Phytomonas promastigotes oxidize ubiquinol by a ubiquinol:oxygen oxidoreductase, also known as alternative oxidase, whereas Leishmania spp. oxidize ubiquinol via a classic cytochrome-containing respiratory chain. The molecular basis for this elementary difference in ubiquinol oxidation by the mitochondrial electron-transport chain in distinct trypanosomatids was investigated. The presence of a gene encoding the plant-like alternative oxidase could be demonstrated in Phytomonas and Trypanosoma brucei, trypanosomatids that are known to contain alternative oxidase activity. Our results further demonstrated that Leishmania spp. lack a gene encoding the plant-like alternative oxidase, and therefore, all stages of Leishmania spp. will lack the alternative oxidase protein. The observed fundamental differences between the respiratory chains of distinct members of the trypanosomatid family are thus caused by the presence or absence of a gene encoding the plant-like alternative oxidase.

Differences in Energy Metabolism Between Trypanosomatidae

Although various members of the family Trypanosomatidae generate energy in a similar way, fundamental differences also exist and are not always recognized. In this review, Louis Tielens and Jaap Van Hellemond discuss the known differences in carbohydrate metabolism among trypanosomatids, and especially compare Leishmania with trypanosomatids such as Trypanosoma brucei and Phytomonas spp. Special attention will be paid to differences in end-products of carbohydrate degradation, to differences in anaerobic capacities between the various trypanosomatids and to the components of their respiratory chains, including the presence or absence of a plant-like alternative oxidase. Furthermore, evidence will be discussed which indicates that the succinate produced by trypanosomatids is formed mainly via an oxidative pathway and not via reduction of fumarate, a process known to occur in parasitic helminths.

The electron transport chain in anaerobically functioning eukaryotes

Many lower eukaryotes can survive anaerobic conditions via a fermentation pathway that involves the use of the reduction of endogenously produced fumarate as electron sink. This fumarate reduction is linked to electron transport in an especially adapted, anaerobically functioning electron-transport chain. An aerobic energy metabolism with Krebs cycle activity is accompanied by electron transfer from succinate to ubiquinone via complex II of the respiratory chain. On the other hand, in an anaerobic metabolism, where fumarate functions as terminal electron acceptor, electrons are transferred from rhodoquinone to fumarate, which is the reversed direction. Ubiquinone cannot replace rhodoquinone in the process of fumarate reduction in vivo, as ubiquinone can only accept electrons from complex II and cannot donate them to fumarate. Rhodoquinone, with its lower redox potential than ubiquinone, is capable of donating electrons to fumarate. Eukaryotic fumarate reductases were shown to interact with rhodoquinone (a benzoquinone), whereas most prokaryotic fumarate reductases interact with the naphtoquinones menaquinone and demethylmenaquinone. Fumarate reductase, the enzyme essential for the anaerobic functioning of many eukaryotes, is structurally very similar to succinate dehydrogenase, the Krebs cycle enzyme catalysing the reverse reaction. In prokaryotes these enzymes are differentially expressed depending on the external conditions. Evidence is now emerging that also in eukaryotes two different enzymes exist for succinate oxidation and fumarate reduction that are differentially expressed.

Processing of icy mantles in protostellar envelopes

We have obtained CO absorption profiles of several young stellar objects (YSOs), spanning a range of mass and luminosity, in order to investigate their ice mantle composition. We present the first detection of CO toward the class I YSO L1489 IRS in the Taurus dark cloud. In general, the CO profiles for YSOs show evidence for both processed and pristine ices in the same line of sight, strong indirect evidence for CO, is suggested in R CrA IRS 7, L1489 IRS, Elias 18, and GL 961E. Toward other sources (R CrA IRS 1, IRS 2, W33A, NGC 7538 IRS 9, Mon R2 IRS 2) CO is present in (nearly) pure form. We propose an evolutionary scenario to explain the chemical diversity of the icy mantles toward these objects.

Trypanosomatidae produce acetate via a mitochondrial acetate:succinate CoA transferase

Hydrogenosome-containing anaerobic protists, such as the trichomonads, produce large amounts of acetate by an acetate:succinate CoA transferase (ASCT)/succinyl CoA synthetase cycle. The notion that mitochondria and hydrogenosomes may have originated from the same alpha-proteobacterial endosymbiont has led us to look for the presence of a similar metabolic pathway in trypanosomatids because these are the earliest-branching mitochondriate eukaryotes and because they also are known to produce acetate. The mechanism of acetate production in these organisms, however, has remained unknown. Four different members of the trypanosomatid family: promastigotes of Leishmania mexicana mexicana, L. infantum and Phytomonas sp., and procyclics of Trypanosoma brucei were analyzed as well as the parasitic helminth Fasciola hepatica. They all use a mitochondrial ASCT for the production of acetate from acetyl CoA. The succinyl CoA that is produced during acetate formation by ASCT is recycled presumably to succinate by a mitochondrial succinyl CoA synthetase, concomitantly producing ATP from ADP. The ASCT of L. mexicana mexicana promastigotes was further characterized after partial purification of the enzyme. It has a high affinity for acetyl CoA (Km 0.26 mM) and a low affinity for succinate (Km 6.9 mM), which shows that significant acetate production can occur only when high mitochondrial succinate concentrations prevail. This study identifies a metabolic pathway common to mitochondria and hydrogenosomes, which strongly supports a common origin for these two organelles.

Quantitative analysis of phosphatidylcholine molecular species using HPLC and light scattering detection

A number of HPLC chromatographic procedures can be used to separate intact molecular species of phosphatidylcholine (PC), but on-line quantification has remained problematic due to insensitivity of UV-detection for saturated species. Here, a new method is presented, separating all major PC molecular species from a variety of biological samples in intact form using a single, short and isocratic run. Species were separated on two RP18 reverse-phase columns in series and all species displayed an exponential relation between retention time and the percentage of acetonitrile or triethylamine in the mobile phase, allowing optimization of the mobile phase on a theoretical base, rather than on time-consuming test-runs. The use of triethylamine as a volatile additive instead of choline chloride allowed the use of light scattering detection. On a molar base, the response of the detector was invariant between species and allowed quantification of as little as 50 pmoles. The method was tested using phosphatidylcholines with widely different molecular species patterns, such a PC from rat liver, porcine pulmonary surfactant, bovine heart, boar sperm cells, and the parasite Schistosoma mansoni. As only volatile components are present in the solvents, individual molecular species can easily be recovered in pure form from the column effluent, enabling their further analysis (e.g., scintillation counting).

The incorporation, modification and turnover of fatty acids in adult Schistosoma mansoni

Schistosoma mansoni is known to be unable to synthesize fatty acids and sterols de novo, but the parasite is capable of synthesizing phospholipids and triacylglycerols from precursors obtained from the host. The present study focuses on the dynamics of the incorporation of fatty acids in adult parasites. This study showed that fatty acids were rapidly metabolized into complex lipids and that oleate (18:1) was efficiently converted to eicosenoate (20:1) by chain elongation, whereas palmitate was not elongated at an appreciable rate. This chain elongation mainly involved fatty acids that were previously esterified to complex lipids. Furthermore it was shown that in adult parasites triacylglycerols do not serve as fatty-acyl donors in phospholipid synthesis as had been suggested to be the case in schistosomula, because: (1) Immediately after pulse-labelling the specific activity of fatty acids in phospholipids was higher than in triacylglycerols; and (2) the specific activity of eicosenoate, which had been formed by chain elongation of incorporated oleate. was higher in phospholipids than in triacylglycerols. Fatty acids that were esterified to phospholipids had a high turnover, in contrast to fatty acids esterified to triacylglycerols, which persisted for extended periods of time in this lipid class (days rather than hours).

Schistosoma mansoni sporocysts contain rhodoquinone and produce succinate by fumarate reduction

Although schistosomes were thought to be one of the few parasitic helminths that do not produce succinate via fumarate reduction, it was recently demonstrated that sporocysts of Schistosoma mansoni produce, under certain conditions, succinate in addition to lactate. This succinate production was only observed when the respiratory chain activity of the sporocysts was inhibited, which suggested that succinate is produced by fumarate reduction. In this report the presence of essential components for fumarate reduction was investigated in various stages of S. mansoni and it was shown that, in contrast to adults, sporocysts contained a substantial amount of rhodoquinone which is essential for efficient fumarate reduction in eukaryotes. This rhodoquinone was not made by modification of ubiquinone obtained from the host, but was synthesized de novo. Furthermore, it was shown that complex II of the electron-transport chain in schistosomes has the kinetic properties of a dedicated fumarate reductase instead of those of a succinate dehydrogenase. The presence of such an enzyme, together with the substantial amounts of rhodoquinone, shows that in S. mansoni sporocysts succinate is produced via fumarate reduction. Therefore, the energy metabolism of schistosomes does not differ in principle from most other parasitic helminths, which are known to rely heavily on fumarate reduction.

Circumstellar and interstellar synthesis of organic molecules

We review the formation and evolution of complex circumstellar and interstellar molecules. A number of promising chemical routes are discussed which may lead to the formation of polycyclic aromatic hydrocarbon molecules, fullerenes, and unsaturated hydrocarbon chains in the outflows from stars. Some of the problems with these chemical schemes are pointed out as well. We also review the role of grains in the formation of complex molecules in interstellar molecular clouds. This starts with the formation of simple molecules in an ice grain mantle. UV photolysis and/or thermal polymerization can convert some of these simple molecules into more complex polymeric structures. Some of these species may be released to the gas phase, particularly in the warm regions around newly formed stars. Methanol and formaldehyde seem to play an important role in this drive towards molecular complexity and their chemistry is traced in some detail.

Rhodoquinone is synthesized de novo by Fasciola hepatica

Most adult parasitic helminths have an anaerobic energy metabolism in which fumarate is reduced to succinate by fumarate reductase. Rhodoquinone (RQ) is an essential component of the electron transport associated with this fumarate reduction, whereas ubiquinone (UQ) is used in the aerobic energy metabolism of parasites. Not known yet, however, is the RQ and UQ composition during the entire life cycle nor the origin of RQ in parasitic helminths. This report demonstrates the essential function of RQ in anaerobic energy metabolism during the entire life cycle of Fasciola hepatica, as the amount of RQ present reflected the importance of fumarate reduction in various stages. We also studied the origin of RQ, as earlier studies on the protozoan Euglena gracilis suggested that RQ is synthesized from UQ. Therefore, in parasitic helminths RQ might be synthesized by modification of UQ obtained from the host. However, we demonstrated that in F. hepatica adults RQ was not produced by modification of UQ obtained from the host but that RQ was synthesized de novo, as (i) the chain-length of the quinones of F. hepatica adults was not related to the chain length of the quinone of the host, (ii) despite many attempts we could never detect any in vitro conversion of UQ9 into RQ9 or into UQ10, neither by intact adult flukes nor by homogenates of F. hepatica adults and (iii) F. hepatica adults used mevalonate as precursor for the synthesis of RQ. We also showed that the rate of quinone synthesis in F. hepatica adults was comparable to that in the free-living nematode Caenorhabditis elegans. These results prompted the suggestion that RQ is synthesized via a pathway nearly identical to that of UQ biosynthesis: possibly only the last reaction differs.

The infrared spectrum of the Galactic center and the composition of interstellar dust

We have obtained 5-8 micrometers spectra of the Galactic center from the Kuiper Airborne Observatory at resolving powers of approximately 50, approximately 150, and approximately 300. These spectra show absorption features at 5.5, 5.8, 6.1, and 6.8 micrometers. Together with previously observed features in the 3 micrometers region, these features are compared with laboratory spectra of candidate materials. The 3.0 and 6.1 micrometers features are due to the OH stretching and bending variations of H2O and are well fitted by water of hydration in silicates (e.g., talc). The 3.0 micrometer band is equally well fitted by ice mixtures containing 30% H2O, but such mixtures do not provide a good fit to the observed 6.1 micrometer band. The 3.4 and 6.8 micrometers features are identified with the CH stretching and deformation modes in CH2 and CH3 groups in saturated aliphatic hydrocarbons. The 6.1 micrometer band shows a short wavelength shoulder centered on 5.8 micrometer, attributed to carbonyl (C double bond O) groups in this interstellar hydrocarbon dust component. Finally, the narrow 5.5 micrometer feature is also attributed to carbonyl groups, but in the form of metal carbonyls [e.g., Fe(CO)4]. We have derived column densities and abundances along the line of sight toward the Galactic center for the various identified dust components. This analysis shows that hydrocarbon grains contain only 0.08 of the elemental abundance of C and contribute only a relatively minor fraction (0.1) of the total dust volume. Most of the interstellar dust volume is made up of silicates (approximately 0.6). Small graphite grains, responsible for the 2200 angstroms bump, account for 0.07 of the total dust volume. The remaining one-quarter of the interstellar dust volume consists of a material(s) without strong IR absorption features. Likely candidates include large graphite grains, diamonds, or amorphous carbon grains, which all have weak or no IR active modes. Finally, various models for the origin of the hydrocarbon dust component of the interstellar dust are discussed. All of them face some problems in explaining the observations, in particular, the absence of the spectroscopic signature of hydrocrbon grains in sources associated with molecular clouds.

Spatial variation of the 3.29 and 3.40 micron emission bands within reflection nebulae and the photochemical evolution of methylated polycyclic aromatic hydrocarbons

Spectra of 3 micrometers emission features have been obtained at several positions within the reflection nebulae NGC 1333 SVS3 and NGC 2023. Strong variations of the relative intensities of the 3.29 micrometers feature and its most prominent satellite band at 3.40 micrometers are found. It is shown that (i) the 3.40 micrometers band is too intense with respect to the 3.29 micrometers band at certain positions to arise from hot band emission alone, (ii) the 3.40 micrometers band can be reasonably well matched by new laboratory spectra of gas-phase polycyclic aromatic hydrocarbons (PAHs) with alkyl (-CH3) side groups, and (iii) the variations in the 3.40 micrometers to 3.29 micrometers band intensity ratios are consistent with the photochemical erosion of alkylated PAHs. We conclude that the 3.40 micrometers emission feature is attributable to -CH3 side groups on PAH molecules. We predict a value of 0.5 for the peak intensity ratio of the 3.40 and 3.29 micrometers emission bands from free PAHs in the diffuse interstellar medium, which would correspond to a proportion of one methyl group for four peripheral hydrogens. We also compare the 3 micrometers spectrum of the proto-planetary nebula IRAS 05341+0852 with the spectrum of the planetary nebula IRAS 21282+5050. We suggest that a photochemical evolution of the initial aliphatic and aromatic hydrocarbon mixture formed in the outflow is responsible for the changes observed in the 3 micrometers emission spectra of these objects.

Assessment of the polycyclic aromatic hydrocarbon-diffuse interstellar band proposal

The potential link between neutral and/or ionized polycyclic aromatic hydrocarbons (PAHs) and the diffuse interstellar band (DIB) carriers is examined. Based on the study of the general physical and chemical properties of PAHs, an assessment is made of their possible contribution to the DIB carriers. It is found that, under the conditions reigning in the diffuse interstellar medium, PAHs can be present in the form of neutral molecules as well as positive and/or negative ions. The charge distribution of small PAHs is dominated, however, by two charge states at one time with compact PAHs present only in the neutral and cationic forms. Each PAH has a distinct spectral signature depending on its charge state. Moreover, the spectra of ionized PAHs are always clearly dominated by a single band in the DIB spectral range. In the case of compact PAH ions, the strongest absorption band is of type A (i.e., the band is broad, falls in the high-energy range of the spectrum, and possesses a large oscillator strength), and seems to correlate with strong and broad DIBs. For noncompact PAH ions, the strongest absorption band is of type I (i.e., the band is narrow, falls in the low-energy range of the spectrum, and possesses a small oscillator strength), and seems to correlate with weak and narrow DIBs. Potential molecular size and structure constraints for interstellar PAHs are derived by comparing known DIB characteristics to the spectroscopic properties of PAHs. It is found that (i) only neutral PAHs larger than about 30 carbon atoms could, if present, contribute to the DIBs. (ii) For compact PAHs, only ions with less than about 250 carbon atoms could, if present, contribute to the DIBs. (iii) The observed distribution of the DIBs between strong/moderate and broad bands on the one hand and weak and narow bands on the other can easily be interpreted in the context of the PAH proposal by a distribution of compact and noncompact PAH ions, respectively. A plausible correlation between PAH charge states and DIB "families" is thus provided by the PAH-DIB proposal. Following this proposal, DIB families would reflect conditions within a cloud which locally determine the relative importance of cations, anions, and neutral species, rather than tracers of a specific species. Observational predictions are given to establish the viability of the PAH hypothesis. It is concluded that small PAH ions are very promising candidates as DIB carriers provided their population is dominated by a finite number (100-200) of species. A key test for the PAH proposal, consisting of laboratory and astronomical investigations in the ultraviolet range, is called for.

Rhodoquinone and complex II of the electron transport chain in anaerobically functioning eukaryotes

Many anaerobically functioning eukaryotes have an anaerobic energy metabolism in which fumarate is reduced to succinate. This reduction of fumarate is the opposite reaction to succinate oxidation catalyzed by succinate-ubiquinone oxidoreductase, complex II of the aerobic respiratory chain. Prokaryotes are known to contain two distinct enzyme complexes and distinct quinones, menaquinone and ubiquinone (Q), for the reduction of fumarate and the oxidation of succinate, respectively. Parasitic helminths are also known to contain two different quinones, Q and rhodoquinone (RQ). This report demonstrates that RQ was present in all examined eukaryotes that reduce fumarate during anoxia, not only in parasitic helminths, but also in freshwater snails, mussels, lugworms, and oysters. It was shown that the measured RQ/Q ratio correlated with the importance of fumarate reduction in vivo. This is the first demonstration of the role of RQ in eukaryotes, other than parasitic helminths. Furthermore, throughout the development of the liver fluke Fasciola hepatica, a strong correlation was found between the quinone composition and the type of metabolism: the amount of Q was correlated with the use of the aerobic respiratory chain, and the amount of RQ with the use of fumarate reduction. It can be concluded that RQ is an essential component for fumarate reduction in eukaryotes, in contrast to prokaryotes, which use menaquinone in this process. Analyses of enzyme kinetics, as well as the known differences in primary structures of prokaryotic and eukaryotic complexes that reduce fumarate, support the idea that fumarate-reducing eukaryotes possess an enzyme complex for the reduction of fumarate, structurally related to the succinate dehydrogenase-type complex II, but with the functional characteristics of the prokaryotic fumarate reductases.

Schistosoma mansoni hexokinase: cDNA cloning and immunogenicity studies

DNA encoding a Schistosoma mansoni hexokinase (SHEX) was amplified from cDNA by the polymerase chain reaction using opposing oligonucleotide primers designed to hybridize with two short segments of hexokinase coding sequences that are well-conserved through evolution. The resulting DNA fragment was then used as a probe to identify a full-length hexokinase cDNA clone. SHEX cDNA encodes a 50-kDa protein that is approximately 46% homologous to rat hexokinase, 40% to rat glucokinase, and 34% to yeast hexokinase A. SHEX coding DNA was expressed within Escherichia coli cells and the 50-kDa recombinant product (rSHEX) was partially purified. Mice repeatedly immunized with rSHEX produced antibodies which recognize rSHEX but this offered no significant protection against subsequent cercarial challenge. On Western blots, rSHEX is weakly recognized by antisera against rat brain hexokinase but not by sera from three strains of mice experimentally infected with S. mansoni parasites or from numerous human schistosomiasis patients. Thus, unlike other reported S. mansoni glycolytic enzymes, hexokinase appears to be poorly immunogenic during schistosome infection and of limited potential as a vaccine candidate.

Expression and functional properties of fumarate reductase

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The 50-kDa glucose 6-phosphate-sensitive hexokinase of Schistosoma mansoni

Hexokinase has been purified from adult Schistosoma mansoni worms and the activity shown to be associated with a single protein species having an M(r) about 50,000. This protein is recognized on Western blots probed with antisera against rat Type I hexokinase or against a recombinant S. mansoni hexokinase that had been expressed in Escherichia coli using a previously cloned cDNA. An 18-residue N-terminal sequence determined for the purified S. mansoni hexokinase is identical to that deduced from the nucleotide sequence of the cDNA, consistent with the view that the cloned cDNA encodes the hexokinase characterized in the present study. The S. mansoni enzyme has a relatively low Km (approximately 60 microM) for glucose and is sensitive to inhibition (competitive versus ATP, Ki approximately 50 microM) by its product, glucose 6-phosphate (Glc-6-P). With these kinetic properties and 50 kDa molecular mass, S. mansoni hexokinase resembles the ancestral hexokinase predicted to have given rise, by gene duplication and fusion, to the present day 100-kDa Glc-6-P-sensitive mammalian hexokinases. The schistosomal hexokinase represents the first 50-kDa Glc-6-P-sensitive hexokinase whose sequence has been obtained. The schistosomal hexokinase does not bind to mitochondria, consistent with its lack of a hydrophobic segment at the N terminus which is required for binding of the mammalian Type I and II isoenzymes to mitochondria. The marked Crabtree effect exhibited by S. mansoni cercariae may be at least partly attributed to the expression of rather high levels of a hexokinase having a high affinity for glucose but only a moderate sensitivity to product inhibition by Glc-6-P.

Differential expression of two succinate dehydrogenase subunit-B genes and a transition in energy metabolism during the development of the parasitic nematode Haemonchus contortus

The carbohydrate metabolism of free-living and parasitic stages of the sheep nematode Haemonchus contortus was studied, and it was demonstrated that during development a switch occurred from Krebs-cycle activity towards a more fermentative metabolism. During this switch a transition might take place in complex II of the respiratory chain. In the free-living (L3) and early parasitic (XL3) stages, complex II catalyses the oxidation of succinate to fumarate via the Krebs cycle, whereas in adults complex II functions in the reverse reaction, the reduction of fumarate to succinate. L3 and XL3 were shown to already possess a large anaerobic capacity. They survived well in the absence of oxygen or in the presence of cyanide, which completely blocked respiration. Krebs-cycle activity, however, was only partially inhibited by cyanide; the XL3s in particular produced in the presence of cyanide large amounts of propanol, the production of which probably functions as an alternative electron sink. For further investigation of the observed metabolic switch, complex II of the respiratory chain, a key enzyme involved in this switch, was studied. The B subunit of complex II was cloned and sequenced. These clones all showed sequences similar to the B subunit of succinate dehydrogenase from other species, and included the amino-terminal signal sequence for importation into mitochondria. Two genes were identified, types 1 and 2, based on the DNA and amino acid sequences and on the lack of cross-reaction to each other when used as probes on Southern blots. On Northern blots, the two genes showed a different expression pattern during the development of the parasite.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic benfluorex treatment on the activities of key enzymes of hepatic carbohydrate metabolism in old Sprague-Dawley rats

Chronic effects of benfluorex on some parameters of carbohydrate metabolism have been studied in 24-month-old Sprague-Dawley rats. Treatment once a day for 14 days with 25 mg benfluorex per kg body weight lowered body weight, decreased circulating insulin and resulted in an increase in hepatic glycogen. Measurement of the activities of several important regulatory enzymes of hepatic carbohydrate metabolism showed a significant decrease in the activities of phosphoenolpyruvate carboxykinase and glycogen phosphorylase. The activity of glucose-6-phosphatase, on the other hand, was slightly increased. Taken collectively, our data offer an explanation for the observed inhibition of hepatic glucose production by chronic benfluorex treatment in cases of hyperinsulinemia.

Mid- and far-infrared spectroscopy of ices: optical constants and integrated absorbances

Laboratory spectra through the mid-infrared (4000 to 500 cm-1 [2.5-20 micrometers]) have been used to calculate the optical constants (n and k) and integrated absorption coefficients (A) for a variety of pure and mixed molecular ices of relevance to astrophysics. The ices studied were H2O, CH3OH, CO2, OCS, CH4, CO2 + CH4, CO2 + OCS, CO + CH4, CO + OCS, O2 + CH4, O2 + OCS, N2 + CH4, N2 + OCS, H2O + CH4, H2O + OCS, and H2O + CH3OH + CO + NH3. In addition, the measurements have been extended through the far-infrared (500 to 50 cm-1 [20-200 micrometers]) for the H2O, CH3OH, and H2O + CH3OH + CO + NH3 ices.

Diamonds in dense molecular clouds: a challenge to the standard interstellar medium paradigm

Observations of a newly discovered infrared C-H stretching band indicate that interstellar diamond-like material appears to be characteristic of dense clouds. In sharp contrast, the spectral signature of dust in the diffuse interstellar medium is dominated by -CH2- and -CH3 groups. This dichotomy in the aliphatic organic component between the dense and diffuse media challenges standard assumptions about the processes occurring in, and interactions between, these two media. The ubiquity of this interstellar diamond-like material rules out models for meteoritic diamond formation in unusual circumstellar environments and implies that the formation of the diamond-like material is associated with common interstellar processes or stellar types.

The facultative anaerobic energy metabolism of Schistosoma mansoni sporocysts

Schistosoma mansoni miracidia in water are known to possess an aerobic energy metabolism, the Krebs cycle being the main terminal of the breakdown of endogenous glycogen reserves. The present study demonstrated that after in vitro transformation of miracidia into sporocysts, the organisms degraded glucose to lactate and carbon dioxide in a more anaerobic ratio than do miracidia. The occurrence of a large Pasteur effect demonstrated, however, that oxidative phosphorylation was still the major process used for energy generation. After 24 h in vitro cultivation the sporocysts had consumed more external glucose and their metabolism had shifted towards lactate production. Sporocysts could cope with inhibited respiration: they had a large anaerobic capacity and survived perfectly in the presence of cyanide, producing a large amount of succinate in addition to lactate. It was demonstrated that this succinate was largely produced via phosphoenolpyruvate carboxykinase (PEPCK). This pathway, which is known to occur in most parasitic helminths, has never been demonstrated in schistosomes, not even in the miracidial stage immediately preceding the sporocysts. It was also shown that in sporocysts part of the lactate was not formed directly by glycolysis, but via a detour including fumarate and the action of PEPCK. The results demonstrated that S. mansoni sporocysts are facultative anaerobes, fully equipped to adjust their energy metabolism to the variable conditions inside their intermediate host, the snail. In the presence of oxygen, they derive most of their energy from the aerobic degradation of glucose to carbon dioxide, but under anaerobic conditions they switch towards lactate and succinate production.

Infrared spectroscopy of dense clouds in the C-H stretch region: methanol and "diamonds."

High spectral resolution (nu/delta nu = 900) studies in the 3100-2600 cm-1 (3.2-3.9 microns) range are presented of the protostars NGC 7538 IRS 9, W33A, W3 IRS 5, and S140 IRS 1. This is the spectral region in which the fundamental C-H stretching vibrations of aliphatic hydrocarbons fall. Well-resolved absorption bands at about 2825 cm-1 (3.54 microns) and 2880 cm-1 (3.47 microns) were found superposed on the low-frequency wing of the strong O-H stretch feature. The 2880 cm-1 (3.47 microns) band, a new interstellar feature, is moderately strong in the spectra of all four objects studied. The 2825 cm-1 (3.54 microns) band, previously detected toward W33A, is also in the spectrum of NGC 7538 IRS 9. The relative strength of these two bands varies, showing that they are associated with two different carriers. On the basis of comparisons with laboratory spectra, the 2825 cm-1 (3.54 microns) band is assigned to methanol (CH3OH), in agreement with the earlier work of Grim et al. (1991). This assignment is further supported by a pair of weak absorptions centered at 2600 and 2540 cm-1 (3.85 and 3.94 microns) in the spectrum of W33A recently reported by Geballe (1991). These features compare very well with laboratory spectra of CH3OH/H2O ice mixtures. The CH3OH/H2O ratio derived from the 2825 cm-1 methanol band and the 3250 cm-1 (3.08 microns) H2O feature are 0.13 and 0.40 for NGC 7538 IRS 9 and W33A, respectively. These values are smaller than the ratios of 0.61 and 0.54 derived using the 1460 cm-1 (6.85 microns) band assigned to CH3OH and the 1665 cm-1 (6.00 microns) H2O band. These apparent discrepancies may be due to a combination of scattering effects within the molecular cloud, uncertainties associated with the baselines for the 2825 cm-1 feature, and the presence of other interstellar grain materials that absorb at 1460 cm-1 (6.85 microns). Nonetheless, after H2O, CH3OH is the most abundant known interstellar ice constituent. The new band at about 2880 cm-1 (3.47 microns) falls near the position for C-H stretching vibrations in tertiary carbon atoms. The strength of this feature, in combination with the lack of strong features associated with primary (-CH3) and secondary (-CH2-) carbon atoms, suggests that the carrier of the new feature has a diamond-like structure. We therefore tentatively attribute this new feature to interstellar "diamonds." The detection of this band in the spectra of all four dense molecular clouds suggests that the carrier is ubiquitous in dense clouds. Band-strength analysis indicates that a minimum of a few percent of the available cosmic carbon is tied up in this material.

The reversible effect of glucose on the energy metabolism of Schistosoma mansoni cercariae and schistosomula

This study on isolated cercarial bodies demonstrates that the biological transformation from cercaria to schistosomulum and the biochemical transition from an aerobic to an anaerobic energy metabolism are separate processes, which are not necessarily linked. The metabolic transition depends on the external glucose concentration and is fully reversible. In the presence of only a tracer amount of [6-14C]glucose, carbon dioxide was the major end product, but at higher glucose concentrations mainly lactate was formed. This effect could be demonstrated in cercarial bodies in water as well as in fully transformed schistosomula. In non-transformed cercariae a change towards a more anaerobic energy metabolism could be induced by an increase in the external glucose concentration, which demonstrated that the biochemical transition can occur in the absence of the biological transformation. Furthermore, the biological transformation can occur without a concomitant biochemical transition: in the presence of 5 mM glucose, lactate production by cercarial bodies during transformation was increased 50-fold, whereas in the presence of only a tracer amount of glucose the metabolic profile remained that of cercariae. Also, in fully transformed schistosomula, this transition to a more anaerobic energy metabolism was induced by increased glucose concentrations, but at low glucose concentrations carbon dioxide was the major end product, as in cercariae. The effect of external glucose on the metabolism was fully reversible. After a high glucose concentration had induced a more anaerobic metabolism in cercariae in water, the metabolism returned to an aerobic one upon removal of the glucose. Likewise, the metabolism in schistosomula switched back and forth between anaerobic and aerobic patterns, following successive changes in the glucose concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

10 micron spectra of protostars and the solid methanol abundance

We have searched for the strong C-O stretching absorption of solid methanol near 9.8 micrometers toward the heavily obscured protostars AFGL 961, AFGL 2591, the BN object and Mon R2 IRS 3. There is no clear evidence for this feature in the spectra, resulting in very conservative upper limits to the methanol abundance of 6% to 17% relative to solid H2O toward these objects. This is well below previous estimates of 50%-80% obtained toward W33 A, NGC 7538 IRS 9, AFGL 2136, and W3 IRS 5, which were based on the assignment of the interstellar 6.85 micrometers absorption feature to the methanol C-H bending mode. This study shows that such high methanol abundances are not a characteristic of all interstellar ices.

Interstellar solid CO: polar and nonpolar interstellar ices

We present moderate-resolution (lambda/delta lambda approximately 1200) observations of the solid CO band in a sample of protostars. The spectra reveal two independent solid CO components along most lines of sight. One produces a narrow (delta nu approximately 5 cm-1) band generally centered at about 2140 cm-1 and the other a broader (delta nu approximately 10 cm-1) one at about 2136 cm-1. Both the peak position and width of the narrow, and generally strongest, component vary from object to object. The relative strengths of the two components vary considerably in this sample. Laboratory studies of the shape and peak position of the solid CO banD in astrophysically relevant mixtures show that the narrow CO band occurs in mixtures dominated by non-polar molecules (e.g., CO itself, CO2, O2, N2), while the broad feature is due to more polar mixtures, such as H2O ice. Calculations show that for mixtures dominated by CO (CO concentration > 0.3), the peak position and shape of the CO fundamental are strongly influenced by "surface modes," while for lower concentrations the laboratory measured absorption spectra provide very accurate representations of the small particle extinction spectrum. The observed variations in peak position and width of the interstellar 2140 cm-1 component can be attributed to variations in composition and/or physical characteristics of the grains (i.e., shape). These observations show that many lines of sight contain (at least) two independent grain mantle components: a polar mixture (H2O-rich) responsible for the 3.08 and 6.0 micrometers ice bands and a nonpolar one dominating the solid CO spectrum. These two independent grain mantle components may reflect chemical variations during accretion. Around luminous protostars, differences in volatility of the nonpolar and H2O-rich ices also may play an important role in determining their relative abundances.

[Neonatal blood group incompatibility due to anti-M antibodies]

Neonatal blood group antagonism due to anti-M antibodies is extremely rare. The case is reported of a neonate with moderately severe haemolytic anaemia due to anti-M which required two blood transfusions. Although anti-M antibodies are as a rule regarded as clinically irrelevant, and although they react almost exclusively at lower temperatures, they may in exceptional cases be demonstrated at 37 degrees C, as in the patient described; they may then cause haemolysis. Most strikingly, the direct Coombs test in this patient was negative; this phenomenon has been described before. In unexplained haemolytic anaemia of a newborn, even in the presence of a negative direct Coombs test, the possibility of blood group antagonism should be considered.

The interstellar C-H stretching band near 3.4 microns: constraints on the composition of organic material in the diffuse interstellar medium

To better constrain and quantify the composition of material in the diffuse interstellar medium (ISM), absorption spectra between 3600 and 2700 cm-1 (2.8 and 3.7 microns) have been taken of objects which have widely varying amounts of visual extinction along different lines of sight. The spectra of these objects contain a broad feature centered at approximately 3300 cm-1 (approximately 3.0 microns), attributed to O-H stretching vibrations, and/or a feature near 2950 cm-1 (3.4 microns) attributed to C-H stretching vibrations. The lack of correlation between the strengths of these two bands indicates that they do not arise from the same molecular carrier. The features in the 3100-2700 cm-1 (3.2-3.7 microns) region fall into one of two classes. We attribute the first class of features to material in the diffuse ISM on the basis of the similarity between the band profiles along the very different lines of sight to Galactic center source IRS 7 and VI Cygni #12. Similar features are also reported for Galactic center source IRS 3, Ve 2-45, and AFGL 2179. Higher resolution spectra of the objects OH 01-477 and T629-5, which are known to be M stars, are dominated by a series of narrow bands in this region. These bands are largely due to OH in the stars' photospheres. While the spectra of OH 01-477 and T629-5 are likely to contain C-H absorption from diffuse ISM dust, the strength of the overlapping photospheric OH features presently prevents us from quantifying the depths of the interstellar C-H feature towards these objects. The interstellar feature for Galactic center source IRS 7 has subpeaks near 2955, 2925, and 2870 cm-1 (+/- 5 cm-1), which we attribute to C-H stretching vibrations in the -CH2- and -CH3 groups of aliphatic hydrocarbons. These band positions fall within 5 cm-1 of the values normal for saturated aliphatics. The absence of a distinct band near 2855 cm-1 suggests that the material contains small amounts of electronegative groups like -O-H or -C triple bond N. The relative strengths and profiles of the 2955 and 2925 cm-1 features towards five objects suggests an average diffuse ISM line-of-sight -CH2-/-CH3 ratio of about 2.5, indicating the presence of relatively complex organic materials. The strengths of the subpeaks at 2925 and 2955 cm-1, due to -CH2- and -CH3 groups, respectively, correlate with visual extinction, strongly suggesting that the C-H stretching band is a general feature of the material along different lines of sight in the diffuse ISM. We find average ratios of A nu/tau(2925 cm-1) = 240 +/- 40 and A nu/tau(2955 cm-1) = 310 +/- 90 for the objects we have observed. We deduce that 2.6%-35% of the cosmic carbon in the ISM is tied up in the carrier of this band with the most likely value falling near 10%. The interstellar C-H band is remarkably similar to the feature in lab residues produced by irradiating analogs of dense molecular cloud ices. This is consistent with a model in which the hydrocarbon component in the diffuse interstellar medium consists of complex hydrocarbons containing aliphatic side chains and bridges which are produced in dense molecular clouds and subsequently modified in the diffuse medium.

The enigmatic presence of all gluconeogenic enzymes in Schistosoma mansoni adults

The activities of glucose-6-phosphatase (G6Pase), fructose-1,6-bisphosphatase (FBPase), phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC) were determined in homogenates of adult Schistosoma mansoni worms and compared with the activities in homogenates of rat liver and rat skeletal muscle, tissues with a high and a low gluconeogenic capacity, respectively. All four gluconeogenic enzymes were present in S. mansoni. The enzymes were less active than in rat liver, but the activities of G6Pase, PEPCK and PC were at least an order of magnitude higher than in rat skeletal muscle whereas FBPase was approximately equally active in S. mansoni and in rat muscle. Experiments with 14C-labelled substrates or [14C]NaHCO3 failed to demonstrate the actual occurrence of gluconeogenesis in S. mansoni. Some possible other functions of the gluconeogenic enzymes were investigated. Experiments with inhibitors of PEPCK gave no indications that this enzyme was involved in the degradation of glucose. This was confirmed by 13C-NMR experiments which indicated that lactate was formed from phosphoenolpyruvate via the actions of pyruvate kinase and lactate dehydrogenase, and that PEPCK did not participate in the formation of lactate. Substrate cycling between fructose-6-dehydrogenase, and fructose-1,6-bisphosphate was demonstrated to occur in adult S. mansoni. This shows that FBPase participates in the glucose metabolism of this parasite.

The transition from an aerobic to an anaerobic energy metabolism in transforming Schistosoma mansoni cercariae occurs exclusively in the head

It has been shown that in intact cercariae of Schistosoma mansoni in water, both head and tail had an identical, aerobic energy metabolism. As long as the environment was water, glucose was mainly degraded to carbon dioxide by both head and tail whether or not these two were still connected to each other. Transfer of intact cercariae into a simple salt medium supplemented with glucose resulted in a very rapid transition towards a more anaerobic energy metabolism: the production of lactate and pyruvate increased, whereas the production of carbon dioxide remained more or less constant. A concomitant rise in temperature to 37 degrees C was not essential for this biochemical transition, but made it more pronounced. Experiments on isolated cercarial bodies and tails in a transforming medium demonstrated that the tail oxidized glucose to carbon dioxide, whereas bodies produced mainly pyruvate and lactate. The results showed that the metabolic transition towards a more anaerobic energy metabolism occurred only in the head and not in the tail of the cercariae. Loss of the tail was shown not to be a pre-requisite for this transition, nor did it by itself trigger a metabolic switch in the resulting cercarial body.

The anomalous 3.43 and 3.53 micron emission features toward HD 97048 and Elias 1: C-C vibrational modes of polycyclic aromatic hydrocarbons?

We have obtained 5-8 microns spectra toward the two protostellar sources HD 97048 and Elias 1. Besides the well-known family of IR emission bands at 3.3, 6.2 "7.7," 8.7, and 11.3 microns, these objects show strong anomalous emission features at 3.43 and 3.53 microns. No related anomalous bands were found in the new spectra. Combining our results with earlier data, it is shown that, while the anomalous bands are emitted from within 0".05 (approximately 10 AU) of HD 97048, the emission in the general IR features is extended on at least a 20" scale. Some possible assignments of the anomalous emission features are discussed, namely C-H stretching modes in -CHO or -CH2-/-CH3 groups (either in dust grains or as sidegroups on polycyclic aromatic hydrocarbon molecules [PAHs]), and vibrational modes of PAHs without sidegroups. The absence of related anomalous emissions in the 5-8 microns region as well as the high-excitation conditions in the emission zone of the anomalous features make an origin in molecular (side-)groups in grains or on PAHs unlikely. Given the high energy density in the emission zone, as well as the apparent correspondence of the anomalous 3.43 and 3.53 microns features with weak emission shoulders associated with the general family of IR emission bands, it is concluded that an explanation in terms of C-C overtones and combination bands of highly excited, large PAHs or PACs (polycyclic aromatic carbons, i.e., dehydrogenated PAHs; > 500-1000 C atoms) is at the moment most attractive.