Comment on "Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime"

Dharma-wardana et al. [M. W. C. Dharma-wardana et al., Phys. Rev. E 96, 053206 (2017)2470-004510.1103/PhysRevE.96.053206] recently calculated dynamic electrical conductivities for warm dense matter as well as for nonequilibrium two-temperature states termed "ultrafast matter" (UFM) [M. W. C. Dharma-wardana, Phys. Rev. E 93, 063205 (2016)2470-004510.1103/PhysRevE.93.063205]. In this Comment we present two evident reasons why these UFM calculations are neither suited to calculate dynamic conductivities nor x-ray Thomson scattering spectra in isochorically heated warm dense aluminum. First, the ion-ion structure factor, a major input into the conductivity and scattering spectra calculations, deviates strongly from that of isochorically heated aluminum. Second, the dynamic conductivity does not show a non-Drude behavior which is an essential prerequisite for a correct description of the absorption behavior in aluminum. Additionally, we clarify misinterpretations by Dharma-wardana et al. concerning the conductivity measurements of Gathers [G. R. Gathers, Int. J. Thermophys. 4, 209 (1983)IJTHDY0195-928X10.1007/BF00502353].

X-ray scattering measurements of dissociation-induced metallization of dynamically compressed deuterium

Hydrogen, the simplest element in the universe, has a surprisingly complex phase diagram. Because of applications to planetary science, inertial confinement fusion and fundamental physics, its high-pressure properties have been the subject of intense study over the past two decades. While sophisticated static experiments have probed hydrogen's structure at ever higher pressures, studies examining the higher-temperature regime using dynamic compression have mostly been limited to optical measurement techniques. Here we present spectrally resolved x-ray scattering measurements from plasmons in dynamically compressed deuterium. Combined with Compton scattering, and velocity interferometry to determine shock pressure and mass density, this allows us to extract ionization state as a function of compression. The onset of ionization occurs close in pressure to where density functional theory-molecular dynamics (DFT-MD) simulations show molecular dissociation, suggesting hydrogen transitions from a molecular and insulating fluid to a conducting state without passing through an intermediate atomic phase.

Free-electron X-ray laser measurements of collisional-damped plasmons in isochorically heated warm dense matter

We present the first highly resolved measurements of the plasmon spectrum in an ultrafast heated solid. Multi-keV x-ray photons from the Linac Coherent Light Source have been focused to one micrometer diameter focal spots producing solid density aluminum plasmas with a known electron density of n_{e}=1.8×10^{23}  cm^{-3}. Detailed balance is observed through the intensity ratio of up- and down-shifted plasmons in x-ray forward scattering spectra measuring the electron temperature. The plasmon damping is treated by electron-ion collision models beyond the Born approximation to determine the electrical conductivity of warm dense aluminum.

Equilibration dynamics and conductivity of warm dense hydrogen

We investigate subpicosecond dynamics of warm dense hydrogen at the XUV free-electron laser facility (FLASH) at DESY (Hamburg). Ultrafast impulsive electron heating is initiated by a ≤ 300-fs short x-ray burst of 92-eV photon energy. A second pulse probes the sample via x-ray scattering at jitter-free variable time delay. We show that the initial molecular structure dissociates within (0.9 ± 0.2) ps, allowing us to infer the energy transfer rate between electrons and ions. We evaluate Saha and Thomas-Fermi ionization models in radiation hydrodynamics simulations, predicting plasma parameters that are subsequently used to calculate the static structure factor. A conductivity model for partially ionized plasma is validated by two-temperature density-functional theory coupled to molecular dynamic simulations and agrees with the experimental data. Our results provide important insights and the needed experimental data on transport properties of dense plasmas.

Resolving ultrafast heating of dense cryogenic hydrogen

We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300  fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9  ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory.

[Time of operative treatment of maldescensus testis in childhood - wishes and reality]

BACKGROUND

Maldescensus testis constitutes the most common diagnosis in the daily routine of a paediatric surgeon and is proved to be one of the most established risk factors for future infertility and malignancy.

MATERIAL AND METHODS

We examined therapy strategies of paediatricians in the catchment area of the University Clinic of Würzburg in the light of the late time of orchidopexy. This study consists of a short survey sent to 100 local paediatricians. After return, the given answers were put in comparison to the 504 cases of retentio testis treated in our clinic from 2005 to 2010.

RESULTS

Theoretical knowledge regarding guidelines for the treatment of retentio testis is abundant among paediatricians in and around Würzburg. Nevertheless, the initial therapy is of a hesitant character and often leads to an unnecessary delay in operation. The average age of boys receiving orchidopexy at our clinic between 2005 and 2010 amounted to 3.3 years.

CONCLUSION

Regarding guidelines the average age of cryptorchid boys receiving orchidopexy at the University Clinic of Würzburg was way too high between 2005 and 2010. To some extent this fact can be attributed to the hesitant manner of therapy shown by local paediatricians. An improvement in the time of operation is definitely possible and necessary in order to optimise the outcome.

Conformational studies on the Delta8(E,Z)-sphingolipid desaturase from Helianthus annuus with chiral fluoropalmitic acids as mechanistic probes

The Delta(8)-sphingolipid desaturase from sunflower (Helianthus annuus) converts phytosphinganine into a mixture of Delta(8)-(E)- and -(Z)-phytosphingenines by removal of two syn-hydrogen atoms from anti-, and gauche-conformations of the substrate. With chiral (R)-6-, (S)-6-, (R)-7-, and (S)-7-fluoropalmitic acids the importance of conformations for the formation of (E)- and (Z)-isomers was investigated by using growing yeast cells expressing the desaturase from H. annuus. The fluoropalmitic acids were readily incorporated into a series of fluorinated phytosphinganines. The desaturation products of the major C(18)-fluorophytosphinganine demonstrate that different conformations of the relevant aliphatic segment of the sphingolipids can be exposed to the active center of the enzyme resulting in (E)- or (Z)-fluoroalkenes. The presence of a fluorine atom at the position of the initial hydrogen removal C8-H(R) led to a complete suppression of the desaturation reaction, while replacement of C8-H(S) with fluorine generated a mixture of mainly (Z)- and trace amounts of (E)-fluoroolefine. Fluorine at C9 of the phytosphinganine precursors did not interfere with the initial C-H activation step and produced (E)- and (Z)-fluoroalkenes in the same ratio as observed for the nonfluorinated precursors. Hydroxylated byproducts of the desaturation process were not observed. These results strongly support the importance of conformations of the transition states during desaturation as the relevant criterion for the relative ratio of (E)- and (Z)-alkenes.

Thomson scattering on inhomogeneous targets

The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm dense matter states. For instance, a short-pulse optical laser irradiates a liquid hydrogen jet that is subsequently probed with brilliant soft x-ray radiation. The strongly inhomogeneous plasma prepared by the optical laser is characterized with particle-in-cell simulations. The interaction of the soft x-ray probe radiation for different time delays between pump and probe with the inhomogeneous plasma is also taken into account via radiative hydrodynamic simulations. We calculate the respective scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We can identify plasmon modes that are generated in different target regions and monitor their temporal evolution. Therefore, such pump-probe experiments are promising tools not only to measure the important plasma parameters density and temperature but also to gain valuable information about their time-dependent profile through the target. The method described here can be applied to various pump-probe scenarios by combining optical lasers and soft x ray, as well as x-ray sources.

Functional characterization of a higher plant sphingolipid Delta4-desaturase: defining the role of sphingosine and sphingosine-1-phosphate in Arabidopsis

The role of Delta4-unsaturated sphingolipid long-chain bases such as sphingosine was investigated in Arabidopsis (Arabidopsis thaliana). Identification and functional characterization of the sole Arabidopsis ortholog of the sphingolipid Delta4-desaturase was achieved by heterologous expression in Pichia pastoris. A P. pastoris mutant disrupted in the endogenous sphingolipid Delta4-desaturase gene was unable to synthesize glucosylceramides. Synthesis of glucosylceramides was restored by the expression of Arabidopsis gene At4g04930, and these sphingolipids were shown to contain Delta4-unsaturated long-chain bases, confirming that this open reading frame encodes the sphingolipid Delta4-desaturase. At4g04930 has a very restricted expression pattern, transcripts only being detected in pollen and floral tissues. Arabidopsis insertion mutants disrupted in the sphingolipid Delta4-desaturase At4g04930 were isolated and found to be phenotypically normal. Sphingolipidomic profiling of a T-DNA insertion mutant indicated the absence of Delta4-unsaturated sphingolipids in floral tissue, also resulting in the reduced accumulation of glucosylceramides. No difference in the response to drought or water loss was observed between wild-type plants and insertion mutants disrupted in the sphingolipid Delta4-desaturase At4g04930, nor was any difference observed in stomatal closure after treatment with abscisic acid. No differences in pollen viability between wild-type plants and insertion mutants were detected. Based on these observations, it seems unlikely that Delta4-unsaturated sphingolipids and their metabolites such as sphingosine-1-phosphate play a significant role in Arabidopsis growth and development. However, Delta4-unsaturated ceramides may play a previously unrecognized role in the channeling of substrates for the synthesis of glucosylceramides.

Identification and functional characterization of the 2-hydroxy fatty N-acyl-Delta3(E)-desaturase from Fusarium graminearum

Delta3(E)-unsaturated fatty acids are characteristic components of glycosylceramides from some fungi, including also human- and plant-pathogenic species. The function and genetic basis for this unsaturation is unknown. For Fusarium graminearum, which is pathogenic to grasses and cereals, we could show that the level of Delta3-unsaturation of glucosylceramide (GlcCer) was highest at low temperatures and decreased when the fungus was grown above 28 degrees C. With a bioinformatics approach, we identified a new family of polypeptides carrying the histidine box motifs characteristic for membrane-bound desaturases. One of the corresponding genes was functionally characterized as a sphingolipid-Delta3(E)-desaturase. Deletion of the candidate gene in F. graminearum resulted in loss of the Delta3(E)-double bond in the fatty acyl moiety of GlcCer. Heterologous expression of the corresponding cDNA from F. graminearum in the yeast Pichia pastoris led to the formation of Delta3(E)-unsaturated GlcCer.

A higher plant delta8 sphingolipid desaturase with a preference for (Z)-isomer formation confers aluminum tolerance to yeast and plants

Three plant cDNA libraries were expressed in yeast (Saccharomyces cerevisiae) and screened on agar plates containing toxic concentrations of aluminum. Nine cDNAs were isolated that enhanced the aluminum tolerance of yeast. These cDNAs were constitutively expressed in Arabidopsis (Arabidopsis thaliana) and one cDNA from the roots of Stylosanthes hamata, designated S851, conferred greater aluminum tolerance to the transgenic seedlings. The protein predicted to be encoded by S851 showed an equally high similarity to Delta6 fatty acyl lipid desaturases and Delta8 sphingolipid desaturases. We expressed other known Delta6 desaturase and Delta8 desaturase genes in yeast and showed that a Delta6 fatty acyl desaturase from Echium plantagineum did not confer aluminum tolerance, whereas a Delta8 sphingobase desaturase from Arabidopsis did confer aluminum tolerance. Analysis of the fatty acids and sphingobases of the transgenic yeast and plant cells demonstrated that S851 encodes a Delta8 sphingobase desaturase, which leads to the accumulation of 8(Z/E)-C(18)-phytosphingenine and 8(Z/E)-C(20)-phytopshingenine in yeast and to the accumulation of 8(Z/E)-C(18)-phytosphingenine in the leaves and roots of Arabidopsis plants. The newly formed 8(Z/E)-C(18)-phytosphingenine in transgenic yeast accounted for 3 mol% of the total sphingobases with a 8(Z):8(E)-isomer ratio of approximately 4:1. The accumulation of 8(Z)-C(18)-phytosphingenine in transgenic Arabidopsis shifted the ratio of the 8(Z):8(E) isomers from 1:4 in wild-type plants to 1:1 in transgenic plants. These results indicate that S851 encodes the first Delta8 sphingolipid desaturase to be identified in higher plants with a preference for the 8(Z)-isomer. They further demonstrate that changes in the sphingolipid composition of cell membranes can protect plants from aluminum stress.

Plasma membrane lipid alterations induced by cold acclimation and abscisic acid treatment of winter wheat seedlings differing in frost resistance

Cold acclimation of plants affects many aspects of metabolism. Changes in plasma membrane lipids have always been considered to be important for development of frost resistance and survival at subzero temperatures. We studied different cultivars of winter wheat (Triticum aestivum L.) that differed in frost resistance induced either by cold acclimation or treatment with the plant hormone abscisic acid (ABA). Plasma membranes were isolated from non-acclimated and cold- as well as from ABA-acclimated plants, and were subjected to detailed lipid analysis. Cold acclimation affected virtually all plasma membrane lipid components and their constituents, resulting in both increases and decreases, which varied between the three groups of plants investigated. Including the cold-induced variations observed in the few plant species studied in detail previously, cerebrosides were the only components reduced by cold acclimation in all plants. In wheat, more uniform and consistent patterns were obtained when considering colligative parameters such as total free sterols, phospholipids or glycolipids, either as the proportion of total lipids or based on plasma membrane protein. The parameter which changed most significantly in parallel to the increase of inducible frost resistance in the three groups of plants was the ratio of free sterols/glycolipids, which increased. ABA treatment resulted in qualitatively similar effects in only one cultivar, but in general these changes were less pronounced. Compared to changes in transcription rates of several cold-induced genes and in the concentration of various compatible solutes reported for other plants, the observed changes in plasma membrane lipids are minor ones. This may indicate that acclimation-induced changes can be accomplished by posttranscriptional regulation of enzymatic activities, which is in agreement with the failure to detect significant changes in transcription of the corresponding genes during cold induction.

A possible role of sphingolipids in the aluminium resistance of yeast and maize

The plasma membrane is most likely the major target for sensing of aluminium (Al), leading to inhibition of plant root-growth. As a result of high external Al, alterations in plasma membrane composition may be expected in order to maintain its properties. As sphingolipids are characteristic components of this membrane, their involvement in membrane adjustment to increased Al concentrations was investigated. Heterologous expression of a stereounselective long-chain base (LCB) (8E/Z)-desaturase from Arabidopsis thaliana, Brassica napus and Helianthus annuus in Saccharomyces cerevisiae improved the Al resistance of the transgenic yeast cells. This encouraged us to investigate whether Al affects the LCB composition, and whether genetic engineering of the LCB profile modifies the Al resistance of the Al-sensitive plant species maize (Zea mays, L.). Constitutive expression of the LCB (8E/Z)-desaturase from Arabidopsis thaliana in maize roots led to an 8- to 10-fold increase in (8E)-4-hydroxysphing-8-enine in total roots. Less marked but similar changes were observed in 3 mm root apices. Al treatment of the Al-sensitive maize cv Lixis resulted in a significant increase in the proportion of (8Z)-LCB and in the content of total LCBs in root tips, which was not observed in the Al-resistant cv ATP-Y. When root tips of transgenic plants were exposed to Al, only minor changes of both (8Z)- and (8E)-unsaturated LCBs as well as of the total LCB were observed. Al treatment of the wild type parental line H99 decreased the (8Z)-unsaturated LCBs and the total LCB content. Based on Al-induced callose production, a marker for Al sensitivity, the parental line H99 was as Al-resistant as cv ATP-Y, whereas the transgenic line became as sensitive as cv Lixis. Taken together, these data suggest that, in particular, the loss of the ability to down-regulate the proportion of (8Z)-unsaturated LCBs may be related to increased Al sensitivity.

Identification of fungal sphingolipid C9-methyltransferases by phylogenetic profiling

Fungal glucosylceramides play an important role in plant-pathogen interactions enabling plants to recognize the fungal attack and initiate specific defense responses. A prime structural feature distinguishing fungal glucosylceramides from those of plants and animals is a methyl group at the C9-position of the sphingoid base, the biosynthesis of which has never been investigated. Using information on the presence or absence of C9-methylated glucosylceramides in different fungal species, we developed a bioinformatics strategy to identify the gene responsible for the biosynthesis of this C9-methyl group. This phylogenetic profiling allowed the selection of a single candidate out of 24-71 methyltransferase sequences present in each of the fungal species with C9-methylated glucosylceramides. A Pichia pastoris knock-out strain lacking the candidate sphingolipid C9-methyltransferase was generated, and indeed, this strain contained only non-methylated glucosylceramides. In a complementary approach, a Saccharomyces cerevisiae strain was engineered to produce glucosylceramides suitable as a substrate for C9-methylation. C9-methylated sphingolipids were detected in this strain expressing the candidate from P. pastoris, demonstrating its function as a sphingolipid C9-methyltransferase. The enzyme belongs to the superfamily of S-adenosylmethionine-(SAM)-dependent methyltransferases and shows highest sequence similarity to plant and bacterial cyclopropane fatty acid synthases. An in vitro assay showed that sphingolipid C9-methylation is membrane-bound and requires SAM and Delta4,8-desaturated ceramide as substrates.

Are glucocerebrosides the predominant sphingolipids in plant plasma membranes?

Long-chain sphingobases have been analyzed in various fractions prepared from different organs (leaf, root, storage tissue) from five dicotyledoneous plants (Arabidopsis thaliana, Brassica oleracea, Nicotiana tabacum, Pisum sativum, Spinacia oleracea). The resulting sphingobase profiles from cerebrosides and plasma membranes (PMs) show large qualitative and quantitative differences. Assuming that cerebrosides from all cellular membranes have similar sphingobase profiles, these data suggest that cerebrosides, considered to be characteristic glycolipids of plant PMs and specified by large proportions of sphingobases with an 8Z-double bond motif, do not represent the major sphingolipids of PMs. The fraction of unidentified complex sphingolipids, containing mainly 8E-phytosphingenine, exceeds the cerebroside proportion in PMs by several factors and may be as abundant as diacylglycerol-based phospholipids. These results are discussed with respect to the distribution of various lipids between the bilayer halves of plant PM.

Novel fatty acid elongases and their use for the reconstitution of docosahexaenoic acid biosynthesis

In algae, the biosynthesis of docosahexaenoic acid (22:6omega3; DHA) proceeds via the elongation of eicosapentaenoic acid (20:5omega3; EPA) to 22:5omega3, which is required as a substrate for the final Delta4 desaturation. To isolate the elongase specific for this step, we searched expressed sequence tag and genomic databases from the algae Ostreococcus tauri and Thalassiosira pseudonana, from the fish Oncorhynchus mykiss, from the frog Xenopus laevis, and from the sea squirt Ciona intestinalis using as a query the elongase sequence PpPSE1 from the moss Physcomitrella patens. The open reading frames of the identified elongase candidates were expressed in yeast for functional characterization. By this, we identified two types of elongases from O. tauri and T. pseudonana: one specific for the elongation of (Delta6-)C18-PUFAs and one specific for (Delta5-)C20-PUFAs, showing highest activity with EPA. The clones isolated from O. mykiss, X. laevis, and C. intestinalis accepted both C18- and C20-PUFAs. By coexpression of the Delta6- and Delta5-elongases from T. pseudonana and O. tauri, respectively, with the Delta5- and Delta4-desaturases from two other algae we successfully implemented DHA synthesis in stearidonic acid-fed yeast. This may be considered an encouraging first step in future efforts to implement this biosynthetic sequence into transgenic oilseed crops.

Stereochemistry of a bifunctional dihydroceramide delta 4-desaturase/hydroxylase from Candida albicans; a key enzyme of sphingolipid metabolism

The stereochemical course of the dihydroceramide delta 4-(E)-desaturase from Candida albicans, cloned and expressed in the yeast Saccharomyces cerevisiae strain sur2 delta, was determined using stereospecifically labelled (2R,3S)-[2,3,4,4-2H4]-palmitic acid as a metabolic probe. Mass spectrometric analysis of the dinitrophenyl-derivatives of the labelled long-chain bases revealed elimination of a single deuterium atom from C(4) (corresponding to the C(4)-HR) along with a hydrogen atom from C(5) (corresponding to the C(5)-HS). This finding is consistent with an overall syn-elimination of the two vicinal hydrogen atoms. Besides the desaturation product sphingosine (93%) minor amounts of a 4-hydroxylated product (phytosphinganine, 7%) were identified that classify the Candida enzyme as a bifunctional desaturase/hydroxylase. Both processes, desaturation and hydroxylation proceed with loss of C(4)-HR from the chiral precursor. This finding is in agreement with a two-step process involving activation of the substrate by removal of the C(4)-HR to give a C-centred radical or radicaloid followed by either disproportionation into an olefin, water and a reduced diiron complex, or to recombination of the primary reactive intermediate with an active site-bound oxygen to yield a secondary alcohol. This result demonstrates the close mechanistic relationship between desaturation and hydroxylation as two different reaction pathways of a single enzyme and strengthens the mechanistic relationship of desaturases from fatty acid metabolism and sphingolipids.

Plant sphingolipids: structural diversity, biosynthesis, first genes and functions

In mammals and Saccharomyces cerevisiae, sphingolipids have been a subject of intensive research triggered by the interest in their structural diversity and in mammalian pathophysiology as well as in the availability of yeast mutants and suppressor strains. More recently, sphingolipids have attracted additional interest, because they are emerging as an important class of messenger molecules linked to many different cellular functions. In plants, sphingolipids show structural features differing from those found in animals and fungi, and much less is known about their biosynthesis and function. This review focuses on the sphingolipid modifications found in plants and on recent advances in the functional characterization of genes gaining new insight into plant sphingolipid biosynthesis. Recent studies indicate that plant sphingolipids may be also involved in signal transduction, membrane stability, host-pathogen interactions and stress responses.

Identification and characterization of a sphingolipid delta 4-desaturase family

Sphingolipids desaturated at the Delta4-position are important signaling molecules in many eukaryotic organisms, including mammals. In a bioinformatics approach, we now identified a new family of protein sequences from animals, plants, and fungi and characterized these sequences biochemically by expression in Saccharomyces cerevisiae. This resulted in the identification of the enzyme sphingolipid Delta4-desaturase (dihydroceramide desaturase) from Homo sapiens, Mus musculus, Drosophila melanogaster, and Candida albicans, in addition to a bifunctional sphingolipid Delta4-desaturase/C-4-hydroxylase from M. musculus. Among the sequences investigated are the Homo sapiens membrane lipid desaturase, the M. musculus degenerative spermatocyte, and the Drosophila melanogaster degenerative spermatocyte proteins. During spermatogenesis, but not oogenesis of des mutant flies, both cell cycle and spermatid differentiation are specifically blocked at the entry into the first meiotic division, leading to male sterility. This mutant phenotype can be restored to wild-type by complementation with a functional copy of the des gene (Endo, K., Akiyama, T., Kobayashi S., and Okada, M. (1996) Mol. Gen. Genet. 253, 157-165). These results suggest that Delta4-desaturated sphingolipids provide an early signal necessary to trigger the entry into both meiotic and spermatid differentiation pathways during Drosophila spermatogenesis.

[A delayed life-threatening complication after uneventful varicella infection: transient complete heart block]

A 9 year old boy presented with uncharacteristic gastroenteric complaints due to a complete heart block 9 days after an uneventful varicella infection. Echocardiographically there were no signs of gross myocardial involvement. Bradydysrhythmia necessitated isoproterenol application however without the need for temporary transvenous cardiac pacing. After a short period of second-degree atrioventricular block and transient left bundle branch block the rhythm recovered completely and sinus rhythm is maintained so far. Worrying is the delayed onset of this complication after an uneventful course of a typically undangerous children's disease. Presumably a remaining inflammatory reaction in different parts of the specific conducting system has to be assumed. The long lasting prognosis of the atrioventricular conduction properties remains to be seen.

Metal-mediated reactions modeled after nature

The Collaborative Research Center (CRC) 436 'Metal-Mediated Reactions Modeled after Nature' was founded for the express purpose of analyzing the catalytic principles of metallo-enzymes in order to construct efficient catalysts on a chemical basis. The structure of the active center and neighboring chemical environment in enzymes serves as a focal point for developing reactivity models for the chemical redesign of catalysts. Instead of simply copying enzyme construction, we strive to achieve new chemical intuition based on the results of long-lasting natural evolution. We hope for success, since nature uses a limited set of building blocks, whereas we can apply the full repertoire of chemistry. Key substrates in this approach are small molecules, such as CO2, O2 NO3- and N2. Nature complexes these substrates, activates them and performs chemical transformations--all within the active center of a metalloenzyme. In this article, we report on some aspects and first results of the Collaborative Research Center (CRC) 436, such as nitrate reductase, sphingolipid desaturase, carbonic anhydrase, leucine aminopeptidase and dopamine beta-monooxygenase.

Improvement of perineal wound healing by local administration of gentamicin-impregnated collagen fleeces after abdominoperineal excision of rectal cancer

BACKGROUND

Despite significant advancements in rectal surgery, poor perineal wound healing after abdominoperineal resection (APR) of the anorectum continues to be a potential complication of the procedure. The aim of this prospective randomized multicenter study was to investigate the efficacy of a new mode of local antibiotic administration.

PATIENTS AND METHODS

Ninety-seven patients who had to undergo APR for low rectal carcinoma either received sacral drainage plus primary wound closure (control group, n = 48) or the same treatment and supplementary application of three resorbable gentamicin-impregnated collagen fleeces (Septocoll; Merck Biomaterial GmbH, Darmstadt, Germany; Genta group, 49). The following target criteria were investigated: bacteriologic efficacy with respect to the eradication of Enterobacteriaceae, Staphylococcus, and Pseudomonas organisms, and clinical efficacy with respect to perineal wound healing.

RESULTS

The Genta group showed a marked reduction in the investigated pathogens from the secretion obtained by sacral drainage on days 1 and 3, as well as high gentamicin concentrations (day 1, median 126.2 microg/mL; day 3, median 97.6 microg/mL). In total, bacteriologic efficacy amounted to 83.7% in the Genta group (41 of 49 patients) versus 60.4% (29 of 48 patients) in controls (P = 0.013). In concurrence with these bacteriologic results, the postoperative infection rate was significantly higher in controls: 10 patients (20.83%) in the control group versus 3 (6.1%) in the Genta group developed perineal or sacral infection (P <0.05). Postoperative complications in the recruited patients revealed no indication of gentamicin-induced adverse reactions.

CONCLUSIONS

The results of the study show that the specified dose of 3 Septocoll fleeces in patients with APR is liable to significantly eliminate enterobacteria, staphylococci, and pseudomonads. The clinical course is improved as a result of the bactericidal effect exerted by the gentamicin fleece. The use of Septocoll reduced the incidence of postoperative perineal and sacral infections. Local antibiotic carriers seem to be of great advantage in poorly perfused areas such as the sacral cavity or anatomically problematic regions as the rima ani. In locally contaminated or infected areas, local antibiotic carriers achieve greater concentrations of the active substance than those achieved with systemic antibiotics, even if the latter are administered by the parenteral route.

Increasing the efficiency and flexibility of capital funding for public and private hospitals

This paper outlines the recent history of capital funding in the health sector in Australia. It focuses on the trends in capital expenditures and the roles of the public and private sectors. The demand for future capital funding will depend upon a number of factors, including the state of the current capital stock and uncertain future impacts of technology and changes in patient demands. Because of these uncertainties, capital funding for the future must be flexible to meet any changes in operations and demand. The paper highlights the possible use of joint ventures between various public and private organisations, based on the principles of competition and cooperation.

Functional characterization of sphingolipid C4-hydroxylase genes from Arabidopsis thaliana

In the genome of Arabidopsis thaliana, two genes were identified encoding isoenzymes for C4-hydroxylation of long chain bases (LCB) in plant sphingolipids. Both predicted proteins consist of 258 amino acid residues (77% identity) which show sequence similarity to di-iron-binding enzymes, such as Sur2p and Erg3p from yeast, involved in oxygen-dependent lipid modifications. Heterologous expression of these genes in a yeast sur2Delta-null mutant lacking C4-LCB hydroxylation resulted in the formation of D-ribo-C(18)- and -C(20)-phytosphinganine. The identity and stereochemical configuration of the isolated trihydroxybases was confirmed by electrospray ionization-mass spectroscopy, gas-liquid chromatography-mass spectrometry and 1H-nuclear magnetic resonance spectroscopy. These results represent the first functional identification of SUR2 genes from plants as well as from any organism other than yeast.

Functional Identification of a Δ8-Sphingolipid Desaturase from Borago officinalis

The similarities between delta12- and delta5-fatty acyl desaturase sequences were used to construct degenerate primers for PCR experiments with cDNA transcribed from mRNA of developing borage seeds. Screening of a borage seed cDNA library with an amplified DNA fragment resulted in the isolation of a full-length cDNA corresponding to a deduced open-reading frame of 446 amino acids. The protein showed high similarity to plant delta8-sphingolipid desaturases as well as to the delta6-fatty acyl desaturase from Borago officinalis. The sequence is characterized by the presence of a N-terminal cytochrome b5 domain. Expression of this open-reading frame in Saccharomyces cerevisiae resulted in the formation of delta8-trans/cis-phytosphingenines not present in wild-type cells, as shown by HPLC analysis of sphingoid bases as their dinitrophenyl derivatives. GLC-MS analysis of the methylated di-O-trimethylsilyl ether derivatives confirmed the presence of delta8-stereoisomers of C18- and C20-phytosphingenine. Furthermore, Northern blotting showed that the gene encoding a stereo-unselective delta8-sphingolipid desaturase is primarily expressed in young borage leaves.

Further characterization of Delta(8)-sphingolipid desaturases from higher plants

A previously cloned cDNA from Helianthus annuus codes for a fusion protein composed of an N-terminal cytochrome b(5) and a C-terminal desaturase domain. For a functional identification, this cDNA was expressed in Saccharomyces cerevisiae and the structures of sphingolipid long-chain bases were analysed. The expression of this sunflower enzyme resulted in the formation of new Delta(8)-trans/cis-phytosphingenine from C(18)- and C(20)-phytosphinganine present in wild-type yeast cells. To elucidate the substrate specificity, the recently cloned Delta(8)-sphingolipid desaturases from Arabidopsis thaliana and Brassica napus were expressed in the yeast mutant sur2Delta that lacked the sphinganine C(4)-hydroxylase and was thus unable to form phytosphinganine. Long-chain base analysis of the transformed mutant cells did not show any conversion of C(18)- or C(20)-sphinganine into Delta(8)-sphingenine, whereas exogenously added C(18)-phytosphinganine was desaturated to Delta(8)-trans/cis-phytosphingenine. Furthermore, GLC-MS analysis did not reveal the presence of any Delta(9)-regioisomers as reported before. These results show that the sunflower gene codes for a Delta(8)-sphingolipid desaturase which accepts C(18)- and C(20)-phytosphinganine. The absence of Delta(8)-sphingenine as desaturation product in the transformed mutant suggests that C(4)-hydroxylation of sphinganine precedes Delta(8)-desaturation. Therefore, in yeast, the substrate for the plant Delta(8)-sphingolipid desaturase seems to be the phytosphinganine residue.

A bifunctional delta-fatty acyl acetylenase/desaturase from the moss Ceratodon purpureus. A new member of the cytochrome b5 superfamily

Many plant genes have been cloned that encode regioselective desaturases catalyzing the formation of cis-unsaturated fatty acids. However, very few genes have been cloned that encode enzymes catalyzing the formation of the functional groups found in unusual fatty acids (e.g. hydroxy, epoxy or acetylenic fatty acids). Here, we describe the characterization of an acetylenase from the moss Ceratodon purpureus with a regioselectivity differing from the previously described Delta12-acetylenase. The gene encoding this protein, together with a Delta6-desaturase, was cloned by a PCR-based approach with primers derived from conserved regions in Delta5-, Delta6-fatty-acid desaturases and Delta8-sphingolipid desaturases. The proteins that are encoded by the two cloned cDNAs are likely to consist of a N-terminal extension of unknown function, a cytochrome b5-domain, and a C-terminal domain that is similar to acyl lipid desaturases with characteristic histidine boxes. The proteins were highly homologous in sequence to the Delta6-desaturase from the moss Physcomitrella patens. When these two cDNAs were expressed in Saccharomyces cerevisiae, both transgenic yeast cultures desaturated Delta9-unsaturated C16- and C18-fatty acids by inserting an additional Delta6cis-double bond. One of these transgenic yeast clones was also able to introduce a Delta6-triple bond into gamma-linolenic and stearidonic acid. This resulted in the formation of 9,12,15-(Z,Z,Z)-octadecatrien-6-ynoic acid, the main fatty acid found in C. pupureus. These results demonstrate that the Delta6-acetylenase from C. pupureus is a bifunctional enzyme, which can introduce a Delta6cis-double bond into 9,12,(15)-C18-polyenoic acids as well as converting a Delta6cis-double bond to a Delta6-triple bond.

A sphingolipid desaturase from higher plants. Identification of a new cytochrome b5 fusion protein

A recently cloned cDNA from sunflower codes for a fusion protein composed of an N-terminal cytochrome b5 and a domain similar to membrane-bound acyl lipid desaturases. For a functional identification, homologous cDNAs from Brassica napus and Arabidopsis thaliana were expressed in Saccharomyces cerevisiae, and sphingolipid long chain bases were analyzed. The expression of the heterologous enzyme results in significant proportions of new Delta8, 9-cis/trans-phytosphingenines that accompany the residual C18-phytosphinganine predominating in wild-type yeast cells. These results represent the first identification of a gene coding for a sphingolipid desaturase and for a stereounselective desaturase showing trans-activity from any organism. Furthermore, this fusion protein is a new member of the cytochrome b5 superfamily. The formation of the two regioisomeric phytosphingenines in the transformed yeast sheds new light on the factors controlling regioselectivity.

The relationship of school breakfast to psychosocial and academic functioning: cross-sectional and longitudinal observations in an inner-city school sample

OBJECTIVE

To determine if a relationship exists between participation in a school breakfast program and measures of psychosocial and academic functioning in school-aged children.

METHODS

Information on participation in a school breakfast program, school record data, and in-depth interviews with parents and children were collected in 1 public school in Philadelphia, Pa, and 2 public schools in Baltimore, Md, prior to the implementation of a universally free (UF) breakfast program and again after the program had been in place for 4 months. One hundred thirty-three low-income students had complete data before and after the UF breakfast program on school breakfast participation and school-recorded measures, and 85 of these students had complete psychosocial interview data before and after the UF breakfast program. Teacher ratings of behavior before and after the UF breakfast program were available for 76 of these students.

RESULTS

Schoolwide data showed that prior to the UF breakfast program, 240 (15%) of the 1627 students in the 3 schools were eating a school-supplied breakfast each day. Of the 133 students in the interview sample, 24 (18%) of the students ate a school-supplied breakfast often, 26 (20%) ate a school-supplied breakfast sometimes, and 83 (62%) ate a school-supplied breakfast rarely or never. Prior to the UF breakfast program, students who ate a school-supplied breakfast often or sometimes had significantly higher math scores and significantly lower scores on child-, parent-, and teacher-reported symptom questionnaires than children who ate a school-supplied breakfast rarely or never. At the end of the school term 4 months after the implementation of the UF breakfast program, school-supplied breakfast participation had nearly doubled and 429 (27%) of the 1612 children in the 3 schools were participating in the school breakfast program each day. In the interview sample, almost half of the children had increased their participation. Students who increased their participation in the school breakfast program had significantly greater increases in their math grades and significantly greater decreases in the rates of school absence and tardiness than children whose participation remained the same or decreased. Child and teacher ratings of psychosocial problems also decreased to a significantly greater degree for children with increased participation in the school breakfast program.

CONCLUSION

Both cross-sectional and longitudinal data from this study provide strong evidence that higher rates of participation in school breakfast programs are associated in the short-term with improved student functioning on a broad range of psychosocial and academic measures.

Effects of gestational and postnatal age on body temperature, oxygen consumption, and activity during early skin-to-skin contact between preterm infants of 25-30-week gestation and their mothers

Temporary skin-to-skin contact between preterm infant and the mother is increasingly used in neonatal medicine to promote bonding. It is not known at which gestational age (GA) and postnatal age skin-to-skin contact outside the incubator is a sufficiently warm environment and is tolerated by preterm infants without a decrease in body temperature, oxygen consumption (VO2) increase, or unrest. We conducted a prospective clinical study of 27 spontaneously breathing preterm infants of 25-30-wk GA. Rectal temperature (Trecta), VO2 (indirect calorimetry), and activity were continuously measured in the incubator (60 min), during skin-to-skin contact (60 min), and back in the incubator (60 min) in wk 1 and 2 of life. In wk 1 the change in Trectal during skin-to-skin contact was related to GA (r=0.585, p=0.0027): infants of 25-27-wk GA lost heat during skin-to-skin contact, whereas infants of 28-30 wk gained heat and their mean Trectal during skin-to-skin contact was 0.3 degrees C higher than before (p < 0.01). No significant changes of VO2 or activity occurred. In wk 2 the infants' VO2 was higher than in wk 1, but VO2 during skin-to-skin contact was the same as in the incubator. Only small fluctuations in Trectal occurred. In wk 2 all infants slept more during skin-to-skin contact than in the incubator (p < 0.02). We conclude that, for preterm infants of 28-30-wk GA, skin-to-skin contact was a sufficiently warm environment as early as postnatal wk 1. For infants of 25-27-wk GA skin-to-skin contact should be postponed until wk 2 of life, when their body temperature remains stable and they are more quiet during skin-to-skin contact than in the incubator.

Fatty acid elongation in yeast--biochemical characteristics of the enzyme system and isolation of elongation-defective mutants

Elongation of long-chain fatty acids was investigated in yeast mutants lacking endogenous de novo fatty acid synthesis. In this background, in vitro fatty acid elongation was dependent strictly on the substrates malonyl-CoA, NADPH and a medium-chain or long-chain acyl-CoA primer of 10 or more carbon atoms. Maximal activity was observed with primers containing 12-14 carbon atoms, while shorter-chain-length acyl-CoA were almost (octanoyl-CoA) or completely (hexanoyl-CoA, acetyl-CoA) inactive. In particular, acetyl-CoA was inactive as a primer and as extender unit. The Michaelis constants for octanoyl-CoA (0.33 mM), decanoyl-CoA (0.83 mM) lauroyl-CoA (0.05 mM), myristoyl-CoA (0.4 mM) and palmitoyl-CoA (0.13 mM) were determined and were comparable for fatty acid synthesis and elongation. In contrast, the affinity of malonyl-CoA was 17-fold lower for elongation (Km = 0.13 mM) than for the fatty acid synthase (FAS) system. With increasing chain length of the primer (> or = 12:0), fatty acid elongation becomes increasingly sensitive to substrate inhibition. Due to the activation of endogenous fatty acids, ATP exhibits a stimulatory effect at suboptimal but not at saturating substrate concentrations. In the yeast cell homogenate, the specific activity of fatty acid elongation is about 10-20-fold lower than that of de novo fatty acid synthesis. The same elongation activity is observed in respiratory competent and in mitochondrially defective cells. The products of in vitro fatty acid elongation are fatty acids of 15-17 or 22-26 carbon atoms, depending on whether tridecanoyl-CoA or stearoyl-CoA is used as a primer. In vitro, the elongation products are converted in part, by alpha-oxidation, to their odd-chain-length lower homologues or are hydrolyzed to fatty acids. In contrast, no odd-chain-length elongation products or very-long-chain fatty acids (VLCFA) shorter than 26:0 are observed in vivo. Hence, VLCFA synthesis exhibits a higher processivity in vivo than in the cell homogenate. In addition, the in vivo process appears to be protected against side reactions such as hydrolysis or alpha-oxidation. Yeast mutants defective in 12:0 or 13:0 elongation were derived from fas-mutant strains according to their failure to grow on 13:0-supplemented media. In vivo, 12:0 elongation was reduced to 0-10% of the normal level, while 16:0 elongation and VLCFA synthesis were unimpaired. It is concluded that yeast contains either two different elongation systems, or that the respective mutation interferes differentially with medium-chain and long-chain fatty acid elongation. The yeast gene affected in the elongation-defective mutants was isolated and, upon sequencing, identified as the known ELO1 sequence. It encodes a putative membrane protein of 32-kDa molecular mass with no obvious similarity to any of the known FAS component enzymes.

Body temperatures and oxygen consumption during skin-to-skin (kangaroo) care in stable preterm infants weighing less than 1500 grams

BACKGROUND

More and progressively smaller preterm infants are taken out of the incubator and placed skin to skin on their mother's chest to promote bonding, despite concerns that the infants are exposed to cold during this intervention.

OBJECTIVE

To test the hypothesis that skin-to-skin care is a cold stress for preterm infants weighing less than 1500 gm, with a decrease in rectal temperature, a decrease in peripheral skin temperature, or an increase in oxygen consumption compared with conditions monitored during incubator care.

STUDY DESIGN

We studied 22 stable, spontaneously breathing preterm infants weighing less than 1500 gm (appropriate in size for gestational age), who had their first skin-to-skin care in the first week of life. We continuously measured rectal temperature, peripheral skin temperature (foot), and oxygen consumption (indirect calorimetry) for 1 hour in a thermoneutral incubator, during 1 hour of skin-to-skin care, and for another hour in the incubator. Mean values for the three periods were compared by analysis of variance.

RESULTS

During skin-to-skin care the mean rectal temperature was 0.2 degree C (p < 0.01) and the peripheral skin temperature was 0.6 degree C (p < 0.01) higher than during the preceding hour in the incubator. Back in the incubator, body temperatures returned to values recorded before skin-to-skin care. Oxygen consumption during skin-to-skin care (6.1 +/- 0.9 ml/kg per minute) was not significantly higher than in the incubator (5.8 +/- 0.8 ml/kg per minute).

CONCLUSION

For stable preterm infants weighing less than 1500 gm and less than 1 week of age, 1 hour of skin-to-skin care is not a cold stress compared with care in a thermoneutral incubator.

Comparison of face mask, head hood, and canopy for breath sampling in flow-through indirect calorimetry to measure oxygen consumption and carbon dioxide production of preterm infants < 1500 grams

Complete sampling of expired air is essential for accurate O2 consumption(CO2 production) [VO2(VCO2)] measurements with flow-through indirect calorimetry. In preterm infants complete sampling is critical, because only low sampling flows can be used. The accuracy of the various breath sampling systems at low flows and their patient compatibility is untested. We therefore measured 1) the accuracy of VO2(VCO2) measurements with a face mask, a head hood, and a canopy in vitro at low sampling flows; 2) the effect of breathing on measurements with the face mask; and 3) the effect of breath sampling systems on activity and body temperature of preterm infants. VO2(VCO2) were measured with a Deltatrac II. In vitro we used a methanol miniburner incorporated into a doll, which could simulate low VO2(VCO2) and tidal breathing. In vivo we studied seven preterm infants < 1500 g. With the face mask VO2(VCO2) measurements were accurate at a flow of 3 L/min (error -1 +/- 0.8%), when tidal volume was < 15 mL/breath and the distance between mask and manikin < 1 cm. With hood and canopy VO2(VCO2) were underestimated at a flow of 3 L/min (error -13 +/- 1% and -14 +/- 5%), and results were markedly influenced by body position. For accurate measurements, the hood needed a flow of 4.5 L/min, the canopy 8.3 L/min. In vivo the face mask did not increase heart rate, respiration, activity, or rectal temperature, but hood and canopy increased rectal temperature by 0.3-0.4 degree C. For VO2(VCO2) measurements in infants < 1500 g, a face mask should be used, which is accurate at low flows and does not change body temperature. Accuracy at low flows and patient compatibility of breath sampling systems should be evaluated and reported for VO2(VCO2) measurements in preterm infants.

A cytochrome-b5-containing fusion protein similar to plant acyl lipid desaturases

The similarity between oleate and linoleate desaturase sequences from several plants was used to construct degenerate oligonucleotide primers for PCR experiments with cDNA transcribed from mRNA of ripening sunflower embryos. A DNA fragment was amplified and sequenced. Specific primers derived from this partial sequence were used for rapid amplification of the 3'- and 5'-ends of this cDNA. With appropriate primers derived from these sequences, a full-length clone of 1377 bp was amplified by PCR which, after sequencing, showed an open reading frame of 458 amino acids corresponding to a putative protein of about 52 kDa. Comparison with other desaturases showed the conserved three histidine boxes and the characteristic hydropathy profile of membrane-bound desaturases, but the amino acid identity was restricted to 18% and the N-terminal region was about 100 amino acids longer. This N-terminal extension showed high similarity with cytochrome b5 and, accordingly, the whole sequence can be considered as coding for a fusion protein between cytochrome b5 and a desaturase-like enzyme. Furthermore, we detected a similar cytochrome b5 fold in the previously sequenced delta 9 acyl-CoA desaturase from yeast, but in this enzyme it was located at the C-terminus. An alignment of these fusion proteins with other heme-binding proteins revealed desaturases to be novel members of the cytochrome b5 superfamily. A truncated DNA representing 366 bp of the 5'-end was amplified from the cDNA clone and expressed in Escherichia coli. The truncated cDNA coded for a soluble protein of about 12 kDa as shown by SDS/PAGE and N-terminal sequencing. The enriched recombinant protein exhibited redox absorbance spectra characteristic of plant microsomal cytochrome b5.

In vivo desaturation of cis-delta 9-monounsaturated to cis-delta 9,12-diunsaturated alkenylether glycerolipids

Plants convert lipid-bound cis-n-9 monoenoic to polyenoic fatty acid residues without involvement of corresponding CoA-thioesters. To provide additional evidence for this type of lipid-linked desaturation we incubated sn-1-O- and 2-O-(cis-9)octadecenylglycerol isomers with photoautotrophic cell cultures from tomato. After 14 days the fractions of phosphatidylcholine and monogalactosyldiacylglycerol were isolated and the incorporated glycerol ether backbones released by treatment with LiAlH4 (reduction of ester bonds) and short acid hydrolysis (cleavage of enol ether bonds). High performance liquid chromatography and mass spectroscopy of the products in appropriately derivatized form showed that the (cis-9)octadecenyl group in the sn-1 position of the phospholipid was nearly completely desaturated to a (cis-9,12)octadecadienyl residue having the same double bond arrangement as linoleic acid. In the galactolipid fraction the desaturation had progressed to octadecatrienyl residues. Similarly, the octadecenyl residue in the sn-2 position of the phospholipid was nearly completely desaturated to an octadecadienyl group. These results are unambiguous proof for lipid-linked desaturation by both microsomal and plastidial desaturase systems of plants.

Isomeric sn-1-octadecenyl and sn-2-octadecenyl analogues of lysophosphatidylcholine as substrates for acylation and desaturation by plant microsomal membranes

To provide supporting and independent evidence for lipid-linked desaturation of acyl groups in plant microsomal membranes, ether-analogous substrates were synthesized and used for in-vitro desaturation studies. The substrates included 1-O-(9-cis-octadecenyl)-sn-glycero-3-phosphocholine and 2-O-(9-cis-octadecenyl)-sn-glycero-3-phosphocholine as well as labelled 1-O-(9-cis-[9,10-3H2]octadecenyl)-sn-glycero-3-phosphocholine. In experiments with microsomal membranes from developing fruits of sunflower, it was shown that both isomeric alkenyl ether phospholipids were acylated with [14C]oleoyl-CoA and [14C]palmitoyl-CoA. In the presence of O2 and NADH, the oleoyl groups incorporated into both compounds, i.e. at the sn-1 and sn-2 positions of the glycerol backbone of the substrate, were desaturated to linoleoyl residues in similar proportions. Under the same conditions, an additional double bond, but not an enol-ether double bond, was introduced into the ether-linked side chain of acylated 1-O-(9-cis-[9,10-3H2]octadecenyl)-sn-glycero-3-phosphocholine. This represents the first demonstration of this type of desaturation with an alkenyl ether phospholipid and confirms previous conclusions that plants introduce second and further double bonds into lipid-linked acyl groups.