Xanthine dehydrogenase from the phototrophic purple bacterium Rhodobacter capsulatus is more similar to its eukaryotic counterparts than to prokaryotic molybdenum enzymes

Fourteen Rhodobacter capsulatus mutants unable to grow with xanthine as sole nitrogen source were isolated by random Tn5 mutagenesis. Five of these Tn5 insertions were mapped within two adjacent chromosomal EcoRI fragments hybridizing to oligonucleotides synthesized according to conserved amino acid sequences of eukaryotic xanthine dehydrogenases. DNA sequence analysis of this region revealed two open reading frames, designated xdhA and xdhB, encoding xanthine dehydrogenase. The deduced amino acid sequence of XDHA contains binding sites for two [2Fe-2S] clusters and FAD, whereas XDHB is predicted to contain the molybdopterin cofactor. In contrast to R. capsulatus, these three cofactor binding sites reside within a single polypeptide chain in eukaryotic xanthine dehydrogenases. The amino acid sequence of xanthine dehydrogenase from R. capsulatus showed a higher degree of similarity to eukaryotic xanthine dehydrogenases than to the xanthine dehydrogenase-related aldehyde oxidoreductase from Desulphovibrio gigas. The expression of an xdhA-lacZ fusion was induced when hypoxanthine or xanthine was added as sole nitrogen source. Mutations in nifR1 (ntrC) and nifR4 (rpoN, encoding sigma54) had no influence on xdh gene expression. A putative activator sensing the availability of substrate seems to respond to xanthine but not to hypoxanthine. The transcriptional start site of xdhA was mapped by primer extension analysis. Comparison with known promoter elements revealed no significant homology. Xanthine dehydrogenase from R. capsulatus was purified to homogeneity. The enzyme consists of two subunits with molecular masses of 85 kDa and 50 kDa respectively. N-terminal amino acid sequencing of both subunits confirmed the predicted start codons. The molecular mass of the native enzyme was determined to be 275 kDa, indicating an alpha2beta2-subunit structure. Analysis of the molybdenum cofactor of xanthine dehydrogenase from R. capsulatus revealed that it contains the molybdopterin cofactor and not a molybdopterin dinucleotide derivative.

Doppler color-flow imaging: screening of a patent foramen ovale in children scheduled for neurosurgery in the sitting position

A patent foramen ovale (PFO) is the most common cause of paradoxical air embolism during neurosurgical procedures in the posterior fossa in the sitting position in both adults and children. To detect right-to-left shunting, we performed Doppler color-flow imaging preoperatively in 30 children scheduled for neurosurgical procedures in the sitting position. A PFO was diagnosed on the basis of color alterations indicating an immediate blood shunt through a PFO. Six of 30 children (20%) had a PFO; in 4 of these children the sitting position then was avoided, and 2 children were operated on in a special supine position with minimal elevation of the head. Venous air embolism occurred in 9 of 24 (37%) children operated on in the sitting position and in none of the 6 children operated on in a nonsitting position. We conclude that Doppler color-flow mapping could be a useful noninvasive technique to screen children scheduled for neurosurgery in the sitting position for the presence of a PFO.

Quantification of the dermal vascular response to hyperbaric oxygen with laser-Doppler flowmetry

The vasoconstrictive response to hyperbaric oxygen (HBO2) therapy was non-invasively quantified in eight healthy volunteers at 1.95 and 2.5 atm abs (197.5 and 253.2 kPa; multiplace chamber, air environment) by laser-Doppler flowmetry (LDF). The sensors for continuous measurement of microvascular perfusion (flux) and skin temperature were localized on the thenar eminence. Transcutaneous oxygen (tcPO2) and carbon dioxide (tcPCO2) tensions, blood pressure, heart rate, respiration rate, peripheral oxygen saturation, and temperature of the hyperbaric chamber were recorded at five conditions: 1) baseline--air breathing at 1.0 atm abs, 2) after 15 min of HBO2 at 2.5 atm abs, 3) after 15 min of HBO2 at 1.95 atm abs, 4) 1 min after decompression with oxygen breathing at 1.0 atm abs, and 5) after 15 min of breathing air at 1.0 atm abs. Flux decreased continuously at conditions 2 (76.5%), 3 (50.6%), and 4 (37% of baseline, P < 0.05; Tukey test). Skin temperature fell below baseline at conditions 2, 3, 4 (P < 0.01, Tukey test), and 5 (P < 0.05, Tukey test, P < 0.001, analysis of variance). Range of correlation between inspired gas PO2 (PIO2) and alteration of flux 0.91 to 0.72, median -0.41. Correlation between PIO2 and tcPO2, r = 0.98. Chamber temperature and tcPCO2 remained stable. HBO2 reduced dermal microcirculation and temperature disproportionate to PIO2. LDF is suitable for use under hyperbaric conditions.

Laser doppler flowmetry in the hyperbaric environment

Continuous monitoring of laser Doppler (LD) flowmetry was performed in eight healthy volunteers (mean age 42.0 + 12.1 yr; range 25-62 yr) before, during and after hyperbaric oxygenation ([HBO at 2.5 and 1.95 ATA (atmosphere absolute)]).Two models of the discrimination analysis are presented which allow classification, resulting from the parameter obtained by the LD flowmetry.The results show that 100% separation of the LD data under HBO at 2.5 and 1.95 ATA including five parameters can be achieved with the first model. The second model for the analysis of four different phases with eight parameters still shows an obvious separation; however, only 75% of the group integration is correct. In addition to transcutaneous P(2) measurements, which are sometimes difficult to obtain perfectly, LD parameters will be of interest to manage HBO treatment, especially when peripheral circulation is reduced.

Pores formed by influenza hemagglutinin

Low pH-induced fusion mediated by the hemagglutinin (HA) of influenza virus involves a conformational change in the protein that leads to the insertion of a "fusion peptide" of the protein into the target membrane. It has been suggested that this insertion, aided by the formation of a complex of multiple HA trimers, would lead to perturbation of the bilayer structure of the membrane, initiating fusion. Here we present data showing that the interaction of the bromelain released ectodomain of the protein (BHA) with liposomal membranes at low pH leads to pore formation, at least at low temperatures. Strongly temperature-dependent low pH-induced inactivation of BHA resulted in a complete lack of activity of BHA above 10 degrees C. Even at 0 degrees C, only about 5% of the BHA participated in pore formation. Viral HA was less rapidly inactivated and still induced pores at 37 degrees C. BHA-induced pore formation showed a sigmoidal time course. Once BHA had formed a pore in one liposome, it did not form a pore in a further liposome. Quantitative analysis of pore formation indicated that one single BHA trimer sufficed to produce a pore. These data indicate that fusion peptide insertion perturbs the membrane and that the formation of a complex of trimers is not a prerequisite for the perturbation.

Molybdenum cofactor biosynthesis. The plant protein Cnx1 binds molybdopterin with high affinity

The molybdenum cofactor is an essential part of all eukaryotic molybdoenzymes. It is a molybdopterin (MPT) revealing the same core structure in all organisms. The plant protein Cnx1 from Arabidopsis thaliana is involved in the multi-step biosynthesis of molybdenum cofactor. Previous studies (Stallmeyer, B., Nerlich, A., Schiemann, J., Brinkmann, H., and Mendel, R. R. (1995) Plant J. 8, 751-762) suggested a function of Cnx1 in a late step of cofactor biosynthesis distal to the formation of MPT, i.e. conversion of MPT into molybdenum cofactor. Here we present the first biochemical evidences confirming this assumption. The protein Cnx1 consists of two domains (E and G) homologous to two distinct Escherichia coli proteins involved in cofactor synthesis. Binding studies with recombinantly expressed and purified Cnx1 and with its single domains revealed a high affinity of the G domain to MPT (kD = 0.1 microM) with equimolar binding. In contrast, the E domain of Cnx1 binds MPT with lower affinity (kD = 1.6 microM) and in a cooperative manner (nH = 1. 5). The entire Cnx1 showed a tight and cooperative MPT binding. Based on these data providing a common link between both domains that matches the previous characterization of plant and bacterial Cnx1 homologous mutants, we present a model for the function of Cnx1.

Drug induced double peak waveforms in the N20-component of somatosensory evoked potentials

The double peak waveform of the N20 component of the early somatosensory evoked potentials is a rare finding. In the present paper we investigated 9 patients (mean age +/- SD: 31.3 +/- 11.3 years; range 18-52 years) with the phenomenon of the two subcomponents of the primary cortical complex, after stimulation of the median nerve in a retrospective analysis. The results of the heterogenous patient group showed that the generation of the second subcomponent is not pathognomonic for patients with severe head injury, that it could be reversible and that pharmacological induced effects are presumably responsible for this phenomenon.

Brain-stem auditory evoked potential monitoring. The increase of the stimulus artifact in the development of brain death: a biological phenomenon?

Brain-stem auditory evoked potentials (BAEPs) were recorded in 12 dead subjects (mean age, 72.6 +/- 14.8 years), 30.6 +/- 19.5 hours (range 9-70) after abolished systemic circulation. Death was due to cardiac failure (n = 10), intracerebral hemorrhage (n = 1) and larynx cancer (n = 1). The presence and amplitude of the stimulus artifact were evaluated. The mean (+/- SD) amplitudes of the stimulus artifact was 0.03 +/- 0.02 microV on the left side and 0.01 +/- 0.02 microV on the right side. These findings in accordance with previous studies on comatose patients and brain dead subjects confirm that the increase of the stimulus artifact in the development of brain death, in spite of stimulation with alternating polarity, seems to reflect a biological phenomenon which is not found in dead subjects after complete cessation of systemic circulation.

[Computer-assisted detection of cerebral embolism using a multi-range principle]

Since its introduction into the clinical setting at the beginning of the 'eighties, transcranial Doppler sonography (TCD) has gained increasing acceptance as a non-invasive neuromonitoring technique. The ability of TCD to detect embolic particles within the cerebral blood vessels has been the subject of intensive investigation in recent years. In the present paper, a new method for the detection of emboli (multirange principle), intra-operatively during a neurosurgical intervention in a 35-year-old patient with a tumour in the posterior fossa and an open foramen ovale, is described for the first time. The method opens up new possibilities for the intra-operative management and the rapid assessment and diagnosis of paradoxical cerebral embolism.

Inflammatory reactions of the skin caused by adhesive EEG electrodes

The correct choice of electrodes for neurophysiologic monitoring is one of the unsolved problems in clinical practice and scientific research. In addition to the familiar electrodes, i.e., cup (silver-/silver-chloride, gold) and needle electrodes, adhesive electrodes (e.g., Zipprep electrodes) have been offered for rapid application and accurate signal recording. This case report indicates that adhesive electrodes can lead to superficial lesions of the skin or inflammatory infiltration.

Saisonale Variation von Deuterium und Sauerstoff-18 in Luftfeuchte und Niederschlag über Antarktika

Abstract D and (18)O distributions were investigated in Antarctic precipitation (falling snow) and in water vapour to study their dependance on season and sampling site. Long-term sampling at the former German Georg Forster Station during 1978-93 and at the Japanese Syowa Station during 1994-97 allow conclusions about the present seasonal isotopic variations in the water inflow to Antarctica. The δD and δ(18)O values of precipitation at these East Antarctic coastal stations were compared with corresponding data from the West Antarctic Georg von Neumayer and Halley stations. The monthly means of these long-term data sets show typical hysteresis-like seasonal patterns of isotopic composition. Significant time lags exist regarding station temperatures, while water vapour δD values do not show such hysteresis patterns. Here, half-yearly and even quarter-yearly time components were found by Fourier analysis. Attempts were made to describe the variation in δD and δ(18)O values of water vapour and precipitation as well as in the resulting deuterium excess by the mixed cloud isotopic model (MCIM) of Ciais and Jouzel.

The molecular area characteristics of the HIV-1 gp41-fusion peptide at the air/water interface. Effect of pH

The putative fusion peptide of HIV-1 is a highly surface active substance. Relevant measurements with the Langmuir monolayer technique have been carried out for a broad range of the pH in the aqueous subphase. The data are processed towards a quantitative analysis of the partitioning equilibrium between the interfacial and aqueous moieties. Our results reveal a pronounced decrease of the surface area per peptide molecule upon monolayer compression. This phenomenon could be interpreted in terms of an orientational transition experienced by an alpha-helical peptide structure. The area requirements at any fixed lateral pressure pass through a distinct minimum at a pH of 5.5 (+/-0.5). Such an apparent isoelectric point was confirmed by isoelectric focusing of peptide aggregates. Accordingly a drastic drop of the pK-values of the two basic amino acid residues in comparison with an aqueous medium is indicated. It can be readily explained based on an inherent decrease of the effective dielectric constant. The observed low pH in favor of an enhanced surface affinity of the peptide may be a significant factor concerning its function as a fusion promoting agent.

[Transcranial Doppler ultrasound--robotics-controlled transducers for quantifying the effect of acupuncture]

Transcranial Doppler Sonography (TCD) monitoring was carried out in 12 healthy subjects (mean age: 35.2 +/- 4.4 years; range: 26-41 years; 4 women, 8 men), prior to, during and following acupuncture. In all subjects an identical acupuncture scheme with a "general increase in Qi energy" setting was employed. Measurements were obtained with new robotic TCD probes enabling three-dimensional imaging of the middle cerebral artery by the use of the multi-scan technique. The results showed a significant (p < 0.01; ANOVA; Tukey test) increase in mean bloodflow velocity measured simultaneously at different depths within the right middle cerebral artery. Quantifiable changes in the physiological effects of acupuncture may contribute to improved acceptance of this unconventional complementary medical procedure.

Transcranial cerebral oximetry--is it clinically useless at this moment to interpret absolute values obtained by the INVOS 3100 cerebral oximeter?

Dynamic changes of regional cerebral oxygenation (rSO2) were measured simultaneously to laser Doppler flowmetry in a 35-year-old female during cerebral aneurysm surgery. In addition, to demonstrate the uselessness of the absolute values obtained by the INVOS 3100, cerebral oximeter readings from a pumpkin ("Styrian Cucurbita") are demonstrated. The results of the present study and of other reports discussed in this paper demonstrate that the INVOS 3100 cerebral oximeter should not be used at this moment as a measure reflecting absolute rSO2 values. However, it seems to be relevant that the INVOS 3100 system can monitor the dynamic changes in rSO2, although limitations have to be taken into consideration.

[Laser Doppler data analysis during interstitial laser thermotherapy with magnetic resonance control within the scope of an animal experiment study]

The aim of the present study was to investigate, using laser Doppler (LD) flowmetry, the phases immediately prior to and following experimental, neurosurgical laser therapy in animals. Two statistical models obtained on the basis of discriminant analysis are described. These models should enable the user to classify the sets of parameters calculated from the LD signals. With both models which contain 3 and 5 parameters, respectively. 100% discrimination of the two phases was attained. The usefulness of the models could be validated by results obtained with other models.

Transcranial cerebral oximetry in the hyperbaric environment

Continuous monitoring of dynamic changes of transcranial regional cerebral oxygenation (rSO2) was performed in 7 healthy volunteers (mean age 40.9 +/- 12.6 years; range 25-62 years) during normo- and hyperbaric oxygenation (HBO at 2.5 and at 1.95 ATA) using an INVOS 3100 cerebral oximeter. A significant change between HBO and control phase could be found in rSO2, alterations (p < 0.05; ANOVA, Tukey test). The results suggest that the calculation of rSO2 may be a useful method to monitor changes of oxygen saturation under hyperbaric conditions. However, the absolute quantification of rSO2 is useless at the moment and needs further investigation.

[Burst suppression detection in pEEG]

In the present paper, experience with the detection of burst suppression in the pEEG is described. The possibilities and limitations of the method during monitoring of anaesthesia under real conditions are discussed.

Abnormal brain stem auditory evoked potentials in a girl with the central alveolar hypoventilation syndrome

Brainstem auditory evoked potentials were recorded in a 3-year-old girl with the central alveolar hypoventilation syndrome (Ondine's syndrome). Abnormal findings were seen at the level of the mid to upper brain stem (wave III), which was not reproducibly recordable on the left side. This electrophysiologic abnormality is consistent with a previous finding in a patient with sleep apnea.

Preferential partitioning of melittin into the air/water interface: structural and thermodynamic implications

The membrane active agent melittin has been investigated with regard to the formation of a Langmuir monolayer and the accordingly induced surface activities. We show that in spite of its considerable solubility in an aqueous medium, this peptide nevertheless largely accumulates in the air/water interface unless the lateral pressure is raised beyond a certain threshold value depending on the pH in the subphase. The true surface concentrations have been determined by means of a recently developed novel method based on thermodynamic principles. It affords an access to the partitioning equilibrium between the surface and subphase domains, provided the latter surrounding is not excessively preferred. In the present case this approach was used to derive quantitative information on the pertinent interfacial structure and thermodynamics. In particular, the apparent molecular area and the Gibbs energy of mutual interaction in the monolayer could be evaluated as a function of the applied surface pressure. The data suggest the existence of two structural conversions in the course of an increasing lateral compression. The surface-associated peptide accordingly assumes three different states of successively reduced area requirements, supposedly owing to an orientational transition involving a straightening up of a helical conformation. This conclusion is corroborated by surface potential measurements reflecting corresponding changes of the effective dipole moment perpendicular to the surface.

Cerebral oximetry in dead subjects

Near-infrared spectroscopy is a technique used to monitor cerebral oxygenation. To validate the method, we measured regional oxygen saturation (rSo2) in the brains of 18 dead subjects (mean age, 74.4 +/- 14.6 years) 19.8 +/- 18.2 h (range, 1-73) after cessation of systemic circulation, and in 15 healthy probands (mean age, 34.2 +/- 8.7 years) with an INVOS 3100 cerebral oximeter. The mean (+/-SD) rSo2 in the dead subjects was 51.0 +/- 26.8% [range, 6-88%; left, 48.4 +/- 28.0% (n = 21); right, 54.4 +/- 25.7% (n = 16)]. The mean rSo2 in the control group was 68.4 +/- 5.2% (range, 60-76%; left, 68.1 +/- 5.0%; right, 68.7 +/- 5.6%). After removal of the brain at autopsy in five of the dead subjects, the rSo2 was 73.4 +/- 13.3% (15 measurements). Six of 18 of the dead subjects had values above the lowest values found in the healthy adults (> or = 60%). These findings raise concerns about the validity of cerebral rSo2 data in adults obtained by the INVOS 3100 system.

[Laser Doppler flowmetry--experiences from intensive care medicine]

Laser Doppler flowmetry makes it possible to determine the status of the microcirculation with the aid of a non-invasive procedure. The present article describes the use in two ICU patients of Doppler laser flowmetry to effect a qualitative and quantitative evaluation of the side effects that may occur when using various stimulation procedures.