Morphological Diversity and Evolution of Jaw Morphologies in Zeiform Fishes (Teleostei, Paracanthopterygii).

Zeiformes (dories, tinselfishes, and oreos) are primarily benthopelagic acanthomorph fishes, distributed between 50 and 1000 m depth on continental slopes and on flanks of oceanic islands and seamounts. Among the interesting morphological adaptations of zeiform fishes are their unique and highly protrusible jaws involving premaxillae with long ascending processes and a four-bar linkage, including mobile palatines that pivot on their posterior articulation. This adaptation for increased jaw protrusion has enabled zeiform fishes to capture elusive prey more efficiently and is arguably a major factor in their morphological diversity and evolutionary success. This study examines the evolution of zeiform jaw morphologies using 3D landmark-based multivariate morphometrics as well as phylomorphospace analysis. Results show that the descendants of the zeiform ancestor branched rapidly early in their history, retaining conservative jaw morphologies during this early branching, but subsequently strongly diverged in many of the resulting lineages. Results from this study are compared with earlier research based on overall body form, demonstrating that morphological variation within Zeiformes arose along at least two distinct trajectories: body form and jaw morphology. Variation among genera in body form is not associated with variation among the same genera in jaw morphology, and vice versa. Hypotheses to explain the apparent decoupling of body shape and jaw morphology are addressed along with avenues for further study to better understand the morphological evolution of these iconic fishes.

Les Zéiformes (e.g., dorés, oréos et poissons scintillants) sont des poissons benthopélagiques du groupe des Acanthomorpha trouvés entre 50 et 1000m de profondeurs sur les talus continentaux, et sur les abords des iles océaniques et des monts sous-marins. Parmi les adaptations morphologiques des zéiformes figurent leur mâchoires protrusibles, composées de prémaxillaires avec de longs processus ascendants et un mécanisme à quatre barres qui implique des os palatins mobiles qui pivotent autour de leur articulation postérieure. Ces adaptations morphologiques conduisent à une protrusion buccale sur de plus grandes distances et plus efficace, permettant aux zéiformes de capturer des proies autrement insaisissables et sont des éléments majeurs de la diversité morphologique du groupe ainsi que de leur succès évolutif. Cette étude examine l'évolution de la morphologie des mâchoires des zéiformes via des mesures de morphométrie géométrique 3D par points d'intérêts et des analyses d'espace phylo-morphologique. Les résultats montrent que les Zéiformes se sont rapidement séparés du plus vieil ancêtre commun mais ont initialement conservés des morphologies de mâchoires similaires. Suite à cette séparation initiale, les morphologies ont rapidement divergé menant à la diversité courante du groupe. Une comparaison des résultats obtenus ici avec des études précédentes sur la forme du corps des Zéiformes soutient que l'évolution morphologique du groupe a suivi au moins deux axes distincts : la forme du corps et la morphologie des mâchoires. Les différences de formes du corps entre genres ne sont pas corrélées avec les différences de formes de mâchoires entre ces mêmes genres, ni réciproquement. Des hypothèses quant au découplage entre la forme du corps et la morphologie des mâchoires sont avancées et plusieurs pistes de recherche future pour nous permettre de mieux comprendre l'évolution morphologique de ce groupe de poissons fascinant sont proposées.

Los zeiformes (dorios, peces oropel y oreos) son peces acantomorfos principalmente bentopelágicos, los cuales se encuentran distribuidos entre 50 y 1000 m de profundidad en los taludes continentales, así como en los flancos de islas oceánicas y montes submarinos. Estos peces poseen adaptaciones morfológicas particulares, entre las cuales se incluye la presencia de una mandíbula altamente protusible incluyendo premaxilares con procesos ascendentes largos, y una articulación de 4-barras con palatinos móviles que pivotean sobre su articulación posterior. Esta adaptación en la protrusión mandibular ha permitido a los zeiformes capturar presas elusivas de manera más eficiente, y posiblemente ha sido un factor importante en su diversidad morfológica y éxito evolutivo. El presente estudio examina la evolución de la morfología de la mandíbula de los peces zeiformes utilizando un análisis morfométrico multivariado basado en puntos de referencia (3D landmark-based), así como un análisis de tipo filomorfoespacial. Los resultados de este trabajo muestran que los zeiformes se diversificaron rápidamente en su historia temprana, manteniendo la morfología de la mandíbula inicial durante esta etapa. No obstante, posteriormente este grupo de peces se diversificaron considerablemente en diferentes linajes. Asimismo, los resultados obtenidos se compararon con investigaciones anteriores basadas en la forma general del cuerpo, lo que demuestra que la variación morfológica de los zeiformes surgió a lo largo de al menos dos rasgos morfológicos distintos: la forma del cuerpo y la morfología de la mandíbula. Con relación a esto, se encontró que la variación de la forma del cuerpo no está asociada con la variación de la morfología de la mandíbula entre los mismos géneros de los peces zeifomes, y viceversa. Finalmente, este estudio aborda las hipótesis que explican la aparente disociación entre la forma del cuerpo y la morfología de la mandíbula de este grupo de peces, así como las rutas para estudios posteriores que ayude a comprender mejor la evolución morfológica de estos icónicos peces.

Physician Assistants and Nurse Practitioners in Primary Care Plus: A Systematic Review.

INTRODUCTION: Shifting specialist care from the hospital to primary care/community care (also called primary care plus) is proposed as one option to reduce the increasing healthcare costs, improve quality of care and accessibility. The aim of this systematic review was to get insight in primary care plus provided by physician assistants or nurse practitioners. METHODS: Scientific databases and reference list were searched. Hits were screened on title/abstract and full text. Studies published between 1990-2018 with any study design were included. Risk of bias assessment was performed using QualSyst tool. RESULTS: Search resulted in 5.848 hits, 15 studies were included. Studies investigated nurse practitioners only. Primary care plus was at least equally effective as hospital care (patient-related outcomes). The number of admission/referral rates was significantly reduced in favor of primary care plus. Barriers to implement primary care plus included obtaining equipment, structural funding, direct access to patient-data. Facilitators included multidisciplinary collaboration, medical specialist support, protocols. CONCLUSIONS AND DISCUSSION: Quality of care within primary care plus delivered by nurse practitioners appears to be guaranteed, at patient-level and professional-level, with better access to healthcare and fewer referrals to hospital. Most studies were of restricted methodological quality. Findings should be interpreted with caution.

Universal free-energy landscape produces efficient and reversible electron bifurcation.

For decades, it was unknown how electron-bifurcating systems in nature prevented energy-wasting short-circuiting reactions that have large driving forces, so synthetic electron-bifurcating molecular machines could not be designed and built. The underpinning free-energy landscapes for electron bifurcation were also enigmatic. We predict that a simple and universal free-energy landscape enables electron bifurcation, and we show that it enables high-efficiency bifurcation with limited short-circuiting (the EB scheme). The landscape relies on steep free-energy slopes in the two redox branches to insulate against short-circuiting using an electron occupancy blockade effect, without relying on nuanced changes in the microscopic rate constants for the short-circuiting reactions. The EB scheme thus unifies a body of observations on biological catalysis and energy conversion, and the scheme provides a blueprint to guide future campaigns to establish synthetic electron bifurcation machines.

The effect of postoperative closed incision negative pressure therapy on the incidence of donor site wound dehiscence in breast reconstruction patients: DEhiscence PREvention Study (DEPRES), pilot randomized controlled trial.

AIM: Wound dehiscence is a serious postoperative complication associated both with high morbidity and mortality. It has a significant rate of occurrence in breast reconstruction surgeries with a deep internal epigastric perforator (DIEP) and with a profunda artery perforator (PAP) flap. Risk factors for wound dehiscence include smoking, diabetes mellitus, chronic obstructive pulmonary disease, and obesity. The aim of this pilot study was to assess whether postoperative treatment with closed incision negative pressure therapy (ciNPT) decreases the incidence of donor site wound dehiscence in breast reconstruction patients. METHOD: Women undergoing a breast reconstruction with a DIEP or PAP flap were enrolled in a pilot randomized controlled trial and assigned treatment with either ciNPT or adhesive strips. The primary outcome was wound dehiscence upon follow-up after four weeks. Secondary outcomes that were evaluated included wound infection, pain, and allergy. There was no loss to follow-up. RESULTS: This pilot study included 51 women (n = 25 ciNPT, n = 26 adhesive strips). The two groups did not differ significantly in patients demographics or comorbidities. Wound dehiscence occurred in 11 patients (n = 2 ciNPT, n = 9 adhesive strips). This difference was statistically significant: p = 0.038. There were no statistically significant differences in secondary outcomes between the two groups. CONCLUSION: In this pilot study, postoperative treatment with ciNPT decreased the incidence of donor site wound dehiscence in breast reconstruction patients. Further research is ongoing by the same hospital. This trial was registered in the Netherlands Trial Register (NTR) under ID no. NTR5808.

Standard and individually determined thermal pain stimuli induce similar brain activations.

BACKGROUND: Several functional magnetic resonance imaging (fMRI) studies use thermal pain stimuli to determine brain activation patterns during pain. Studies use either a standard temperature condition for all participants or an individualized temperature condition based on the individually determined pain threshold of the participant. The aim of the present study was to compare both conditions in the same participants. METHODS: Eighteen healthy participants (21-29 years) underwent four fMRI runs, in each of which they received three types of thermal stimuli: neutral (32 °C), warm (37 °C) and painfully hot. In two runs, the painfully hot stimulus was set at a standard temperature of 46 °C; in the other two runs, the temperature was set at the subject's individual pain threshold (46-48 °C). fMRI (blood oxygen level dependent) was performed on a 1.5 T MR scanner (GE Signa). Pre-processing and statistical analyses were performed using Statistical Parametric Mapping (SPM8) software. RESULTS: While the stimulation temperatures were lower in the standard temperature condition, both conditions activated the same brain regions. When comparing the conditions directly to each other, we did not find significantly different grey matter activation patterns. CONCLUSIONS: The similar activation patterns between the two conditions suggest that it is not necessary to use individualized stimuli per se. The temperature of 46 °C appeared to be an adequate temperature for standardized stimulation to observe significant brain activations related to thermal pain.

Environmental constraints defining the distribution, composition, and evolution of chlorophototrophs in thermal features of Yellowstone National Park.

Chlorophotoautotrophy, the use of chlorophylls to convert light energy into chemical energy for carbon dioxide fixation, is the primary metabolic process linking the inorganic and organic carbon pools on Earth. To understand the potential effects of various environmental constraints on the evolution of chlorophototrophy better, we studied the distribution, diversity, and abundance of chlorophylls and genes involved in their synthesis along geothermal gradients in Yellowstone National Park, Wyoming. Genes involved in chlorophyll biosynthesis were constrained to temperatures of less than ~70 °C and were only detected at this elevated temperature when the pH was in the circumneutral to alkaline range. The upper temperature limit for the detection of chlL/bchL(1) and bchY(2) decreased systematically with increasingly acidic pH, an observation likely attributable to sulfide, which upon oxidation, generates acidic spring water and reduces the availability of bicarbonate the preferred source of inorganic carbon for phototrophs. Spring pH was also the best predictor of the phylogenetic diversity of chlL/bchL communities. The phylogenetic similarity of chlL/bchL genes between sites was significantly correlated with that of chlorophylls. The predominance of chlorophyll a and bacteriochlorophyll a among extracted pigments was consistent with predominance of chlL/bchL genes affiliated with the Cyanobacteria and Chloroflexiales, respectively, and might be related to the fact that the majority of these organisms are photoautotrophs. Together, these results suggest that a combination of temperature, pH, and/or sulfide influences the distribution, diversity, and evolution of chlorophotrophs and the chlorophylls that they synthesize.

A late methanogen origin for molybdenum-dependent nitrogenase.

Mounting evidence indicates the presence of a near complete biological nitrogen cycle in redox-stratified oceans during the late Archean to early Proterozoic (c. 2.5-2.0 Ga). It has been suggested that the iron (Fe)- or vanadium (V)-dependent nitrogenase rather than molybdenum (Mo)-dependent form was responsible for dinitrogen fixation during this time because oceans were depleted in Mo and rich in Fe. We evaluated this hypothesis by examining the phylogenetic relationships of proteins that are required for the biosynthesis of the active site cofactor of Mo-nitrogenase in relation to structural proteins required for Fe-, V- and Mo-nitrogenase. The results are highly suggestive that among extant nitrogen-fixing organisms for which genomic information exists, Mo-nitrogenase is unlikely to have been associated with the Last Universal Common Ancestor. Rather, the origin of Mo-nitrogenase can be traced to an ancestor of the anaerobic and hydrogenotrophic methanogens with acquisition in the bacterial domain via lateral gene transfer involving an anaerobic member of the Firmicutes. A comparison of substitution rates estimated for proteins required for the biosynthesis of the nitrogenase active site cofactor and for a set of paralogous proteins required for the biosynthesis of bacteriochlorophyll suggests that Nif emerged from a nitrogenase-like ancestor approximately 1.5-2.2 Ga. An origin and ensuing proliferation of Mo-nitrogenase under anoxic conditions would likely have occurred in an environment where anaerobic methanogens and Firmicutes coexisted and where Mo was at least episodically available, such as in a redox-stratified Proterozoic ocean basin.

[Prevalence of dental disorders in 483 horses and ponies]. / De prevalentie van gebitsafwijkingen bij 483 paarden en pony's.

Prevalence of dental disorders in 483 horses and ponies Five equine veterinarians working at three equine referral hospitals examined the oral cavity of 483 horses and ponies prior to surgery, to gain information about the prevalence of common dental disorders in the horse. A thorough examination, using hands/fingers, a full-mouth speculum, a dental mirror and a good light source, is essential to detect such disorders. Many horses examined needed dental attention even though there were no problems with mastication or riding. The most detected abnormalities were sharp enamel points on the buccal side of the upper arcade and the lingual side of the lower arcade, and hooks at 106/206 and 311/411. Regular dental care would improve the condition and welfare of horses.

Rectal acetaminophen does not reduce morphine consumption after major surgery in young infants.

BACKGROUND: The safety and value of acetaminophen (paracetamol) in addition to continuous morphine infusion has never been studied in newborns and young infants. We investigated the addition of acetaminophen to evaluate whether it decreased morphine consumption in this age group after major thoracic (non-cardiac) or abdominal surgery. METHODS: A randomized controlled trial was performed in 71 patients given either acetaminophen 90-100 mg kg(-1) day(-1)or placebo rectally, in addition to a morphine loading dose of 100 microg kg(-1) and 5-10 microg kg(-1) h(-1) continuous infusion. Analgesic efficacy was assessed using Visual Analogue Scale (VAS) and COMFORT scores. Extra morphine was administered if VAS was > or = 4. RESULTS: We analysed data of 54 patients, of whom 29 received acetaminophen and 25 received placebo. Median (25-75th percentile) age was 0 (0-2) months. Additional morphine bolus requirements and increases in continuous morphine infusion were similar in both groups (P = 0.366 and P = 0.06, respectively). There was no significant difference in total morphine consumption, respectively, 7.91 (6.59-14.02) and 7.19 (5.45-12.06) mug kg(-1) h(-1) for the acetaminophen and placebo group (P = 0.60). COMFORT [median (25-75th percentile) acetaminophen 10 (9-12) and placebo 11 (9-13)] and VAS [median (25-75th percentile) acetaminophen 0.0 (0.0-0.2) and placebo 0.0 (0.0-0.3)] scores did not differ between acetaminophen and placebo group (P = 0.06 and P = 0.73, respectively). CONCLUSIONS: Acetaminophen, as an adjuvant to continuous morphine infusion, does not have an additional analgesic effect and should not be considered as standard of care in young infants, 0-2 months of age, after major thoracic (non-cardiac) or abdominal surgery.

Pain assessment in profound cognitive impaired children using the Checklist Pain Behavior; is item reduction valid?

There are both commonalities and idiosyncratic features in the reaction of pain children with profound cognitive impairment (CI), and that there is no evidence to suggest that idiosyncratic behavior is more characteristic of this population than of any other population. The main objective of this study was to identify whether the 23-item version of the Checklist Pain Behavior could be reduced to 10 items. Previous research demonstrated that only these 10 items discriminated between absence and presence of pain. Second, we wanted to explore the underlying structure of these 10 selected items including its performance. Data of 477 observations in 73 children were used. All these children were video-taped while they were admitted to the Sophia Children's Hospital for surgery, twice before and five times after surgery. These video-tapes were scored by an independent observer. A visual analogue scale (VAS) by a researcher was used to assess the presence of pain. We tested whether the underlying structure was unidimensional, and whether it had differential qualities between pain and no pain, and to which degree. Using a modern psychometric method, i.e., Mokken scaling model, we unraveled the interdependency of the pain response in CI-children, in that the structure turned out to be unidimensional. In addition, these behaviors could be hierarchically ordered in terms of frequency of occurrences. Finally, these behaviors had to a high degree the potentialities to estimate the likelihood of occurrence of pain.

Biomimetic synthesis of a H2 catalyst using a protein cage architecture.

A biomimetic approach has been used to develop an artificial hydrogenase that catalyses the efficient reduction of protons producing hydrogen gas. Analogous to the unique biological metal clusters found in hydrogenase enzymes, the engineered active sites are small, well-defined Pt clusters deposited on the interior of a heat shock protein cage architecture with stoichiometries of 150 to 1000 Pt per protein cage. The proton reduction reaction is driven by visible light through a coupled reaction with Ru(bpy)3(2+) and methyl viologen as an electron-transfer mediator. Hydrogen production rates are comparable to those of hydrogenase on a per protein basis and exceed production rates of other reported Pt-based catalysts. These results demonstrate the utility of a biomimetic approach toward addressing the needs of hydrogen production.

[Rectal tears in the horse: malpractice or an unfortunate accident?]. / Rectumscheuren bij het paard: beroepsfout ofeen ongelukkig toeval?

Rectal tears are a relatively rare complication of rectal palpation, mating or dystocia, and idiopathic spontaneous occurrence of rectal perforation has also been described. Rectal tears have been classified in a three or a four-grade system. Immediate recognition of the fact that a tear has been made and prompt action will improve the horses chance of survival, and is the best defence of the veterinarian against legislation. There is no clear explanation why rectal tears sometimes occur. A questionnaire of the Netherlands Equine Veterinary Association revealed that rectal tears occurred both to inexperienced veterinarians and to very experienced colleagues, working with or without a probe for ultrasonography. In the opinion of the authors, the approach in the legislation of rectal tears should be that a rectal tear is only considered 'malpractice' if the veterinarian obviously acted carelessly. However, this would create the ridiculous situation that it seems better for the veterinarian-client relationship when the veterinarian confesses to 'careless' rectal palpation. This point needs further clarification, and perhaps an 'insurance of the horse for rectal palpation' will be the solution. Further, retrospectively over the last ten years, the problem is often not 'making a rectal tear', but 'lacking recognition of making a tear'. Whenever a rectal tear is suspected, the veterinarian must assess its severity, discuss the problem openly with the owner and apply appropriate treatment including referral.

Mechanistic features and structure of the nitrogenase alpha-Gln195 MoFe protein.

EPR signals observed under CO and C(2)H(2) during nitrogenase turnover were investigated for the alpha-Gln(195) MoFe protein, an altered form for which the alpha-His(195) residue has been substituted by glutamine. Under CO, samples show S = 1/2 hi- and lo-CO EPR signals identical to those recognized for the wild-type protein, whereas the S = 3/2 signals generated under high CO/high flux conditions differ. Previous work has revealed that the EPR spectrum generated under C(2)H(2) exhibits a signal (S(EPR1)) originating from the FeMo-cofactor having two or more bound C(2)H(2) adducts and a second signal (S(EPR2)) arising from a radical species [Sørlie, M., Christiansen, J., Dean, D. R., and Hales, B. J. (1999) J. Am. Chem. Soc. 121, 9457-9458]. Pressure-dependent studies show that the intensity of these signals has a sigmoidal dependency at low pressures and maximized at 0.1 atm C(2)H(2) with a subsequent decrease in steady-state intensity at higher pressures. Analogous signals are not recognized for the wild-type MoFe protein. Analysis of the principal g-factors of S(EPR2) suggests that it either represents an unusual metal cluster or is a carboxylate centered radical possibly originating from homocitrate. Both S(EPR1) and S(EPR2) exhibit similar relaxation properties that are atypical for S = 1/2 signals originating from Fe-S clusters or radicals and indicate a coupled relaxation pathway. The alpha-Gln(195) MoFe protein also exhibits these signals when incubated under turnover conditions in the presence of C(2)H(4). Under these conditions, additional inflections in the g 4-6 region assigned to ground-state transitions of an S = 3/2 spin system are also recognized and assigned to turnover states of the MoFe protein without C(2)H(4) bound. The structure of alpha-Gln(195) was crystallographically determined and found to be virtually identical to that of the wild-type MoFe protein except for replacement of an NuH-S hydrogen bond interaction between FeMo-cofactor and the imidazole side chain of alpha-His(195) by an analogous interaction involving Gln.

MgATP-Bound and nucleotide-free structures of a nitrogenase protein complex between the Leu 127 Delta-Fe-protein and the MoFe-protein.

A mutant form of the nitrogenase iron protein with a deletion of residue Leu 127, located in the switch II region of the nucleotide binding site, forms a tight, inactive complex with the nitrogenase molybdenum iron (MoFe) protein in the absence of nucleotide. The structure of this complex generated with proteins from Azotobacter vinelandii (designated the L127Delta-Av2-Av1 complex) has been crystallographically determined in the absence of nucleotide at 2.2 A resolution and with bound MgATP (introduced by soaking) at 3.0 A resolution. As observed in the structure of the complex between the wild-type A. vinelandii nitrogenase proteins stabilized with ADP.AlF(4-), the most significant conformational changes in the L127Delta complex occur in the Fe-protein component. While the interactions at the interface between the MoFe-protein and Fe-proteins are conserved in the two complexes, significant differences are evident at the subunit-subunit interface of the dimeric Fe-proteins, with the L127Delta-Av2 structure having a more open conformation than the wild-type Av2 in the complex stabilized by ADP.AlF(4-). Addition of MgATP to the L127Delta-Av2-Av1 complex results in a further increase in the separation between Fe-protein subunits so that the structure more closely resembles that of the wild-type, nucleotide-free, uncomplexed Fe-protein, rather than the Fe-protein conformation in the ADP.AlF(4-) complex. The L127Delta mutation precludes key interactions between the Fe-protein and nucleotide, especially, but not exclusively, in the region corresponding to the switch II region of G-proteins, where the deletion constrains Gly 128 and Asp 129 from forming hydrogen bonds to the gamma-phosphate and activating water for attack on this group, respectively. These alterations account for the inability of this mutant to support mechanistically productive ATP hydrolysis. The ability of the L127Delta-Av2-Av1 complex to bind MgATP demonstrates that dissociation of the nitrogenase complex is not required for nucleotide binding.

Insights into nucleotide signal transduction in nitrogenase: structure of an iron protein with MgADP bound.

Coupling the energy of nucleoside triphosphate binding and hydrolysis to conformational changes is a common mechanism for a number of proteins with disparate cellular functions, including those involved in DNA replication, protein synthesis, and cell differentiation. Unique to this class of proteins is the dimeric Fe protein component of nitrogenase in which the binding and hydrolysis of MgATP controls intermolecular electron transfer and reduction of nitrogen to ammonia. In the work presented here, the MgADP-bound (or "off") conformational state of the nitrogenase Fe protein has been captured and a 2.15 A resolution X-ray crystal structure is presented. The structure described herein reveals likely mechanisms for long-range communication from the nucleotide-binding sites for controlling the affinity of association with the MoFe protein component. Two pathways, termed switches I and II, appear to be integral to this nucleotide signal transduction mechanism. In addition, the structure provides the basis for the changes in the biophysical properties of the [4Fe-4S] cluster observed when Fe protein binds nucleotides. The structure of the MgADP-bound Fe protein provides important insights into the respective contributions of nucleotide interaction and complex formation in defining the conformational states that are the keys to nitrogenase catalysis.

Experimental validation of a new coronary guide wire labeled with rubidium 81/krypton 81m for continuous assessment of myocardial blood flow.

BACKGROUND: The rubidium 81/krypton 81m method was suggested for assessment of myocardial blood flow (MBF) three decades ago. This study investigates the novel concept of using 81Rb-/81mKr-labeled coronary guide wires with wire-attached 81Rb activity and diffusable 81mKr gas for assessment of lesion-specific impairment of MBF by evaluation of the 81Rb/81mKr activity ratio. The feasibility of wire production is tested, and application of the method is investigated in the canine model. METHODS AND RESULTS: Conventional coronary guide wires for angioplasty (0.014 in) were labeled with radioactive 81Rb/81mKr by ion bombardment of the wire tip. A total of 16 of the 18 wires labeled in series showed successful 81Rb fixation in combination with free 81mKr gas diffusability during quality control measurements. The suitability of the wires to assess MBF in combination with an external gamma ray detector was investigated in open-chested dogs. Electromagnetic measurement of coronary blood flow (CBF) was used as reference, providing a signal that is directly linked to volumetric MBF. The 81Rb/81mKr ratio tracked changes in CBF reliably in all 6 dogs. The found linear dependence of measured 81Rb/81mKr count rates on measured CBF supports the modeling assumptions made to apply the theoretic basis of the 81Rb/81mKr technique to 81Rb-labeled coronary guide wires. CONCLUSION: 81Rb-/81mKr-labeled coronary guide wires provide a signal that indicates volumetric MBF directly. This unique capability may qualify the technique as a valuable tool for research purposes and as an attractive method for invasive cardiology at centers where the logistic arrangements for short-lived isotope supply are provided.

Reversible carbon monoxide binding and inhibition at the active site of the Fe-only hydrogenase.

Carbon monoxide binding and inhibition have been investigated by electron paramagnetic resonance (EPR) spectroscopy in solution and in crystals of structurally described states of the Fe-only hydrogenase (CpI) from Clostridium pasteurianum. Simulation of the EPR spectrum of the as-isolated state indicates that the main component of the EPR spectrum consists of the oxidized state of the "H cluster" and components due to reduced accessory FeS clusters. Addition of carbon monoxide to CpI in the presence of dithionite results in the inhibition of hydrogen evolution activity, and a characteristic axial EPR signal [g(eff(1)), g(eff(2)), and g(eff(3)) = 2.0725, 2.0061, and 2.0061, respectively] was observed. Hydrogen evolution activity was restored by successive sparging with hydrogen and argon and resulted in samples that exhibited the native oxidized EPR signature that could be converted to the reduced form upon addition of sodium dithionite and hydrogen. To examine the relationship between the spectroscopically defined states of CpI and those observed structurally by X-ray crystallography, we have examined the CpI crystals using EPR spectroscopy. EPR spectra of the crystals in the CO-bound state exhibit the previously described axial signal associated with CO binding. The results indicate that the addition of carbon monoxide to CpI results in a single reversible carbon monoxide-bound species characterized by loss of enzyme activity and the distinctive axial EPR signal.

A novel FeS cluster in Fe-only hydrogenases.

Many microorganisms can use molecular hydrogen as a source of electrons or generate it by reducing protons. These reactions are catalysed by metalloenzymes of two types: NiFe and Fe-only hydrogenases. Here, we review recent structural results concerning the latter, putting special emphasis on the characteristics of the active site.

Modulating the midpoint potential of the [4Fe-4S] cluster of the nitrogenase Fe protein.

Protein-bound [FeS] clusters function widely in biological electron-transfer reactions, where their midpoint potentials control both the kinetics and thermodynamics of these reactions. The polarity of the protein environment around [FeS] clusters appears to contribute largely to modulating their midpoint potentials, with local protein dipoles and water dipoles largely defining the polarity. The function of the [4Fe-4S] cluster containing Fe protein in nitrogenase catalysis is, at least in part, to serve as the nucleotide-dependent electron donor to the MoFe protein which contains the sites for substrate binding and reduction. The ability of the Fe protein to function in this manner is dependent on its ability to adopt the appropriate conformation for productive interaction with the MoFe protein and on its ability to change redox potentials to provide the driving force required for electron transfer. Phenylalanine at position 135 is located near the [4Fe-4S] cluster of nitrogenase Fe protein and has been suggested by amino acid substitution studies to participate in defining both the midpoint potential and the nucleotide-induced changes in the [4Fe-4S] cluster. In the present study, the crystal structure of the Azotobacter vinelandii nitrogenase Fe protein variant having phenylalanine at position 135 substituted by tryptophan has been determined by X-ray diffraction methods and refined to 2.4 A resolution. A comparison of available Fe protein structures not only provides a structural basis for the more positive midpoint potential observed in the tryptophan substituted variant but also suggests a possible general mechanism by which the midpoint potential could be controlled by nucleotide interactions and nitrogenase complex formation.

Structure and mechanism of iron-only hydrogenases.

The recent elucidation of the structures of iron-only hydrogenases from the microorganisms Clostridium pasteurianum and Desulfovibrio desulfuricans has revealed that the presumed site of reversible hydrogen oxidation exists as a unique, protein-associated organometallic prosthetic group. Details of the hydrogenase structures provide insight into the chemical mechanism of this highly evolved catalyst.