Spectral manifestation of optical Tamm states in a metal-cholesteric liquid crystals stack

The reflection spectrum of linearly polarized light by a system consisting of a metal film and two adjacent sequentially located cholesteric liquid crystals (CLCs) with opposite helical twists is theoretically studied. The system contains a dielectric index-matching layer (DIML) between the metal film and the CLC layers. It is shown that in such a system the excitation of optical Tamm states (OTSs) by linearly polarized light is possible. The influence of the CLC pitch, refractive indices, and thicknesses of the DIML and metal film on the OTS manifestation in the reflection spectrum of the system is studied. The strong influence of the DIML thickness on the OTS wavelength and the appearance of multiple OTSs with an increase in the DIML thickness is noted.

Charge trapping by iodine ions in photorefractive Sn2P2S6 crystals

Electron paramagnetic resonance (EPR) is used to establish the role of iodine as an electron trap in tin hypothiodiphosphate (Sn₂P₂S₆) crystals. Iodine ions are unintentionally incorporated when the crystals are grown by the chemical-vapor-transport method with SnI₄ as the transport agent. The Sn₂P₂S₆ crystals consist of Sn²⁺ ions and (P₂S₆)^4- anionic groups. During growth, an iodine ion replaces a phosphorus in a few of the anionic groups, thus forming (IPS₆)^4- molecular ions. Following an exposure at low temperature to 633 nm laser light, these (IPS₆)^4- ions trap an electron and convert to EPR-active (IPS₆)^5- groups with S = 1/2. A concentration near 1.1 × 10¹⁷ cm^-3 is produced. The EPR spectrum from the (IPS₆)^5- ions has well-resolved structure resulting from large hyperfine interactions with the ¹²⁷I and ³¹P nuclei. Analysis of the angular dependence of the spectrum gives principal values of 1.9795, 2.0123, and 2.0581 for the g matrix, 232 MHz, 263 MHz, and 663 MHz for the ¹²⁷I hyperfine matrix, and 1507 MHz, 1803 MHz, and 1997 MHz for the ³¹P hyperfine matrix. Results from quantum-chemistry modeling (unrestricted Hartree-Fock/second-order Møller-Plesset perturbation theory) support the (IPS₆)^5- assignment for the EPR spectrum. The transient two-beam coupling gain can be improved in these photorefractive Sn₂P₂S₆ crystals by better controlling the point defects that trap charge.

Spectrally tunable chiral Bragg reflectors for on-demand beam generation

We demonstrate the generation of spectrally tunable phase-dependent wavefronts, using the 2D Airy as the primary test case, via a polymer-stabilized cholesteric liquid crystal (PSCLC) element. Specifically, we use a novel spatial light modulator (SLM) based projection system to photo-align the initial helix angle landscape of the PSCLC so that it imparts the appropriate cubic phase profile to the reflected beam. This element is spectrally selective, with a reflection bandwidth of ≈ 100 nm, and electrically tunable from λ = 530 nm to 760 nm. Under both green and red laser illumination, the element is shown to conditionally form an Airy beam depending on the position of the electrically tailored reflection band. We briefly demonstrate the generality of this approach by producing PSCLC elements which form a computer-generated hologram and a higher-order Mathieu beam.

A Pasteurised Concentrate of Human Plasma Factor XIII for Therapeutic Use

A therapeutic concentrate of factor XIII containing both A and B sub-units has been prepared from 300 kg pools of human plasma. The process starts from a cold-ethanol fraction from cryoprecipitate supernatant and therefore does not interfere with the recovery of other clinically valuable plasma proteins. Factor XIII is purified approximately 600-fold from plasma by precipitation with sodium citrate and by the removal of fibrinogen by brief heating. The product has been pasteurised in sorbitol solution to inactivate blood-borne viruses, ultrafiltered to remove sorbitol, adsorbed with bentonite and freeze-dried in a formulation meeting requirements for intravenous injection.

Flexoelectro-optic effect and two-beam energy exchange in a hybrid photorefractive cholesteric cell with a short-pitch horizontal helix

We develop a theoretical model to describe two-beam energy exchange in a hybrid photorefractive cholesteric cell with a short-pitch helix oriented parallel to the cell substrates (so-called uniformly lying helix configuration). Weak and strong light beams incident on the hybrid cell interfere and induce a periodic space-charge field in the photorefractive substrate of the cell, which penetrates into the cholesteric liquid crystal (LC). Due to the flexoelectro-optic effect an interaction of the photorefractive field with the LC flexopolarization causes the spatially periodic modulation of the helix axis in the plane parallel to the cell substrates. Coupling of a weak signal beam with a strong pump beam at the LC permittivity grating, induced by the periodically tilted helix axis, leads to the energy gain of the weak signal beam. Dependence of the signal beam gain coefficient on the parameters of the short-pitch cholesteric LC is studied.

Static and dynamic electro-optical properties of liquid crystals mediated by ferroelectric polymer films

Liquid crystals (LC) can reveal the fractal dimension of multi-domain ferroelectric films (FF) while these films can control the switching time of FF–LC hybrids.

Liquid crystal control of the plasmon resonances at terahertz frequencies in graphene microribbon gratings

We theoretically study the influence of the liquid crystal (LC) orientational state on the absorption, reflection, and transmission spectra of a graphene microribbon grating placed between a nematic LC and an isotropic dielectric substrate. We calculate the absorption, reflection, and transmission coefficients at normal incidence of a far-infrared transverse magnetic wave (THz) and show that control of the orientational state of the LC layer enables the manipulation of the magnitude of the absorption and reflection maxima. The influence the LC orientational state on the plasmonic resonance increases with increasing the isotropic substrate dielectric constant and the graphene microribbon width to grating spacing ratio.

Cloaking by shells with radially inhomogeneous anisotropic permittivity

We model electromagnetic cloaking of a spherical or cylindrical nanoparticle enclosed by an optically anisotropic and optically inhomogeneous symmetric shell, by examining its electric response in a quasi-static uniform electric field. When the components of the shell permittivity are radially anisotropic and power-law dependent (ε~r(m)) whereris distance to the shell center, and m a positive or negative exponent which can be varied), the problem is analytically tractable. Formulas are calculated for the degree of cloaking in the general case, allowing the determination of a dielectric condition for the shells to be used as an invisibility cloak. Ideal cloaking is known to require that homogeneous shells exhibit an infinite ratio of tangential and radial components of the shell permittivity, but for radially inhomogeneous shells ideal cloaking can occur even for finite values of this ratio.

Observation of electron transfer between bacteria and high conductivity graphene–PEDOT composites

The direct observation of electron transfer in a system comprising bacteria and a conducting polymer substrate is reported.

Optimizing nonlinear beam coupling in low-symmetry crystals

The purpose of this paper is to find the polarizations and spatial orientations of the two interacting counterpropagating coherent light waves which ensure the largest beam coupling in monoclinic photorefractive crystal. The results of calculations are presented that are verified experimentally with Sn₂P₂S₆.

Achieving enhanced gain in photorefractive polymers by eliminating electron contributions using large bias fields

Photorefractive polymers have been extensively studied for over two decades and have found applications in holographic displays and optical image processing. The complexity of these materials arises from multiple charge contributions, for example, leading to the formation of competing photorefractive gratings. It has been recently shown that in a photorefractive polymer at relatively moderate applied electric fields the primary charge carriers (holes) establish an initial grating, followed by a subsequent competing grating (electrons) resulting in a decreased two-beam coupling and diffraction efficiencies. In this paper, it is shown that with relatively large sustainable bias fields, the two-beam coupling efficiency is enhanced owing to a decreased electron contribution. These results also explain the cause of dielectric breakdown experienced under large bias fields. Our conclusions are supported by self-pumped transient two-beam coupling and photocurrent measurements as a function of applied bias fields at different wavelengths.

Intrinsic small polarons (Sn³⁺ ions) in photorefractive Sn₂P₂S₆ crystals

Unique holelike small polarons are produced at divalent cation sites by optical excitation at low temperature in single crystals of Sn2P2S6, a monoclinic ferroelectric and photorefractive material. Electron paramagnetic resonance (EPR) is used to observe these self-trapped holes. During an illumination near 25 K with either 442 or 633 nm laser light, photoexcited holes become localized at Sn(2+) (5s(2)) ions and form paramagnetic Sn(3+) (5s(1)) ions. The Sn(3+) ions are thermally stable below 50 K. The principal values of the g matrix are 2.0031, 2.0176, and 2.0273 and the principal values of the (119)Sn hyperfine matrix are 12.828, 12.886, and 13.060 GHz. The large interaction with the (119)Sn (and (117)Sn) nucleus results in a highly asymmetric hyperfine pattern in the EPR spectrum. Weaker hyperfine interactions with two neighboring Sn ions are also observed.

A comparison of the accuracy of film-screen mammography, full-field digital mammography, and digital breast tomosynthesis

AIM

To measure the change in diagnostic accuracy of conventional film-screen mammography and full-field digital mammography (FFDM) with the addition of digital breast tomosynthesis (DBT) in women recalled for assessment following routine screening.

MATERIALS AND METHODS

Ethics approval for the study was granted. Women recalled for assessment following routine screening with screen-film mammography were invited to participate. Participants underwent bilateral, two-view FFDM and two-view DBT. Readers scored each lesion separately for probability of malignancy on screen-film mammography, FFDM, and then DBT. The scores were compared with the presence or absence of malignancy based on the final histopathology outcome.

RESULTS

Seven hundred and thirty-eight women participated (93.2% recruitment rate). Following assessment 204 (26.8%) were diagnosed as malignant (147 invasive and 57 in-situ tumours), 286 (37.68%) as benign, and 269 (35.4%) as normal. The diagnostic accuracy was evaluated by using receiving operating characteristic (ROC) and measurement of area under the curve (AUC). The AUC values demonstrated a significant (p = 0.0001) improvement in the diagnostic accuracy with the addition of DBT combined with FFDM and film-screen mammography (AUC = 0.9671) when compared to FFDM plus film-screen mammography (AUC = 0.8949) and film-screen mammography alone (AUC = 0.7882). The effect was significantly greater for soft-tissue lesions [AUC was 0.9905 with the addition of DBT and AUC was 0.9201 for FFDM with film-screen mammography combined (p = 0.0001)] compared to microcalcification [with the addition of DBT (AUC = 0.7920) and for FFDM with film-screen mammography combined (AUC = 0.7843; p = 0.3182)].

CONCLUSION

The addition of DBT increases the accuracy of mammography compared to FFDM and film-screen mammography combined and film-screen mammography alone in the assessment of screen-detected soft-tissue mammographic abnormalities.

Asymmetric Freedericksz transitions from symmetric liquid crystal cells doped with harvested ferroelectric nanoparticles

The electrical Freedericksz transition characteristics of planar aligned liquid crystal cells doped with harvested single ferroelectric domain 9 nm nanoparticles of BaTiO(3) have been measured. We demonstrate for the first time that the electrical pre-history of the cells imparts significant polarity sensitivity to the Freedericksz characteristics. The presence of harvested single domain ferroelectric nanoparticles enables cells to be programmably semi-permanently polarized. This reduces or increases the Freedericksz transition threshold by 0.8 V, depending on the polarity of the applied voltage, giving a net 1.6 V Freedericksz threshold asymmetry for 8 mum thick cells filled with TL205 liquid crystal.

Voyager planetary radio astronomy at neptune

Detection of very intense short radio bursts from Neptune was possible as early as 30 days before closest approach and at least 22 days after closest approach. The bursts lay at frequencies in the range 100 to 1300 kilohertz, were narrowband and strongly polarized, and presumably originated in southern polar regions ofthe planet. Episodes of smooth emissions in the frequency range from 20 to 865 kilohertz were detected during an interval of at least 10 days around closest approach. The bursts and the smooth emissions can be described in terms of rotation in a period of 16.11 +/- 0.05 hours. The bursts came at regular intervals throughout the encounter, including episodes both before and after closest approach. The smooth emissions showed a half-cycle phase shift between the five episodes before and after closest approach. This experiment detected the foreshock of Neptune's magnetosphere and the impacts of dust at the times of ring-plane crossings and also near the time of closest approach. Finally, there is no evidence for Neptunian electrostatic discharges.

Voyager 2 radio observations of uranus

Within distances to Uranus of about 6 x 10(6) kilometers (inbound) and 35 x 10(6) kilometers (outbound), the planetary radio astronomy experiment aboard Voyager 2 detected a wide variety of radio emissions. The emission was modulated in a period of 17.24 +/- 0.01 hours, which is identified as the rotation period of Uranus' magnetic field. Of the two poles where the axis of the off-center magnetic dipole (measured by the magnetometer experiment aboard Voyager 2) meets the planetary surface, the one closer to dipole center is now located on the nightside of the planet. The radio emission generally had maximum power and bandwidth when this pole was tipped toward the spacecraft. When the spacecraft entered the nightside hemisphere, which contains the stronger surface magnetic pole, the bandwidth increased dramatically and thereafter remained large. Dynamically evolving radio events of various kinds embedded in these emissions suggest a Uranian magnetosphere rich in magnetohydrodynamic phenomena.

Two-beam energy exchange in a hybrid photorefractive-flexoelectric liquid-crystal cell

We develop a semiquantitative theory to describe the experimentally observed energy gain when two light beams intersect in hybrid organic-inorganic photorefractives. These systems consist of a nematic liquid-crystal (LC) layer placed between two photorefractive windows. A periodic space-charge field is induced by the interfering light beams in the photorefractive windows. The field penetrates into the LC, interacting with the nematic director and giving rise to a diffraction grating. LC flexoelectricity is the principal physical mechanism driving the grating structure. Each light beam diffracts from the induced grating, leading to an apparent energy gain and loss within each beam. The LC optics is described in the Bragg regime. In the theory the exponential gain coefficient is a product of a beam interference term, a flexoelectricity term and a space-charge term. The theory has been compared with results of an experimental study on hybrid cells filled with the LC mixture TL 205. Experimentally the energy gain is maximal at much lower grating wave numbers than is predicted by naïve theory. However, if the director reorientation is cubic rather than linear in the space-charge field term, then good agreement between theory and experiment can be achieved using only a single fitting parameter. We provide a semiquantitative argument to justify this nonlinearity in terms of electric-field-induced local phase separation between different components of the liquid crystal.

Day-case angioplasty in diabetic patients with critical ischemia

AIM

Recent studies have shown that percutaneous transluminal angioplasty (PTA) can be safely performed as a day-case procedure. Many centers consider diabetes mellitus as a contraindication to day-case PTA. In this study, the safety and efficacy of 95 day-case PTA in 66 diabetic patients with critical leg ischemia (CLI) were evaluated.

METHODS

Diabetic patients with CLI were assessed in a one-stop multidisciplinary outpatient clinic. Sixty-six outpatients with CLI deemed suitable for radiological intervention by non-invasive imaging (ultrasound angiology or magnetic resonance angiography) were scheduled for day-case PTA.

RESULTS

PTA was initially successful in 63 out of 66 patients (95%). In 3 patients (5%), PTA was not possible because the lesion could not be balloon dilated or crossed with a guide wire. Clinically suspected first, second and third re-stenosis confirmed by non-invasive studies occurred in 20 out of 63 (31%), 7 out of 20 (35%) and 2 out of 7 (28%) patients, respectively. Following PTA, debridement was performed in 11 patients (17%), minor amputation in 8 (13%) and major amputation in 3 (5%). Relief of the primary symptom of rest pain or healing of ulcers was achieved in 23 out of 32 (72%) and 25 out of 27 (92.5%) patients, respectively. No peri-interventional morbidity or mortality was encountered.

CONCLUSION

PTA is feasible and safe as a day-case procedure in diabetic patients with CLI. Re-stenosis can be managed by repeat day-case PTA.

Nanoparticle doped organic-inorganic hybrid photorefractives

The gain characteristics of liquid crystal photorefractive cells doped with ferroelectric nanoparticles has been measured. The liquid crystal two beam coupling gain is found to reverse in sign and increase in magnitude through the addition of ferroelectric BaTiO(3) nanoparticles, yielding gain coefficients up to 1100 cm(-3) in the Bragg regime. We attribute the novel effects of gain reversal and magnitude increase to interactions between the ferroelectric particles' spontaneous polarization and the local liquid crystal flexopolarization.

Day-case diagnostic and interventional peripheral angiography: 10-year experience in a radiology specialist nurse-led unit

We describe a prospective evaluation of the safety of peripheral angiography procedures performed on day-case patients in a dedicated radiological nurse-led and administrated unit. Patients referred for peripheral vascular angiography, over a 10-year period, were pre-assessed by a radiology specialist nurse in a nurse-led clinic. Radiologists performed all procedures, whereas radiology specialist nurses were responsible for patient care before, during and after angiography and during the 24 h follow-up. Procedures were divided into diagnostic or interventional; complications were divided into immediate or delayed (24 h follow-up) either requiring hospital admission (major) or day-case unit management (minor). Patient acceptability was assessed using a standard questionnaire. Cost analysis was also performed. 401 day-case peripheral angiography procedures (144 diagnostic and 257 interventional) were performed in 310 patients. 109/401 (27.2%) procedures were performed on patients with diabetes mellitus. In diagnostic studies, 16/144 (11.1%) immediate and 6/144 (4.2%) delayed complications occurred whereas, in interventional studies, 65/257 (25.3%) immediate and 13/257 (5.1%) delayed complications were noted. A major complication occurred in 17/257 (6.6%) of patients in the interventional group and 3/144 (2.1%) in the diagnostic group. Puncture site haematoma was the most common complication. Nurse-led care was acceptable to the patient, with a high level of patient satisfaction seen. In conclusion, day-case diagnostic and interventional peripheral angiography procedures can be performed safely in a specialist nurse-led and administrated unit, with complication rates being within the accepted guidelines.

Direct temperature dependence measurements of dark conductivity and two-beam coupling in LiNbO3:Fe

Direct measurements of dark conductivity were conducted over a broad temperature range in LiNbO(3):Fe. These measurements were performed on a series of crystals, which were cut from the same boule and subjected to different annealing procedures (oxidized, reduced, and as-grown). Activation energies of 0.5 eV and 1.1 eV were extracted from Arrhenius plots of the dark conductivity data. The location of the Fe(2+) energy level in the band gap was determined, and is in agreement with Born's principle. A correlation between the Maxwell relaxation times and the onset of a temperature-dependent reduction in two-beam coupling efficiency was observed.

Ferroelectric-specific stark effect in stoichiometric LiNbO3:Fe at room temperature

By means of EPR spectroscopy of LiNbO(3):Fe at room temperature (RT) it is shown that the Stark effect in ferroelectric crystals can be different from that observed in other materials. Novel properties appear when an external E field reverses the direction of the spontaneous polarization, the direction of the linear Stark shift stays the same with a reversal of the E field. The corresponding spectral line shifts can occur over a long time scale (hours). These properties seem to be a general feature of the Stark effect in ferroelectric crystals when the external E field exceeds the coercive field.

Stimulated photorefractive backscatter leading to six-wave mixing and phase conjugation in iron-doped lithium niobate

The generation of multiple waves during near-oblique incidence of a 532 nm weakly focused beam on photorefractive iron-doped lithium niobate in a typical reflection geometry configuration is studied. It is shown that these waves are produced through two-wave coupling (self-diffraction) and four-wave mixing (parametric diffraction). One of these waves, the stimulated photorefractive backscatter produced from parametric diffraction, contains the self-phase conjugate. The dynamics of six-wave mixing and its dependence on crystal parameters, angle of incidence, and pump power are analyzed. What we believe to be a novel order analysis of the interaction equations provides further insight into experimental observations in the steady state. The quality of the backscatter is evaluated through image restoration, interference experiments, and visibility measurement. Reduction of two-wave coupling may significantly improve the quality of the self-phase conjugate.

Transient gain enhancement in photorefractive crystals with two types of movable charge carrier

Considerable improvement of a transient two-beam coupling gain is reported for Sn(2)P(2)S(6), a photorefractive crystal that possesses two types of movable charge carrier. A gain enhancement occurs if the phase difference of the interacting beams is abruptly changed to pi. Enhancement is also achieved with periodic phase variations of zero and pi between two discrete states at modulation frequencies lower than the smallest of two reciprocal characteristic times of the space-charge formation.

Major improvements of the photorefractive and photovoltaic properties in potassium niobate

Optical and electrical measurements have been made on a new codoped potassium niobate crystal (KNbO3:Fe,Ag) that yields a significant enhancement of the photorefractive and photovoltaic effects when compared with the published results for singly doped potassium niobate crystals. The codoped Ag impurity enters the K site, rather than the typical Nb site, thus changing the local field in the lattice. It is believed that Fe perturbed by the Ag in the K site is responsible for an enhancement of the linear absorption and photocurrent, as well as a probable increase in the effective trap density. An enhanced trap density is likely the cause of the increased photorefractive counterpropagating two-beam coupling efficiency.

Red blood cell membrane essential fatty acid metabolism in early psychotic patients following antipsychotic drug treatment

A role of indices of oxidative stress, oxidative injury, and abnormal membrane phospholipid, specifically the phospholipid essential polyunsaturated fatty acids (EPUFAs) metabolism has been suggested based on studies in separate groups of patients with or without medication. The current study investigated the relationship between these biochemical measures in first-episode psychotic patients (N=16) at baseline and after 6 months of antipsychotic treatment (N=5 each with risperidone and olanzapine) and compared them to matched normal subjects. The indices of oxidative stress included: antioxidant enzymes; superoxide dismutase, glutathione peroxidase and catalase; and the oxidative injury as the levels of plasma lipid peroxides. The key membrane EPUFA's been; linolenic acid, arachidonic acid, nervonic acid, docosapentaenoic acid and docosahexaenoic acid. Furthermore, the changes in these biochemical measures were correlated with clinical symptomatology. Data indicated that, at baseline, reduced levels of antioxidant enzymes were associated with increased plasma lipid peroxides and reduced membrane EPUFAs, particularly omega-3 fatty acids. Furthermore, these biochemical measures normalized after 6 months of antipsychotic treatment. Parallel-improved psychopathology indicated that membrane EPUFA status might be partly affected by oxidative damage, which together may contribute to the pathophysiology and thereby, psychopathology of schizophrenia. These data also support the augmentation of antipsychotic treatment by supplementation with a combination of antioxidants and omega-3 fatty acids.

Differential effects of chronic haloperidol and olanzapine exposure on brain cholinergic markers and spatial learning in rats

RATIONALE

In psychiatric patients, haloperidol (HAL) induces a number of adverse extrapyramidal and cognitive symptoms, which appear to be less problematic with olanzapine (OLZ). In animals, HAL may initiate a number of harmful effects on central nervous system neurons, including damage to cholinergic pathways - an effect that could be especially deleterious to those experiencing memory dysfunction. The identification of the neurobiological substrates of such effects in animal models may help to improve the algorithms used for proper drug selection especially for long-term neuroleptic use.

OBJECTIVES

The aim of this study was to compare the effects of chronic (45-day and 90-day), continuous oral exposure to HAL with OLZ for effects on cognitive performance and cholinergic markers in rats.

METHODS

After chronic neuroleptic exposure (and a 4-day washout) spatial memory performance was measured in a water maze task, and choline acetyltransferase (ChAT) immunoreactivity was assessed with immunofluorescence staining.

RESULTS

In water maze experiments, HAL and OLZ (relative to vehicle) administered for 90 days (but not 45 days) significantly impaired learning performance (i.e., higher mean latencies across several trials to reach a hidden platform). HAL administered for 90 days was associated with impairment across a greater number of trials than OLZ and it also impaired probe trial performance, as indicated by a reduced number of crossings over the previous platform area (when compared with OLZ or vehicle). Both 45 days and 90 days of HAL treatment reduced ChAT staining in the cortex and hippocampus when compared with OLZ or vehicle.

CONCLUSIONS

The results in the rat suggest that OLZ (relative to HAL) may be more desirable as an antipsychotic for patients suffering from memory dysfunction especially for those in which cholinergic deficits may already be present.

Contra-directional two-beam coupling by use of a single input beam in an iron-doped lithium niobate multimode fiber

Experimental results are presented for 1,800 contra-directional two-beam coupling (TBC) measurements in a single crystal fiber of LiNbO8:Fe using a single incident beam and its Fresnel reflection off the back surface of the fiber. To our knowledge, this is the first time that volume gratings have been written in a fiber using this beam coupling geometry. At small f-numbers, the TBC efficiency has been predicted to decrease in bulk LiNbO3:Fe due to the erasure of the weak gratings by the dark conductivity. We present experimental results validating the published theory and show experimentally that confinement of the interfering beams in a fiber geometry overcomes this limitation.

A novel carbamoyl-phosphate synthetase from Aquifex aeolicus

Aquifex aeolicus, an extreme hyperthermophile, has neither a full-length carbamoyl-phosphate synthetase (CPSase) resembling the enzyme found in all mesophilic organisms nor a carbamate kinase-like CPSase such as those present in several hyperthermophilic archaea. However, the genome has open reading frames encoding putative proteins that are homologous to the major CPSase domains. The glutaminase, CPS.A, and CPS.B homologs from A. aeolicus were cloned, overexpressed in Escherichia coli, and purified to homogeneity. The isolated proteins could catalyze several partial reactions but not the overall synthesis of carbamoyl phosphate. However, a stable 124-kDa complex could be reconstituted from stoichiometric amounts of CPS.A and CPS.B proteins that synthesized carbamoyl phosphate from ATP, bicarbonate, and ammonia. The inclusion of the glutaminase subunit resulted in the formation of a 171-kDa complex that could utilize glutamine as the nitrogen-donating substrate, although the catalytic efficiency was significantly compromised. Molecular modeling, using E. coli CPSase as a template, showed that the enzyme has a similar structural organization and interdomain interfaces and that all of the residues known to be essential for function are conserved and properly positioned. A steady state kinetic study at 78 degrees C indicated that although the substrate affinity was similar for bicarbonate, ammonia, and glutamine, the K(m) for ATP was appreciably higher than that of any known CPSase. The A. aeolicus complex, with a split gene encoding the major synthetase domains and relatively inefficient coupling of amidotransferase and synthetase functions, may be more closely related to the ancestral precursor of contemporary mesophilic CPSases.

Reduced protein phosphatase 2A activity induces hyperphosphorylation and altered compartmentalization of tau in transgenic mice

Hyperphosphorylated isoforms of the microtubule-associated protein tau are the major components of neurofibrillary lesions in Alzheimer's disease (AD). Protein phosphatase (PP) 2A is a major phosphatase implicated in tau dephosphorylation in vitro. Dephosphorylation of tau can be blocked in vivo by okadaic acid, a potent inhibitor of PP2A. Moreover, activity of PP2A is reduced in AD brains. To elucidate the role of PP2A in tau phosphorylation and pathogenesis, we expressed a dominant negative mutant form of the catalytic subunit Calpha of PP2A, L199P, in mice by using a neuron-specific promoter. We obtained mice with high expression levels of Calpha L199P in cortical, hippocampal, and cerebellar neurons. PP2A activity in brain homogenates of transgenic mice was reduced to 66%. Endogenous tau protein was hyperphosphorylated at distinct sites including the AT8 epitope Ser-202/Thr-205, a major AD-associated tau phosphoepitope. AT8-positive tau aggregates accumulated in the soma and dendrites of cortical pyramidal cells and cerebellar Purkinje cells and co-localized with ubiquitin. Our data establish that PP2A plays a crucial role in tau phosphorylation. Our results also show that reduced PP2A activity is associated with altered compartmentalization and ubiquitination of tau, resembling a key pathological finding in AD.

Cloning, expression, and structure analysis of carbamate kinase-like carbamoyl phosphate synthetase from Pyrococcus abyssi

Pyrococcus abyssi, a hyperthermophilic archaeon found in the vicinity of deep-sea hydrothermal vents, grows optimally at temperatures around 100 degrees C. Carbamoyl phosphate synthetase (CPSase) from this organism was cloned and sequenced. The active 34-kDa recombinant protein was overexpressed in Escherichia coli when the host cells were cotransformed with a plasmid encoding tRNA synthetases for low-frequency Escherichia coli codons. Sequence homology suggests that the tertiary structure of P. abyssi CPSase, resembling its counterpart in Pyrococcus furiosus, is closely related to the catabolic carbamate kinases and is very different from the larger mesophilic CPSases. P. furiosus CPSase and carbamate kinase form carbamoyl phosphate by phosphorylating carbamate produced spontaneously in solution from ammonia and bicarbonate. In contrast, P. abyssi CPSase has intrinsic bicarbonate-dependent ATPase activity, suggesting that the enzyme can catalyze the phosphorylation of the isosteric substrates carbamate and bicarbonate.

Active-site mutations impairing the catalytic function of the catalytic subunit of human protein phosphatase 2A permit baculovirus-mediated overexpression in insect cells

Members of the phosphoprotein phosphatase (PPP) family of protein serine/threonine phosphatases, including protein phosphatase (PP)1, PP2A and PP2B, share invariant active-site residues that are critical for catalytic function [Zhuo, Clemens, Stone and Dixon (1994) J. Biol. Chem. 269, 26234-26238]. Mutation of the active-site residues Asp(88) or His(118) within the human PP2A catalytic subunit (PP2Ac)alpha impaired catalytic activity in vitro; the D88N and H118N substitutions caused a 9- and 23-fold reduction in specific activity respectively, when compared with wild-type recombinant PP2Ac, indicating an important role for these residues in catalysis. Consistent with this, the D88N and H118N substituted forms failed to provide PP2A function in vivo, because, unlike wild-type human PP2Acalpha, neither substituted for the endogenous PP2Ac enzyme of budding yeast. Relative to wild-type PP2Ac, the active-site mutants were dramatically overexpressed in High Five insect cells using the baculovirus system. Milligram quantities of PP2Ac were purified from 1x10(9) High Five cells and the kinetic constants for dephosphorylation of the peptide RRA(pT)VA (single-letter amino-acid notation) by PP2Ac (K(m)=337.5 microM; k(cat)=170 s(-1)) and D88N (K(m)=58.4 microM; k(cat)=2 s(-1)) were determined. The results show that the substitution impairs catalysis severely without a significant effect on substrate binding, consistent with the PPP catalytic mechanism. Combination of the baculovirus and yeast systems provides a strategy whereby the structure-function of PP2Ac may be fully explored, a goal which has previously proven difficult, owing to the stringent auto-regulatory control of PP2Ac protein levels in vivo.

Targeted and extended acetylation of histones H4 and H3 at active and inactive genes in chicken embryo erythrocytes

Affinity-purified polyclonal antibodies recognizing the most highly acetylated forms of histones H3 and H4 were used in immunoprecipitation assays with chromatin fragments derived from 15-day chicken embryo erythrocytes by micrococcal nuclease digestion. The distribution of hyperacetylated H4 and H3 was mapped at the housekeeping gene, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and the tissue-specific gene, carbonic anhydrase (CA). H3 and H4 acetylation was found targeted to the CpG island region at the 5' end of both these genes, falling off in the downstream direction. In contrast, at the beta(A)-globin gene, both H3 and H4 are highly acetylated throughout the gene and at the downstream enhancer, with a maximum at the promoter. Low level acetylation was observed at the 5' end of the inactive ovalbumin gene. Run-on assays to measure ongoing transcription showed that the GAPDH and CA genes are transcribed at a much lower rate than the adult beta(A)-globin gene. The extensive high level acetylation at the beta(A)-globin gene correlates most simply with its high rate of transcription. The targeted acetylation of histones H3 and H4 at the GAPDH and CA genes is consistent with a role in transcriptional initiation and implies that transcriptional elongation does not necessarily require hyperacetylation.

The predicted beta12-beta13 loop is important for inhibition of PP2Acalpha by the antitumor drug fostriecin

The potential anticancer agent fostriecin (FOS) is a potent inhibitor of the protein Ser/Thr phosphatases PP2A and PP4 and a weaker inhibitor of PP1. Random mutagenesis and automated screening in yeast identified residues in human PP2Acalpha important for inhibitory FOS binding. A C269S substitution in the predicted beta12-beta13 loop decreased the FOS sensitivity of intact cells and increased the IC(50) of PP2Acalpha by 10-fold in vitro. Changing PP2Acalpha Cys-269 to phenylalanine, the equivalent residue in PP1, and the Y267G and G270D substitutions caused a similar effect. The results provide information relevant to the design of novel protein Ser/Thr phosphatase inhibitory drugs.

Vitamin B12 and folate bioavailability from two prenatal multivitamin/multimineral supplements

In this crossover, single-blind study, the bioavailability of B12 and folate, fasting and postprandially, was measured in 30 pregnant women for two prenatal multivitamin/multimineral supplements (Stuartnatal Plus and Materna, Wyeth-Ayerst Pharmaceuticals, Philadelphia, PA) and a placebo. Blood samples were obtained before supplementation and at 1, 3, 6, and 8 hr after supplementation serum levels of the two vitamins were measured by radioimmunoassay. The maximum postabsorption serum level was multiplied by the total body plasma levels to obtain the total rate of body absorption. The absorption peak of both vitamins occurred at 3 hours after ingestion of a supplement. The total body absorption of the two vitamins was greater during fasting than it was postprandially. There was 30% greater B12 absorption for Stuartnatal Plus (371 +/- 56 vs. 285 +/- 34 pmol) and 33% for Materna (315 +/- 34 vs. 236 +/- 4 pmol, p < or = 0.05). Similarly, there was 117% greater folate absorption fasting for Stuartnatal Plus (163 +/- 15 vs. 75 +/- 15 nmol, p < or = 0.001) and 57% greater absorption for Materna (207 +/- 21 vs. 132 +/- 13 nmol, p < or = 0.01). Both vitamins were readily absorbed (within 3 hours) into the maternal hepatic portal circulation. The absorption of both vitamins was significantly less when ingested after the test meal than when fasting.

Mutation of the C-terminal leucine residue of PP2Ac inhibits PR55/B subunit binding and confers supersensitivity to microtubule destabilization in Saccharomyces cerevisiae

Protein phosphatase 2A is ubiquitous among eukaryotes and exists as a family of holoenzymes in which the catalytic subunit. PP2Ac, binds a variety of regulatory subunits. Using the yeast Saccharomyces cerevisia, we have investigated the role of the phylogenetically invariant C-terminal leucine residue of PP2Ac, which, in mammalian cells, undergoes reversible methylation and modulates binding of the PR55/B subunit. In S. cerevisiae, the C-terminal Leu-377 residue of Pph22p (equivalent to human PP2Ac Leu-309) was dispensable for cell growth under optimum conditions and its removal, or substitution by alanine, did not inhibit PP2A activity in vitro. However, Leu-377 is required for binding of the yeast PR55/B subunit, Cdc55p, by Pph22p, though apparently not for the binding of Rts1p, the yeast PR61/B' subunit. Furthermore, mutation of this leucine enhanced the sensitivity of cells to microtubule destabilization, a defect characteristic of cdc55delta mutant cells, which are impaired for spindle checkpoint function. These results demonstrate that the regulation of PP2A, mediated by PR55/B binding to the highly conserved PP2Ac C-terminus, is critical for cell viability under conditions of microtubule damage and support a role for PP2A in exit from mitosis.

Radiography versus spiral CT in the evaluation of cervicothoracic junction injuries in polytrauma patients who have undergone intubation

A prospective study was performed over a 1-year period in patients who had sustained blunt trauma, mostly in motor vehicle accidents. All 73 patients (56 male and 17 female; age range, 2-94 years; mean age, 35.2 years) in the study had undergone intubation and ventilation at the trauma site (mean Glasgow Coma Score, 9.9 [range, 3-15]; mean Injury Severity Score, 30.4 [range, 8-75]) and subsequently underwent three-view radiography of the cervical spine and thin-section spiral computed tomography (CT) of the cervicothoracic junction. Spinal fractures were detected in 20 patients and involved the cervicothoracic junction region in 12 cases. In all 12 patients, the fractures were visualized at CT, whereas in seven of 12 patients, conventional radiography failed to demonstrate injuries (transverse process fracture of T1 [n = 1], pedicle and vertebral body fracture of C7 [n = 1], fractures of the first and second ribs [n = 5]). Thus, routine CT of the cervicothoracic junction in a highly select group of severely injured patients helped detect occult fracture in seven of 73 patients (10%); however, most of these fractures were not clinically significant. Larger studies involving a high-risk patient population are needed to confirm these findings.

Important role for phylogenetically invariant PP2Acalpha active site and C-terminal residues revealed by mutational analysis in Saccharomyces cerevisiae

PP2A is a central regulator of eukaryotic signal transduction. The human catalytic subunit PP2Acalpha functionally replaces the endogenous yeast enzyme, Pph22p, indicating a conservation of function in vivo. Therefore, yeast cells were employed to explore the role of invariant PP2Ac residues. The PP2Acalpha Y127N substitution abolished essential PP2Ac function in vivo and impaired catalysis severely in vitro, consistent with the prediction from structural studies that Tyr-127 mediates substrate binding and its side chain interacts with the key active site residues His-118 and Asp-88. The V159E substitution similarly impaired PP2Acalpha catalysis profoundly and may cause global disruption of the active site. Two conditional mutations in the yeast Pph22p protein, F232S and P240H, were found to cause temperature-sensitive impairment of PP2Ac catalytic function in vitro. Thus, the mitotic and cell lysis defects conferred by these mutations result from a loss of PP2Ac enzyme activity. Substitution of the PP2Acalpha C-terminal Tyr-307 residue by phenylalanine impaired protein function, whereas the Y307D and T304D substitutions abolished essential function in vivo. Nevertheless, Y307D did not reduce PP2Acalpha catalytic activity significantly in vitro, consistent with an important role for the C terminus in mediating essential protein-protein interactions. Our results identify key residues important for PP2Ac function and characterize new reagents for the study of PP2A in vivo.

Blood cell lead, calcium, and magnesium levels associated with pregnancy-induced hypertension and preeclampsia

This study compares the red blood cell (Rbc) levels of lead (Pb), calcium (Ca), and magnesium (Mg) in relation to blood pressure in 39 pregnant women in the third trimester of pregnancy. The study population included 20 women with normal pregnancies, 15 with mild hypertension, and 4 with severe hypertension and preeclampsia. The mean +/- SD for each group was calculated and the difference between the means of the normotensive and the other groups were compared by analysis of variance. Significant differences from normal to the preeclamptic pregnancies were in (1) elevated Rbc Pb (p < or = 0.001), (2) lower Rbc Ca (p < or = 0.001), and (3) lower Rbc Mg/Pb ratio (p < or = 0.0001). Pearson's rank correlation between blood pressure showed a direct relation to the Rbc Pb level (p < or = 0.01) and an inverse relation to the Rbc Ca and Mg/Pb ratio (p < or = 0.004, < or = 0.007). Apparently, prenatal blood pressure is directly proportional to Rbc Pb content and related or modified by Rbc Ca and Mg.

Bioavailability of iron in two prenatal multivitamin/multimineral supplements

OBJECTIVE

To determine the iron bioavailability in two popular prenatal multivitamin/multimineral supplement tablets containing 27 mg elemental iron.

STUDY DESIGN

Iron absorption during an eight-hour period following ingestion of a multivitamin/multimineral formulation, both fasting and with a standardized meal, was measured in a group of 30 pregnant women (24-32 weeks of gestation) and statistically compared. The prenatal formulations were Stuartnatal Plus and Materna (Wyeth-Ayerst Pharmaceuticals, Philadelphia, Pennsylvania), and each contains 27 mg of elemental iron. A placebo was included in the study for the control group in this crossover, single-blind study.

RESULTS

The net iron bioavailability (mean +/- SE) of Stuartnatal Plus and Materna, accounting for diurnal variation, and the iron ingested with the standardized meal was 5.4 +/- 0.4 and 4.6 +/- 0.2 mg, respectively, while fasting and 2.9 +/- 0.4 and 2.7 +/- 0.4 mg, respectively, postprandially. The total amount of iron absorption in the fasting states from both prenatal formulations exceeded the 3 mg of supplemental iron absorption per day recommended by the National Academy of Sciences.

CONCLUSION

The results of this study indicate that these two prenatal multivitamin/multimineral formulations provide > 3.0 mg of supplemental iron absorption (fasting) as recommended by the National Academy of Sciences and 2.7 mg of iron absorption above the levels achieved following ingestion of a standard, low-iron test meal.

Seminal plasma trace metal levels in industrial workers

This study compares the seminal plasma trace metal levels of hospital workers with groups of industrial workers in a petroleum refinery, smelter, and chemical plant. The metals measured were the essential metals (copper, zinc, nickel, cobalt, and manganese) and the toxic metals (lead, cadmium, and aluminum). The group mean +/- SE metal level for each group (50 subjects per group) was calculated, and the statistical significance of the group mean differences of the industrial groups with the hospital group (control) was determined by the Student's t-test. The differences observed in the smelter group were increased copper and zinc (p < or = 0.001) and decreased nickel, cobalt, and manganese (p < or = 0.001, < or = 0.01). The refinery group differences were increased copper, zinc, and nickel (p < or = 0.001) but decreased cobalt and manganese (p < or = 0.001). The chemical group differences were increased zinc (p < or = 0.001) and decreased cobalt (p < or = 0.001). The seminal plasma levels of the toxic metals lead and aluminum were increased in each of the industrial groups (p < or = 0.001). Concurrent differences were (1) decreased accumulation of nickel, cobalt, and manganese in the smelter group, (2) decreased cobalt and manganese in the refinery group, and (3) only decreased cobalt in the chemical group.

The crystal structure of human eukaryotic release factor eRF1--mechanism of stop codon recognition and peptidyl-tRNA hydrolysis

The release factor eRF1 terminates protein biosynthesis by recognizing stop codons at the A site of the ribosome and stimulating peptidyl-tRNA bond hydrolysis at the peptidyl transferase center. The crystal structure of human eRF1 to 2.8 A resolution, combined with mutagenesis analyses of the universal GGQ motif, reveals the molecular mechanism of release factor activity. The overall shape and dimensions of eRF1 resemble a tRNA molecule with domains 1, 2, and 3 of eRF1 corresponding to the anticodon loop, aminoacyl acceptor stem, and T stem of a tRNA molecule, respectively. The position of the essential GGQ motif at an exposed tip of domain 2 suggests that the Gln residue coordinates a water molecule to mediate the hydrolytic activity at the peptidyl transferase center. A conserved groove on domain 1, 80 A from the GGQ motif, is proposed to form the codon recognition site.