The impact of low-mode symmetry on inertial fusion energy output in the burning plasma state

Indirect Drive Inertial Confinement Fusion Experiments on the National Ignition Facility (NIF) have achieved a burning plasma state with neutron yields exceeding 170 kJ, roughly 3 times the prior record and a necessary stage for igniting plasmas. The results are achieved despite multiple sources of degradations that lead to high variability in performance. Results shown here, for the first time, include an empirical correction factor for mode-2 asymmetry in the burning plasma regime in addition to previously determined corrections for radiative mix and mode-1. Analysis shows that including these three corrections alone accounts for the measured fusion performance variability in the two highest performing experimental campaigns on the NIF to within error. Here we quantify the performance sensitivity to mode-2 symmetry in the burning plasma regime and apply the results, in the form of an empirical correction to a 1D performance model. Furthermore, we find the sensitivity to mode-2 determined through a series of integrated 2D radiation hydrodynamic simulations to be consistent with the experimentally determined sensitivity only when including alpha-heating.

Achievement of Target Gain Larger than Unity in an Inertial Fusion Experiment

On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

Design of the first fusion experiment to achieve target energy gain G>1

In this work we present the design of the first controlled fusion laboratory experiment to reach target gain G>1 N221204 (5 December 2022) [Phys. Rev. Lett. 132, 065102 (2024)10.1103/PhysRevLett.132.065102], performed at the National Ignition Facility, where the fusion energy produced (3.15 MJ) exceeded the amount of laser energy required to drive the target (2.05 MJ). Following the demonstration of ignition according to the Lawson criterion N210808, experiments were impacted by nonideal experimental fielding conditions, such as increased (known) target defects that seeded hydrodynamic instabilities or unintentional low-mode asymmetries from nonuniformities in the target or laser delivery, which led to reduced fusion yields less than 1 MJ. This Letter details design changes, including using an extended higher-energy laser pulse to drive a thicker high-density carbon (also known as diamond) capsule, that led to increased fusion energy output compared to N210808 as well as improved robustness for achieving high fusion energies (greater than 1 MJ) in the presence of significant low-mode asymmetries. For this design, the burnup fraction of the deuterium and tritium (DT) fuel was increased (approximately 4% fuel burnup and a target gain of approximately 1.5 compared to approximately 2% fuel burnup and target gain approximately 0.7 for N210808) as a result of increased total (DT plus capsule) areal density at maximum compression compared to N210808. Radiation-hydrodynamic simulations of this design predicted achieving target gain greater than 1 and also the magnitude of increase in fusion energy produced compared to N210808. The plasma conditions and hotspot power balance (fusion power produced vs input power and power losses) using these simulations are presented. Since the drafting of this manuscript, the results of this paper have been replicated and exceeded (N230729) in this design, together with a higher-quality diamond capsule, setting a new record of approximately 3.88MJ of fusion energy and fusion energy target gain of approximately 1.9.

Observations and properties of the first laboratory fusion experiment to exceed a target gain of unity

An indirect-drive inertial fusion experiment on the National Ignition Facility was driven using 2.05 MJ of laser light at a wavelength of 351 nm and produced 3.1±0.16 MJ of total fusion yield, producing a target gain G=1.5±0.1 exceeding unity for the first time in a laboratory experiment [Phys. Rev. E 109, 025204 (2024)10.1103/PhysRevE.109.025204]. Herein we describe the experimental evidence for the increased drive on the capsule using additional laser energy and control over known degradation mechanisms, which are critical to achieving high performance. Improved fuel compression relative to previous megajoule-yield experiments is observed. Novel signatures of the ignition and burn propagation to high yield can now be studied in the laboratory for the first time.

Reduced mixing in inertial confinement fusion with early-time interface acceleration

In inertial confinement fusion (ICF) implosions, the interface between the cryogenic DT fuel and the ablator is unstable to shock acceleration (the Richtmyer-Meshkov instability, RM) and constant acceleration (Rayleigh-Taylor instability, RT). Instability growth at this interface can reduce the final compression, limiting fusion burnup. If the constant acceleration is in the direction of the lighter material (negative Atwood number), the RT instability produces oscillatory motion that can stabilize against RM growth. Theory and simulations suggest this scenario occurred at early times in some ICF experiments on the National Ignition Facility, possibly explaining their favorable performance compared to one-dimensional simulations. This characteristic is being included in newer, lower adiabat designs, seeking to improve compression while minimizing ablator mixing into the fuel.

Nonlinear ablative Rayleigh-Taylor instability: Increased growth due to self-generated magnetic fields

The growth rate of the nonlinear ablative Rayleigh-Taylor (RT) instability is enhanced by magnetic fields self-generated by the Biermann battery mechanism; a scaling for this effect with perturbation height and wavelength is proposed and validated with extended-magnetohydrodynamic simulations. The magnetic flux generation rate around a single RT spike is found to scale with the spike height. The Hall parameter, which quantifies electron magnetization, is found to be strongly enhanced for short-wavelength spikes due to Nernst compression of the magnetic field at the spike tip. The impact of the magnetic field on spike growth is through both the suppressed thermal conduction into the unstable spike and the Righi-Leduc heat flow deflecting heat from the spike tip to the base. Righi-Leduc is found to be the dominant effect for small Hall parameters, while suppressed thermal conduction dominates for large Hall parameters. These results demonstrate the importance of considering magnetic fields in all perturbed inertial confinement fusion hot spots.

Lawson Criterion for Ignition Exceeded in an Inertial Fusion Experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

Experimental achievement and signatures of ignition at the National Ignition Facility

An inertial fusion implosion on the National Ignition Facility, conducted on August 8, 2021 (N210808), recently produced more than a megajoule of fusion yield and passed Lawson's criterion for ignition [Phys. Rev. Lett. 129, 075001 (2022)10.1103/PhysRevLett.129.075001]. We describe the experimental improvements that enabled N210808 and present the first experimental measurements from an igniting plasma in the laboratory. Ignition metrics like the product of hot-spot energy and pressure squared, in the absence of self-heating, increased by ∼35%, leading to record values and an enhancement from previous experiments in the hot-spot energy (∼3×), pressure (∼2×), and mass (∼2×). These results are consistent with self-heating dominating other power balance terms. The burn rate increases by an order of magnitude after peak compression, and the hot-spot conditions show clear evidence for burn propagation into the dense fuel surrounding the hot spot. These novel dynamics and thermodynamic properties have never been observed on prior inertial fusion experiments.

Design of an inertial fusion experiment exceeding the Lawson criterion for ignition

We present the design of the first igniting fusion plasma in the laboratory by Lawson's criterion that produced 1.37 MJ of fusion energy, Hybrid-E experiment N210808 (August 8, 2021) [Phys. Rev. Lett. 129, 075001 (2022)10.1103/PhysRevLett.129.075001]. This design uses the indirect drive inertial confinement fusion approach to heat and compress a central "hot spot" of deuterium-tritium (DT) fuel using a surrounding dense DT fuel piston. Ignition occurs when the heating from absorption of α particles created in the fusion process overcomes the loss mechanisms in the system for a duration of time. This letter describes key design changes which enabled a ∼3-6× increase in an ignition figure of merit (generalized Lawson criterion) [Phys. Plasmas 28, 022704 (2021)1070-664X10.1063/5.0035583, Phys. Plasmas 25, 122704 (2018)1070-664X10.1063/1.5049595]) and an eightfold increase in fusion energy output compared to predecessor experiments. We present simulations of the hot-spot conditions for experiment N210808 that show fundamentally different behavior compared to predecessor experiments and simulated metrics that are consistent with N210808 reaching for the first time in the laboratory "ignition."

Impact of Localized Radiative Loss on Inertial Confinement Fusion Implosions

The impact to fusion energy production due to the radiative loss from a localized mix in inertial confinement implosions using high density carbon capsule targets has been quantified. The radiative loss from the localized mix and local cooling of the reacting plasma conditions was quantified using neutron and x-ray images to reconstruct the hot spot conditions during thermonuclear burn. Such localized features arise from ablator material that is injected into the hot spot from the Rayleigh-Taylor growth of capsule surface perturbations, particularly the tube used to fill the capsule with deuterium and tritium fuel. Observations, consistent with analytic estimates, show the degradation to fusion energy production to be linearly proportional to the fraction of the total emission that is associated with injected ablator material and that this radiative loss has been the primary source of variations, of up to 1.6 times, in observed fusion energy production. Reducing the fill tube diameter has increased the ignition metric χ_{no α} from 0.49 to 0.72, 92% of that required to achieve a burning hot spot.

Publisher's Note: X-ray shadow imprint of hydrodynamic instabilities on the surface of inertial confinement fusion capsules by the fuel fill tube [Phys. Rev. E 95, 031204(R) (2017)]

This corrects the article DOI: 10.1103/PhysRevE.95.031204.

X-ray shadow imprint of hydrodynamic instabilities on the surface of inertial confinement fusion capsules by the fuel fill tube

Measurements of hydrodynamic instability growth for a high-density carbon ablator for indirectly driven inertial confinement fusion implosions on the National Ignition Facility are reported. We observe significant unexpected features on the capsule surface created by shadows of the capsule fill tube, as illuminated by laser-irradiated x-ray spots on the hohlraum wall. These shadows increase the spatial size and shape of the fill tube perturbation in a way that can significantly degrade performance in layered implosions compared to previous expectations. The measurements were performed at a convergence ratio of ∼2 using in-flight x-ray radiography. The initial seed due to shadow imprint is estimated to be equivalent to ∼50-100 nm of solid ablator material. This discovery has prompted the need for a mitigation strategy for future inertial confinement fusion designs as proposed here.

Improved Performance of High Areal Density Indirect Drive Implosions at the National Ignition Facility using a Four-Shock Adiabat Shaped Drive

Hydrodynamic instabilities can cause capsule defects and other perturbations to grow and degrade implosion performance in ignition experiments at the National Ignition Facility (NIF). Here, we show the first experimental demonstration that a strong unsupported first shock in indirect drive implosions at the NIF reduces ablation front instability growth leading to a 3 to 10 times higher yield with fuel ρR>1  g/cm(2). This work shows the importance of ablation front instability growth during the National Ignition Campaign and may provide a path to improved performance at the high compression necessary for ignition.

Differential ablator-fuel adiabat tuning in indirect-drive implosions

We propose a design adjustment to the high foot laser pulse [T. R. Dittrich et al., Phys. Rev. Lett. 112, 055002 (2014)] that is predicted to lower the fuel adiabat, increase compression and neutron production, but maintain similar ablation front growth. This is accomplished by lowering the laser power between the first and the second pulses (the "trough") so that the first shock remains strong initially but decays as it transits the ablator and enters the capsule fuel in a process similar to direct-drive "adiabat shaping" [S. E. Bodner et al., Phys. Plasmas 7, 2298 (2000)]. Integrated hohlraum simulations show that hohlraum cooling is sufficient to launch decaying shocks with adequate symmetry control, suggesting that adiabat shaping may be possible with indirect-drive implosions. Initial experiments show the efficacy of this technique.

Normal range of bleeding scores for the ISTH-BAT: adult and pediatric data from the merging project

Bleeding Assessment Tools (BATs) have been developed to aid in the standardized evaluation of bleeding symptoms. The Vicenza Bleeding Questionnaire (BQ), published in 2005, established a common framework and scoring key that has undergone subsequent modification over the years, culminating in the publication of the ISTH-BAT in 2010. Understanding the normal range of bleeding scores is critical when assessing the utility of a BAT. Within the context of The Merging Project, a bioinformatics system was created to facilitate the merging of legacy data derived from four different (but all Vicenza-based) BATs; the MCMDM1-VWD BQ, the Condensed MCMDM-1VWD BQ, the Pediatric Bleeding Questionnaire and the ISTH-BAT. Data from 1040 normal adults and 328 children were included in the final analysis, which showed that the normal range is 0-3 for adult males, 0-5 for adult females and 0-2 in children for both males and females. Therefore, the cut-off for a positive or abnormal BS is ≥4 in adult males, ≥6 in adult females and ≥3 in children. This information can now be used to objectively assess bleeding symptoms as normal or abnormal in future studies.

Reduced instability growth with high-adiabat high-foot implosions at the National Ignition Facility

Hydrodynamic instabilities are a major obstacle in the quest to achieve ignition as they cause preexisting capsule defects to grow and ultimately quench the fusion burn in experiments at the National Ignition Facility. Unstable growth at the ablation front has been dramatically reduced in implosions with "high-foot" drives as measured using x-ray radiography of modulations at the most dangerous wavelengths (Legendre mode numbers of 30-90). These growth reductions have helped to improve the performance of layered DT implosions reported by O. A. Hurricane et al. [Nature (London) 506, 343 (2014)], when compared to previous "low-foot" experiments, demonstrating the value of stabilizing ablation-front growth and providing directions for future ignition designs.

First measurements of hydrodynamic instability growth in indirectly driven implosions at ignition-relevant conditions on the National Ignition Facility

Ignition experiments have shown an anomalous susceptibility to hydrodynamic instability growth. To help understand these results, the first hydrodynamic instability growth measurements in indirectly driven implosions on the National Ignition Facility were performed at ignition conditions with peak radiation temperatures up to ∼300  eV. Plastic capsules with two-dimensional preimposed, sinusoidal outer surface modulations of initial wavelengths of 240 (corresponding to a Legendre mode number of 30), 120 (mode 60), and 80  μm (mode 90) were imploded by using actual low-adiabat ignition laser pulses. The measured growth was in excellent agreement, validating 2D hydra simulations for the most dangerous modes in the acceleration phase. These results reinforce confidence in the predictive capability of calculations that are paramount to illuminating the path toward ignition.

Inhibition of turbulence in inertial-confinement-fusion hot spots by viscous dissipation

Achieving ignition in inertial confinement fusion (ICF) requires the formation of a high-temperature (>10 keV) central hot spot. Turbulence has been suggested as a mechanism for degrading the hot-spot conditions by altering transport properties, introducing colder, mixed material, or reducing the conversion of radially directed kinetic energy to hot-spot heating. We show, however, that the hot spot is very viscous, and the assumption of turbulent conditions in the hot spot is incorrect. This work presents the first high-resolution, three-dimensional simulations of National Ignition Facility (NIF) implosion experiments using detailed knowledge of implosion dynamics and instability seeds and including an accurate model of physical viscosity. We find that when viscous effects are neglected, the hot spot can exhibit a turbulent kinetic energy cascade. Viscous effects, however, are significant and strongly damp small-scale velocity structures, with a hot-spot Reynolds number in the range of only 10-100.

Measurements of an ablator-gas atomic mix in indirectly driven implosions at the National Ignition Facility

We present the first results from an experimental campaign to measure the atomic ablator-gas mix in the deceleration phase of gas-filled capsule implosions on the National Ignition Facility. Plastic capsules containing CD layers were filled with tritium gas; as the reactants are initially separated, DT fusion yield provides a direct measure of the atomic mix of ablator into the hot spot gas. Capsules were imploded with x rays generated in hohlraums with peak radiation temperatures of ∼294  eV. While the TT fusion reaction probes conditions in the central part (core) of the implosion hot spot, the DT reaction probes a mixed region on the outer part of the hot spot near the ablator-hot-spot interface. Experimental data were used to develop and validate the atomic-mix model used in two-dimensional simulations.

Onset of hydrodynamic mix in high-velocity, highly compressed inertial confinement fusion implosions

Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to 7×10(14), and record fuel areal densities of 0.7 to 1.3 g/cm2. These implosions use hohlraums irradiated with shaped laser pulses of 1.5-1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.

Numerical modeling of the sensitivity of x-ray driven implosions to low-mode flux asymmetries

The sensitivity of inertial confinement fusion implosions, of the type performed on the National Ignition Facility (NIF) [1], to low-mode flux asymmetries is investigated numerically. It is shown that large-amplitude, low-order mode shapes (Legendre polynomial P(4), resulting from low-order flux asymmetries, cause spatial variations in capsule and fuel momentum that prevent the deuterium and tritium (DT) "ice" layer from being decelerated uniformly by the hot spot pressure. This reduces the transfer of implosion kinetic energy to internal energy of the central hot spot, thus reducing the neutron yield. Furthermore, synthetic gated x-ray images of the hot spot self-emission indicate that P(4) shapes may be unquantifiable for DT layered capsules. Instead the positive P(4) asymmetry "aliases" itself as an oblate P(2) in the x-ray images. Correction of this apparent P(2) distortion can further distort the implosion while creating a round x-ray image. Long wavelength asymmetries may be playing a significant role in the observed yield reduction of NIF DT implosions relative to detailed postshot two-dimensional simulations.

Assembly of high-areal-density deuterium-tritium fuel from indirectly driven cryogenic implosions

The National Ignition Facility has been used to compress deuterium-tritium to an average areal density of ~1.0±0.1 g cm(-2), which is 67% of the ignition requirement. These conditions were obtained using 192 laser beams with total energy of 1-1.6 MJ and peak power up to 420 TW to create a hohlraum drive with a shaped power profile, peaking at a soft x-ray radiation temperature of 275-300 eV. This pulse delivered a series of shocks that compressed a capsule containing cryogenic deuterium-tritium to a radius of 25-35 μm. Neutron images of the implosion were used to estimate a fuel density of 500-800 g cm(-3).

Pressure stabilization of proteins from extreme thermophiles

We describe the stabilization by pressure of enzymes, including a hydrogenase from Methanococcus jannaschii, an extremely thermophilic deep-sea methanogen. This is the first published report of proteins from thermophiles being stabilized by pressure. Inactivation studies of partially purified hydrogenases from an extreme thermophile (Methanococcus igneus), a moderate thermophile (Methanococcus thermolithotrophicus), and a mesophile (Methanococcus maripaludis), all from shallow marine sites, show that pressure stabilization is not unique to enzymes isolated from high-pressure environments. These studies suggest that pressure stabilization of an enzyme may be related to its thermophilicity. Further experiments comparing the effects of increased pressure on the stability of alpha-glucosidases from the hyperthermophile Pyrococcus furiosus and Saccharomyces cerevisiae support this possibility. We have also examined pressure effects on several highly homologous glyceraldehyde-3-phosphate dehydrogenases from mesophilic and thermophilic sources and a rubredoxin from P. furiosus. The results suggest that hydrophobic interactions, which have been implicated in the stabilization of many thermophilic proteins, contribute to the pressure stabilization of enzymes from thermophiles.

Pressure-enhanced activity and stability of a hyperthermophilic protease from a deep-sea methanogen

We describe the properties of a hyperthermophilic, barophilic protease from Methanococcus jannaschii, an extremely thermophilic deep-sea methanogen. This enzyme is the first protease to be isolated from an organism adapted to a high-pressure-high-temperature environment. The partially purified enzyme has a molecular mass of 29 kDa and a narrow substrate specificity with strong preference for leucine at the P1 site of polypeptide substrates. Enzyme activity increased up to 116(deg)C and was measured up to 130(deg)C, one of the highest temperatures reported for the function of any enzyme. In addition, enzyme activity and thermostability increased with pressure: raising the pressure to 500 atm increased the reaction rate at 125(deg)C 3.4-fold and the thermostability 2.7-fold. Spin labeling of the active-site serine revealed that the active-site geometry of the M. jannaschii protease is not grossly different from that of several mesophilic proteases; however, the active-site structure may be relatively rigid at moderate temperatures. The barophilic and thermophilic behavior of the enzyme is consistent with the barophilic growth of M. jannaschii observed previously (J. F. Miller et al., Appl. Environ. Microbiol. 54:3039-3042, 1988).

Effects of hyperbaric pressure on a deep-sea archaebacterium in stainless steel and glass-lined vessels

The effects of hyperbaric helium pressures on the growth and metabolism of the deep-sea isolate ES4 were investigated. In a stainless steel reactor, cell growth was completely inhibited but metabolic gas production was observed. From 85 to 100 degrees C, CO(2) production proceeded two to three times faster at 500 atm (1 atm = 101.29 kPa) than at 8 atm. At 105 degrees C, no CO(2) was produced until the pressure was increased to 500 atm. Hydrogen and H(2)S were also produced biotically but were not quantifiable at pressures above 8 atm because of the high concentration of helium. In a glass-lined vessel, growth occurred but the growth rate was not accelerated by pressure. In most cases at temperatures below 100 degrees C, the growth rate was lower at elevated pressures; at 100 degrees C, the growth rates at 8, 250, and 500 atm were nearly identical. Unlike in the stainless steel vessel, CO(2) production was exponential during growth and continued for only a short time after growth. In addition, relatively little H(2) was produced in the glass-lined vessel, and there was no growth or gas production at 105 degrees C at any pressure. The behavior of ES4 as a function of temperature and pressure was thus very sensitive to the experimental conditions.

Quantitation of bleeding symptoms in children with von Willebrand disease: use of a standardized pediatric bleeding questionnaire

SUMMARY BACKGROUND

Excessive bruising and mucocutaneous bleeding are frequent presenting symptoms in childhood. A detailed bleeding history can distinguish children who may have an inherited bleeding disorder from those who are normal. There is a lack of standardization of such history taking in pediatric practise.

OBJECTIVES

To assess the performance of a Pediatric Bleeding Questionnaire (PBQ), an adaptation of a standardized adult bleeding questionnaire and score that includes pediatric-specific bleeding symptoms, in a cohort of children with von Willebrand disease (VWD).

PATIENTS/METHODS

Bleeding scores were determined by interview, for children with a previous diagnosis of VWD and a control group of unaffected siblings.

RESULTS

Bleeding scores were obtained for 100 children with VWD, median age 10.9 years (range, 0.8-17.8 years), and 21 unaffected siblings. Median bleeding score in children with VWD was 7.0 (range, 0-29) and in the control group was 0 (range, -1-2). Bleeding score varied within and between each VWD type: definite type 1, n = 40, median, 9.0 (range, 2-18); possible type 1, n = 38, median, 2.0 (0-15); type 2, n = 6, median, 14.0 (3-17); and type 3, n = 16, median, 12.0 (4-29). Bleeding scores in affected children correlated with age (Spearman's correlation coefficient, 0.35; P = 0.0004). The most frequent clinically significant bleeding symptoms were surgical bleeding, bleeding after tooth extraction and menorrhagia. Post-circumcision bleeding, cephalohematoma, macroscopic hematuria and umbilical stump bleeding were clinically significant in 32% (of circumcised males), 4%, 4% and 3% of children, respectively.

CONCLUSIONS

The PBQ provides a standardized quantitation of bleeding severity in children with VWD.

Active-site titration of serine proteases in organic solvents

Calculation of kinetic constants of an enzymatic reaction in organic solvents requires knowledge of the functional active-site concentration in organic solvents, and this can be significantly different than that in water. An experimental method for active-site titration of serine proteases in organic media has been developed based on the kinetics of inhibition by phenylmethanesulfonyl fluoride (PMSF), a serine-specific inhibitor (or suicide substrate). This kinetic approach is fundamentally different from other techniques that require complete titration of all accessible enzyme active sites. This active site titration method was applied to subtilisins BPN' and Carlsberg and alpha-chymotrypsin and resulted in fractions of active sites that ranged from 8 to 62% (of the fraction active in water) depending on the enzyme, the method of enzyme preparation, and the organic solvent used. The active-site concentration of subtilisin BPN' and Carlsberg increased with increasing hydrophobicity of the solvent and with increasing solvent hydration in tetrahydrofuran. The dependence of the fraction of active sites on the nature of the organic solvent appears to be governed largely by solvent-induced inactivation caused by direct interaction of a hydrophilic solvent with the enzyme.

Examination of primary metabolic pathways in a murine hybridoma with carbon-13 nuclear magnetic resonance spectroscopy

Primary metabolism of a murine hybridoma was probed with (13)C nuclear magnetic resonance (NMR) spectroscopy. Cells cultured in a hollow fiber bioreactor were serially infused with [1-(13)C] glucose, [2-(13)C] glucose, and [3-(13)C] glutamine. In vivo spectroscopy of the culture was used in conjunction with off-line spectroscopy of the medium to determine the intracellular concentration of several metabolic intermediates and to determine fluxes for primary metabolic pathways. Intracellular concentrations of pyruvate and alanine were very high relative to levels observed in normal quiescent mammalian cells. Estimates made from labeling patterns in lactate indicate that 76% of pyruvate is derived directly from glycolysis; some is also derived from the malate shunt, the pyruvate/melate shuttle associated with lipid synthesis and the pentose phosphate pathway. The rate of formation of pyruvate from the pentose phosphate pathway was estimated to be 4% of that from glycolysis; This value is a lower limit and the actual value may be higher. Incorporation of pyruvate into the tricarboxylic acid (TCA) cycle appears to occur through only pyruvate dehydrogenase; no pyruvate carboxylase activity was detected. The malate shunt rate was approximately equal to the rate of glutamine uptake. The rate of incorporation of glucosederived acetyl-CoA into lipids was 4% of the glucose uptake rate. The TCA cycle rate between isocitrate and alpha-ketoglutarate was 110% of the glutamine uptake rate.

Papain kinetics in the presence of a water-miscible organic solvent

The effects of various concentrations of a water-miscible organic solvent [a 7:3 (v/v) mixture of N, N dimethylformamide and dimethylsulfoxide] on the kinetics of papain have been investigated. The parameters k(cat) and K(m) for the amidase and esterase activity of papain using N-alpha-benzoyl-DL-arginine-p-nitroanilide (BAPNA) and N-alpha-benzoyl-L-arginine ethyl ester (BAEE) as substrates were determined. For both types of activity, k(cat) initially increased (up to about 15% solvent), and then decreased with increasing concentrations of organic solvent. In contrast, K(m) increased sharply with the organic solvent concentration. Active site titration at 0 and 50% solvent indicated no change in the amount of active enzyme. Fluorometric measurements of the emission spectrum of papain did not indicate any major conformational changes with increasing concentrations of organic solvent.

Regulation of interferon-stimulated genes in peripheral blood leukocytes in pregnant and bred, nonpregnant dairy cows

In ruminants, pregnancy results in up-regulation of a large number of IFN-stimulated genes (ISG) in the uterus. Recently, one of these genes was also shown to increase in peripheral blood leukocytes (PBL) during early pregnancy in sheep. Our working hypothesis is that conceptus signaling activates maternal gene expression in PBL in dairy cattle. The objectives of this study were to characterize ISG expression in PBL from pregnant (n = 20) and bred, nonpregnant (n = 30) dairy cows. Steady-state levels of mRNA for Mx1, Mx2, beta2-microglobulin, ISG-15, IFN regulatory factor-1, and IFN regulatory factor-2 were quantified. Holstein cows were synchronized to estrus and artificially inseminated (d 0). Blood samples were collected (coccygeal venipuncture) on d 0 and 16, 18, and 20 d after insemination for progesterone analysis and PBL isolation. Pregnancy was confirmed by transrectal ultrasonography at approximately 40 d after breeding. A status x day interaction was detected for Mx1, Mx2, and ISG-15 gene expression. When analyzed within day, levels of mRNA for ISG-15 and Mx1 were greater in pregnant compared with bred, nonpregnant cows on d 18 and 20, respectively. Expression of the Mx2 gene increased in the pregnant group compared with bred, nonpregnant cows on d 16, 18, and 20 after insemination. beta2-Microglobulin, IFN regulatory factor-1, and IFN regulatory factor-2 were not different between groups. The results clearly indicated that components of the innate immune response are activated in PBL during the period of pregnancy recognition and early embryo signaling. The physiological implications of these changes on maternal immune function are as yet unknown; however, they do provide a unique opportunity to identify bred, nonpregnant, cows 18 d after insemination in dairy cattle.

Dosage effect of minor arginyl- and isoleucyl-tRNAs on protein synthesis in an Escherichia coli in vitro coupled transcription/translation system

In Escherichia coli mRNA, the arginine codons AGA/AGG and the isoleucine codon AUA are rarely used with frequencies of about 0.35% and 0.41%, respectively. Six genes with a different number of these codons were expressed in an E. coli in vitro coupled transcription/translation system, which contained either tRNA prepared from E. coli cells carrying a plasmid with argU and ileX genes encoding rare tRNAs (tRNA(arg)(AGA/AGG) and tRNA(ile)(AUA)), designated codon-plus tRNA, or normal tRNA from cells lacking the plasmid. Genes having a low number of the rare codons, such as genes encoding chloramphenicol acetyltransferase and anti-gp120 single-chain Fv (artificially constructed to remove rare codons), were expressed at similar levels using with both tRNA preparations. On the other hand, the use of codon-plus tRNA increased the expression levels of genes having a relatively large number of the rare codons, including genes encoding archaeal proteins, green fluorescent protein of jelly fish origin, and a single-chain Fv of mouse origin, by about 20% higher than that using normal tRNA.

Nickel accumulation and nickel oxalate precipitation by Aspergillus niger

A strain of Aspergillus niger isolated from a metal-contaminated soil was able to grow in the presence of cadmium, chromium, cobalt, copper, and unusually high levels of nickel on solid (8.0 mM) and in liquid (6.5 mM) media. This fungus removed >98% of the nickel from liquid medium after 100 h of growth but did not remove the other metals, as determined by inductively coupled plasma spectroscopy. Experiments with non-growing, live fungal biomass showed that nickel removal was not due to biosorption alone, as little nickel was bound to the biomass at the pH values tested. Furthermore, when the protonophore carbonyl cyanide p-(trifluoremetoxy) phenyl hydrazone (FCCP) was added to the actively growing fungus nickel removal was inhibited, supporting the hypothesis that energy metabolism is essential for metal removal. Analytical electron microscopy of thin-sectioned fungal biomass revealed that metal removed from the broth was localized in the form of small rectangular crystals associated with the cell walls and also inside the cell. X-ray and electron diffraction analysis showed that these crystals were nickel oxalate dihydrate.

Uranyl precipitation by biomass from an enhanced biological phosphorus removal reactor

Heavy metal and radionuclide contamination presents a significant environmental problem worldwide. Precipitation of heavy metals on membranes of cells that secrete phosphate has been shown to be an effective method of reducing the volume of these wastes, thus reducing the cost of disposal. A consortium of organisms, some of which secrete large quantities of phosphate, was enriched in a laboratory-scale sequencing batch reactor performing Enhanced Biological Phosphorus Removal, a treatment process widely used for removing phosphorus. Organisms collected after the aerobic phase of this process secreted phosphate and precipitated greater than 98% of the uranyl from a 1.5 mM uranyl nitrate solution when supplemented with an organic acid as a carbon source under anaerobic conditions. Transmission electron microscopy, energy dispersive x-ray spectroscopy, and fluorescence spectroscopy were used to identify the precipitate as membrane-associated uranyl phosphate, UO2HPO4.

Torsades de pointes associated with high dose levomethadyl acetate (ORLAAM)

A patient undergoing management of heroin dependency with high dosages of the long-acting methadone derivative, levomethadyl acetate HCl (LAAM; ORLAAM) developed a prolonged QTc interval and polymorphic QRS complexes on EKG consistent with torsades de pointes (TdP). The patient was taking other drugs known to prolong the QTc interval (fluoxetine and IV cocaine), and those known to antagonize the activity of the P450 enzymes responsible for the metabolism of LAAM and its active metabolite (fluoxetine, cocaine and marijuana). No previous reports have appeared in the literature attributing this adverse event to LAAM therapy; however, five similar cases have been reported to the manufacturer. Animal studies indicate that LAAM and metabolites prolong the action potential duration of myocardial cells. We propose that predisposed patients on high doses of LAAM may be at risk for developing TdP. Patients being treated with LAAM should receive dosages consistent with guidelines and be evaluated for concomitant diseases, interacting drug therapies, and EKG abnormalities.

Analysis of an engineered sulfate reduction pathway and cadmium precipitation on the cell surface

We previously have genetically engineered an aerobic sulfate reduction pathway in Escherichia coli for the generation of hydrogen sulfide and demonstrated the pathway's utility in the precipitation of cadmium. To engineer the pathway, the assimilatory sulfate reduction pathway was modified so that cysteine was overproduced. Excess cysteine was then converted by cysteine desulfhydrase to an abundance of hydrogen sulfide, which then reacted with aqueous cadmium to form cadmium sulfide. In this study, observations of various E. coli clones were combined with an analysis of kinetic and transport phenomena. This analysis revealed that cysteine production is the rate-limiting step in the engineered pathway and provided an explanation for the phenomenon of cell surface precipitation. An analytical model showed that cadmium sulfide must form at the cell surface because the rate of cadmium sulfide formation is extremely fast and the rate of sulfide transport is relatively slow.

Towards more active biocatalysts in organic media: increasing the activity of salt-activated enzymes

The activation of freeze-dried subtilisin Carlsberg (SC) in hexane has been systematically studied and partially optimized with respect to the freezing method, the addition of inorganic salts and lyoprotectants, the initial concentration and final weight percent of additives, and the amount of water added to the organic solvent. Activity and water content were found to correlate directly with the kosmotropicity of the activating salt (kosmotropic salts bind water molecules strongly relative to the strength of water-water interactions in bulk solution). Combinations of kosmotropic salts with known lyoprotectants such as poly(ethylene glycol) (PEG) and sugars did not yield an appreciably more active catalyst. However, the combination of the kosmotropic sodium acetate with the strongly buffering sodium carbonate activated the enzyme more than the individual additives alone. Enzyme activity was enhanced further by the addition of small amounts of water to the organic solvent. Under optimal conditions, enzyme activity in hexane was improved over 27,000-fold relative to the salt-free enzyme, reaching a catalytic efficiency that was within one order of magnitude of k(cat)/K(m) for hydrolysis of the same substrate in aqueous buffer. Further activation to attain even higher catalytic efficiencies may be possible with additional optimization.

Mechanism of pressure-induced thermostabilization of proteins: studies of glutamate dehydrogenases from the hyperthermophile Thermococcus litoralis

In this study, we investigated the effect of pressure on protein structure and stability at high temperature. Thermoinactivation experiments at 5 and 500 atm were performed using the wild-type (WT) enzyme and two single mutants (D167T and T138E) of the glutamate dehydrogenase (GDH) from the hyperthermophile Thermococcus litoralis. All three GDHs were stabilized, although to different degrees, by the application of 500 atm. Interestingly, the degree of pressure stabilization correlated with GDH stability as well as the magnitude of electrostatic repulsion created by residues at positions 138 and 167. Thermoinactivation experiments also were performed in the presence of trehalose. Addition of the sugar stabilized all three GDHs; the degree of sugar-induced thermostabilization followed the same order as pressure stabilization. Previous studies suggested a mechanism whereby the enzyme adopts a more compact and rigid structure and volume fluctuations away from the native state are diminished under pressure. The present results on the three GDHs allowed us to further confirm and refine the proposed mechanism for pressure-induced thermostabilization. In particular, we propose that pressure stabilizes against thermoinactivation by shifting the equilibrium between conformational substates of the GDH hexamer, thus inhibiting irreversible aggregation.

Chemical denaturation and elevated folding temperatures are required for wild-type activity and stability of recombinant Methanococcus jannaschii 20S proteasome

The 20S proteasome from the extreme thermophile Methanococcus jannaschii (Mj) was purified and sequenced to facilitate production of the recombinant proteasome in E. coli. The recombinant proteasome remained in solution at a purity level of 80-85% (according to SDS PAGE) following incubation of cell lysates at 70 degrees C. Temperature-activity profiles indicated that the temperature optima of the wild-type and recombinant enzymes differed substantially, with optimal activities occurring at 119 degrees C and 95 degrees C, respectively. To ameliorate this discrepancy, two recombinant enzyme preparations were produced, each of which included denaturation of the proteasome by 4 M urea followed by high-temperature (85 degrees C) dialysis. The wild-type temperature optimum was restored, but only if proteasome subunits were denatured and refolded prior to assembly (a preparation designated as alpha & beta). In contrast, when proteasome assembly preceded denaturation (designated alpha + beta) the optimum temperature was raised to a lesser degree. Moreover, the alpha & beta and alpha + beta preparations had apparent thermal half-lives at 114 degrees C of 54.2 and 26.2 min, respectively, and the thermostability of the less stable enzyme was more sensitive to a reduction in pH. Attainment of wild-type activity and stability thus required the proper folding of both the alpha- and beta-subunits prior to proteasome assembly. Consistent with this behavior, dual-scanning calorimetry (DSC) measurements revealed differences in the reassembly efficiency of the two proteasome preparations. The ability to produce structural conformers with dramatically different thermal optima and thermostabilities may facilitate the determination of molecular forces and structural motifs responsible for enzyme thermostablity and high-temperature activity.