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Quantum technologies rely on the ability to coherently transfer information encoded in quantum states along quantum channels. Decoherence induced by the environment sets limits on the efficiency of any quantum-enhanced protocol. Generally, the longer a quantum channel is the worse its capacity is. We show that for non-Markovian quantum channels this is not always true: surprisingly the capacity of a longer channel can be greater than of a shorter one. We introduce a general theoretical framework linking non-Markovianity to the capacities of quantum channels and demonstrate how harnessing non-Markovianity may improve the efficiency of quantum information processing and communication.

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We study the dynamics of quantum and classical correlations in the presence of nondissipative decoherence. We discover a class of initial states for which the quantum correlations, quantified by the quantum discord, are not destroyed by decoherence for times t<[symbol: see text]. In this initial time interval classical correlations decay. For t>[symbol: see text], on the other hand, classical correlations do not change in time and only quantum correlations are lost due to the interaction with the environment. Therefore, at the transition time [symbol: see text] the open system dynamics exhibits a sudden transition from classical to quantum decoherence regime.

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We demonstrate a scaling method for non-Markovian Monte Carlo wave-function simulations used to study open quantum systems weakly coupled to their environments. We derive a scaling equation, from which the result for the expectation values of arbitrary operators of interest can be calculated, all the quantities in the equation being easily obtainable from the scaled Monte Carlo wave-function simulations. In the optimal case, the scaling method can be used, within the weak coupling approximation, to reduce the size of the generated Monte Carlo ensemble by several orders of magnitude. Thus, the developed method allows faster simulations and makes it possible to solve the dynamics of the certain class of non-Markovian systems whose simulation would be otherwise too tedious because of the requirement for large computational resources.

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Reactive intermediate enzyme complexes are difficult to study directly and the use of physical methods requiring observation periods of more than a second has not been possible heretofore. Here we introduce a simple approach, the "Le Chatelier forcing method" which does for the first time produce significant concentrations of such kinetically competent central intermediates observable for extended periods of time. The method involves only the forcing of the accumulation of intermediate complexes at thermodynamic equilibrium by the use of high reactant concentrations working against a high concentration of a product, combined with a valid and applicable method of analysis. We demonstrate this approach using the glutamate dehydrogenase catalyzed reaction with the reaction product ammonia as a "dam" to oppose the forward driving force of NADP and l-glutamate. We demonstrate the accumulation of substantial amounts measurable amounts of stable enzyme-NADPH-alpha-carbinolamine and alpha-iminoglutarate complexes in three different alpha-amino acid dehydrogenases. We describe the manipulation of such Le Chatelier forced equilibria to increase the prominence of particular species and discuss the implications of these findings for previously unattainable experimental approaches.

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Hemothorax and persistent thoracic bleeding is frequently an indication for thoracotomy after trauma. Unfortunately, the source of the hemorrhage is often not identified. Presently, selective arteriography and transcatheter embolization (SATE) offers a good and safe alternative to localize and control hemorrhage from arterial injuries in selected patients. The records of eight patients who underwent SATE were reviewed. There were six blunt and two penetrating chest injuries. Four patients had significant preexisting medical comorbidities. Three patients with blunt injuries had undergone exploratory thoracotomy, but continued to bleed postoperatively. In three patients, angiography was indicated for associated thoracic and pelvic injuries, and five patients had SATE specifically due to thoracic hemorrhage. In all patients, SATE was effective to diagnose and control the hemorrhage. There were no complications related to the SATE procedure. Two patients died secondary to severe cerebral injuries. Given hemodynamic stability, SATE can be considered in patients who have already had a thoracotomy, have significant associated medical conditions, or those in need of other angiographic studies. Careful technique and a readiness to abandon SATE in unstable patients or when a suitable catheter position cannot be achieved are important technical points.

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A highly constrained and heavily overdetermined multiwavelength transient state kinetic approach has been used to study the oxidative deamination of L-glutamate catalyzed by beef liver glutamate dehydrogenase. Spectra generated using the known enzyme-reduced coenzyme-substrate spectrum served as models for deconvolution of kinetic scan data. Deconvolution of the multiwavelength time course array shows formation of three distinguishable intermediates in the reaction sequence, an ultrablue-shifted complex, an ultrared-shifted complex, and a blue-shifted complex. The ultrablue-shifted entity is identified as the enzyme-NADPH-alpha-iminoglutarate complex (ERI) and the ultrared as the enzyme-NADPH-alpha-carbinolamine complex (ERC). The blue-shifted complex is characterized as the E-NADPH-ketoglutarate species (ERK). The location of these species along the reaction coordinate has been determined and their kinetic competency in the reaction sequence has been established by fitting the concentration time courses of the components for both the alpha-deuterio- and the alpha-protio-L-glutamate reactions to the now highly constrained differential equations derived from a kinetic scheme involving the sequential formation of alpha-iminoglutarate, alpha-carbinolamine, and alpha-ketoglutarate-reduced coenzyme complexes, following the formation of two prehydride transfer complexes.

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BACKGROUND: Highly concentrated solutions of sulfuric acid are available to unclog drains. We have noted a substantial number of both accidental and intentional cutaneous burns caused by these agents. METHODS: A retrospective review was conducted of children and adults who sustained sulfuric acid burns over a 13-year period ending in May 1996. Reports of injuries related to drain cleaners filed with the United States Consumer Product Safety Commission between 1991 and 1995 were also reviewed. RESULTS: Twenty-one patients (13 children, 8 adults) sustained cutaneous burns caused by concentrated sulfuric acid solutions. In 8 instances, the burn was accidental, whereas in 13 cases, sulfuric acid was used as a weapon. Median total body surface area burned was 5% (range, 1-25%). Approximately 50% of burns involved the face and neck. Skin grafting was required in 14 patients (66%). It is estimated that nationwide approximately 3,000 injuries per year are related to drain cleaners and that one-third of these involve cutaneous burns. CONCLUSION: Highly concentrated sulfuric acid drain cleaner can produce full-thickness cutaneous burns that require skin grafting in the majority of cases. Proper use of these agents and sequestering them from children may reduce accidental contact; however, their abuse as agents of assault remains a source of significant morbidity.

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The effects of dichloroacetate (DCA) on fatty acid oxidation and flux through pyruvate dehydrogenase (PDH) were studied in ischemic, reperfused myocardium supplied with glucose, long-chain fatty acids, lactate, pyruvate, and acetoacetate. The oxidation rates of all substrates were determined by combined 13C nuclear magnetic resonance (NMR) spectroscopy and oxygen-consumption measurements, and PDH flux was assessed by lactate plus pyruvate oxidation. In nonischemic control hearts, DCA increased PDH flux more than eightfold (from 0.68 +/- 0.28 to 5.81 +/- 1.16 micromol/min/g dry weight; n = 8 each group; p < 0.05) and significantly inhibited the oxidation of acetoacetate and fatty acids. DCA also improved mechanical recovery after 30 min of ischemia plus 30 min of reperfusion but did not significantly increase PDH flux measured at the end of the reperfusion period (1.35 +/- 0.42 micromol/min/g dry weight) compared with untreated ischemic hearts (0.87 +/- 0.28 micromol/min/g dry weight; n = 8 each group; p = NS). Although DCA had a modest effect on functional recovery in the reperfused myocardium, this beneficial effect was not associated with either marked stimulation of PDH flux or inhibition of fatty acid oxidation.

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A multiwavelength transient-state kinetic study of the glutamate dehydrogenase catalyzed reaction has proven that an alpha-iminoglutarate complex is an observable intermediate in the reverse direction. It also shows the existence of two enzyme-NADPH-ketoglutarate complexes, only one of which reacts with ammonia rapidly.

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OBJECTIVES: A recent report (J Clin Invest 1993;92:831-9) found no effect of glutamate plus aspartate on metabolic pathways in the heart, but the experimental conditions did not model clinical cardioplegia. The purpose of this study was to determine the effects of glutamate and aspartate on metabolic pathways feeding the citric acid cycle during cardioplegic arrest in the presence of physiologic substrates. METHODS: Isolated rat hearts were supplied with fatty acids, lactate, pyruvate, glucose, and acetoacetate in physiologic concentrations. These substrates were enriched with 13C, which allowed a complete analysis of substrate oxidation by 13C-nuclear magnetic resonance spectroscopy in one experiment. Three groups of hearts were studied: arrest with potassium cardioplegic solution, arrest with cardioplegic solution supplemented with glutamate and aspartate (both in concentrations of 13 mmol/L), and a control group without cardioplegic arrest. RESULTS: In potassium-arrested hearts, the contributions of fatty acids and lactate to acetyl coenzyme A were reduced, and acetoacetate was the preferred substrate for oxidation in the citric acid cycle. The addition of aspartate and glutamate in the presence of cardioplegic arrest did not further alter patterns of substrate utilization substantially, although acetoacetate use was somewhat lower than with simple cardioplegic arrest. When [U-13C]glutamate (13 mmol/L) and [U-13C]aspartate (13 mmol/L) were supplied as the only compounds labeled with 13C, little enrichment in citric acid cycle intermediates could be detected. CONCLUSIONS: Glutamate and aspartate when added to potassium cardioplegic solutions have relatively minor effects on citric acid cycle metabolism.

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We have related the ratios of the protein fluorescence quenching and nucleotide absorbance time courses for the glutamate dehydrogenase catalyzed oxidative deamination of L-glutamate to identify the occurrence and sequential location of a previously demonstrated charge-transfer intermediate. Static studies showed the major portion of the fluorescence quenching signal to be due to radiationless singlet energy transfer from tryptophan to reduced coenzyme chromophores and that conformational changes contribute little to this signal. The ratio approach applied to the transient time courses shows correspondingly that, over most of the time range, the fluorescence quenching signal provides a quantitative measure of the sum of all posthydride transfer species. However, it also indicates the very early occurrence of a species of anomalous optical properties for the reaction catalyzed by the Clostridium symbiosum enzyme as well as that from bovine liver. Transient-state kinetic isotope effect time courses of both the fluorescence and the absorbance signals confirm that this species must be the prehydride charge-transfer complex in both enzyme reactions. Kinetic analysis of alpha-deuterio- and alpha-protio-L-glutamate reaction time courses proves the kinetic competence of the assignments. These results also demonstrate that the intramolecular transfer of a proton from the alpha-amino group of the substrate to an immediately adjacent aspartate carboxylate group on the enzyme is an obligatory initial event in the reactions catalyzed by both enzyme species, even though the occurrence of protein release from a critical lysine residue to the solvent occurs at different phases in those two reactions. The abnormally low intrinsic KIE required to simulate both the alpha-deuterio-L-glutamate reaction and its protio counterpart implies that the transition state of the hydride transfer step must be highly asymmetric.

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The objective of this study was to characterize the association between drug and alcohol intoxication at the time of injury and subsequent complications and mortality in hospitalized patients with burns. A computerized burn database was used to analyze data on 3047 consecutive adult (21 to 75 years) hospitalized patients with burns admitted between January 1982 and August 1994. Data for intoxicated (by history, blood alcohol content, or positive drug screen) and nonintoxicated patients were compared. The same analysis was also conducted on 429 consecutive adolescent patients with burns (ages 14 to 20 years) admitted during the same time period. The incidence of intoxication at the time of burn was 6.9%. No significant differences in age, sex, race, or burn size were noted. Intoxicated patients had a higher incidence of associated injuries. Skin graft loss, cellulitis, donor site conversion, hypotension, and pneumonia were more common in the intoxicated group. They also had more intensive care unit admissions, ventilator days, operations, transfusions, and total hospital days. Intoxicated patients had a lower mortality (7.1%) than patients in the control group (10.9%). Intoxication at the time of burn injury is an important predictor of complications in adult patients with burns.

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Glutamate dehydrogenase from beef liver (bl GDH) and the corresponding enzyme from Clostridium symbiosum (cs GDH) each catalyze the same sequence of chemical events in the oxidative deamination of L-glutamate. This catalysis involves interactions between at least six conserved functional groups, each of which appears to occupy the same geometric position with respect to the substrate molecule in both enzyme--coenzyme--L-glutamate reactive ternary complexes. In both cases steady-state V/K pH profiles indicate the requirement for the transfer to the solvent of a single proton from the same abnormal lysine for L-glutamate to bind and react; the pK of that lysine is the same for both enzymes. Here we report studies of the proton traffic between enzyme and solvent using direct pH-stat back-titration and indicator dye measurements on dead-end inhibitor ternary complexes, simultaneous transient-state time courses of proton and product, and transient-state kinetic isotope studies on both enzymes. We find that in the cs GDH catalyzed reaction the single proton is released only after the hydride transfer step whereas in the bl GDH reaction this proton release occurs prior to the hydride transfer step, despite the fact that the substrate molecule undergoes the same sequence of chemical events in both reactions. Interpreting these results in the context of the X-ray crystallographic structures of cs GDH and its NAD binary complex and of thermodynamic studies of bl GDH and its complexes, we conclude that the difference in the relative times of proton release in the two enzyme-catalyzed reactions must be ascribed to a difference in the sequence of active site cleft-opening and -closing events in the two identical reaction sequences. We suggest a possible biological significance to this unusual method of modulating a common reaction to suit differing metabolic roles.

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In previous transient state kinetic work from this laboratory, we proposed a new mechanism for the glutamate dehydrogenase-catalyzed oxidative deamination reaction involving an initial replacement of a proton from lysine 126 by a single bound water molecule, followed by closure of the active site cleft and expulsion of bulk water, providing a hydrophobic environment for the ensuing hydride transfer step. Here, we report the results of further transient state fluorescence, absorbance, and kinetic isotope effect studies, which demonstrate the occurrence of an unusual intermediate in the early steps of that reaction. This phenomenon is revealed by an initial fluorescence burst that occurs in the time period where the absorbance signal is still in its lag phase. Using an extension of the proton/product ratio approach we have described earlier, we show that this intermediate is a strongly fluorescent but weakly absorbing species whose absorption maximum is red-shifted beyond that of other known complexes of this enzyme. The transient state kinetic isotope effects of the fluorescence and absorbance signals are compatible only with a reaction scheme in which the formation of the fluorescent complex precedes the hydride transfer step. The optical properties of this enzyme-oxidized coenzyme-substrate intermediate strongly suggest that it is a charge-transfer complex, similar in nature to the complex responsible for the well known "Racker band" reported in 1952 for glyceraldehyde-3-phosphatase dehydrogenase (Racker, E., and Krimsky, I. (1952) Nature 169, 1043-1044). The crystal structure studies of the enzyme-coenzyme and enzyme-L-glutamate complexes of the closely analogous Clostridium symbosium glutamate dehydrogenase, reported by the Sheffield group (Stillman, T. J., Baker, P. J., Britton, K. L., and Rice, D. W. (1993) J. Mol. Biol. 234, 1131-1139), provide a basis for a physical explanation of the phenomenon. We conclude that the charge transfer phenomenon is caused by the near apposition of the unprotonated alpha-amino group of the substrate in a form of the enzyme in which a conformational change has caused the complete closing of the active site cleft.

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We have previously characterized the thermodynamic relationships which govern the dissociation of NADPH from bovine liver glutamate dehydrogenase and the allosteric control of that mechanically and physiologically important process by a variety of effectors. We have found that the cooperative occupancy of a specific anion binding, while the occupancy of a second allosteric acetate binding site disrupts that anion binding site and opposes those effects (Singh & Fisher, 1994). We report here the results of transient-state studies on the kinetics of the various processes involved in this complex equilibrium. We find that the only intrinsically slow steps are those of NADPH binding and dissociation, that the complex kinetic behavior of the overall system is due solely to very rapid equilibrium binding processes involving phosphate, acetate, and hydrogen ions, and that these ions exert their various effects on the kinetics of the binding process by altering the equilibrium concentrations of the two kinetically significant reactive species, E and E-NADPH. The slow intrinsic rates of NADPH association and dissociation are ascribed to a ligand-induced conformational change involving a major alteration in the degree of closure of the enzyme's active-site cleft.

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We introduce a novel transient-state kinetic approach which can resolve proton and product time courses into a series of individual steps that comprise the reaction path. We have applied this approach to the oxidative deamination reaction catalyzed by bovine liver glutamate dehydrogenase, measuring both the product (NADPH) and proton time courses at various pH values. The global treatment (over all pH values) resolves the very early portion of this reaction quantitatively and provides a continuous time course for each of the six protonic species. We propose the following mechanism: L-glutamate binds to an open conformation of the enzyme-NADP complex, forming salt bridges between its alpha- and gamma-carboxyl groups and the protonated forms of enzyme lysine residues 114 and 90, respectively. In this position, the alpha-H atom of the substrate is too far from the nicotinamide ring for hydride transfer to occur. In the next step, three events occur in a concerted manner: lysine 126 loses a proton and acquires a single water molecule; the active site cleft closes; bulk water is expelled; the substrate and coenzyme are forced closer together and remain in a nonaqueous environment during the ensuing chemical events, returning to an open conformation only in time to allow the product release steps to occur. Thus, substrate binding accomplishes a number of important tasks which are themselves an integral part of the catalytic mechanism. Combining the novel transient state approach developed here with steady-state kinetic information can produce a detailed mechanistic resolution of otherwise hidden steps.

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We have used the stopped-flow indicator dye method to measure proton release and product formation simultaneously in the initial transient-state portion of the glutamate dehydrogenase-catalyzed oxidative deamination of L-glutamate. We observe a measurably slow release of a proton from the enzyme-NADP-L-glutamate complex. This proton release precedes the hydride transfer step, as indicated by the distinct lag in the product formation signal. We show that the proton release step corresponds to an obligatory intermediate in the reaction sequence. We also find that compounds which are competitive inhibitors of L-glutamate are capable of inducing this phenomenon. We prove that this unanticipated prehydride transfer event cannot be due to the release of an alpha-amino group proton from the substrate.

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The usefulness of the indicator dye method for the detection of transient enzyme-product intermediates has been very limited due to the near impossibility of resolving the apparent single exponential time courses resulting from sequences of steps linked by rather similar rate constants. We propose here a novel approach, the proton-product time course method, a procedure which can extract a great deal of the mechanistic information which remains buried in conventional proton release-time course measurements. The method involves nothing more than measuring the ratio, r, of the moles of H+ released to the moles of product formed as a function of time. We derive the theory relating this r function to mechanisms of varying complexity, explore the theoretical behavior of the function in various possible mechanistic situations, and employ the new approach in an experimental system. We demonstrate the fact that the proton/product time course ratio method can provide evidence of the existence of hidden steps in transient state kinetic studies, that it can determine accurate thermodynamic pK values of the intermediate complexes involved in those steps, and that it can produce time courses of individual intermediates which are obscure to conventional kinetic methods.

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The nature of a general anion binding site that regulates NADPH binding to L-glutamate dehydrogenase has been explored. Dissociation constants for the enzyme-NADPH complex were measured by difference spectroscopy in the presence of phosphate, pyrophosphate, ADP and acetate ions. Whereas two molecules of phosphate, binding in a cooperative fashion, raise the Kd of the enzyme-NADPH complex 50-fold from 2.3 microM, a single pyrophosphate raises the Kd only 23-fold, disproving the notion that the anion binding site is simply the pyrophosphate binding site of NADPH. ADP raises the Kd of the enzyme-NADPH complex 2-fold for a given phosphate concentration, and formation of the enzyme-ADP complex is itself interfered with by phosphate and pyrophosphate, indicating that these anions interact with the same anion binding site. Acetate ion acts in a manner opposite to that of phosphate, pyrophosphate and ADP and reverses the weakening effect that these ions exert on NADPH binding, returning the Kd of the enzyme-NADPH complex to 2.3 microM. In the absence of these anions, however, acetate exerts no measurable effect on the Kd, suggesting an allosteric mechanism.

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Functional group interactions involved in the formation of the glutamate dehydrogenase-NADPH binary complex have been studied by three independent but complementary approaches: the pH dependence of the overall dissociation constant measured by an improved differential spectroscopic technique; the pH dependence of the enthalpy of complex formation measured by flow calorimetry; and the pH dependence of the number of protons released to, or taken up from, the solvent in the complex formation reaction, measured by titration. We conclude that the coenzyme binds to the enzyme through three distinguishable interactions: a pH-independent process involving the binding of the reduced nicotinamide ring; a relatively weak "proton-stabilizing" process, occurring at low pH involving the shift at a pK of 6.3 in the free enzyme to 7.0 in the enzyme-NADPH complex; and a stronger "proton-destabilizing" process, occurring at a higher pH involving a shift of a pK of 8.5 in the enzyme down to 6.9 in the enzyme-NADPH complex. The proton ionization of the free enzyme involved in this third interaction exhibits some unusual thermodynamic parameters, having delta Go = +11.5 +/- 0.1 kcal mol-1, delta Ho = +19 +/- 1 kcal mol-1, and delta So = +23 eu. We show here that this proton ionization step is directly related to and indeed constitutes the "implicit" shift in enzyme macrostates which we have shown to be responsible for the existence of large highly nonlinear delta Cpo effects in the formation of this complex [Fisher, H. F., Colen, A. H., & Medary, R. T. (1981) Nature (London) 292, 271-272].

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