Enhancement of Stability in n-Channel OFETs by Modulating Polymeric Dielectric

In this study, a high-K material, aluminum oxide (AlO_x), as the dielectric of organic field-effect transistors (OFETs) was used to reduce the threshold and operating voltages, while focusing on achieving high-electrical-stability OFETs and retention in OFET-based memory devices. To achieve this, we modified the gate dielectric of OFETs using polyimide (PI) with different solid contents to tune the properties and reduce the trap state density of the gate dielectric, leading to controllable stability in the N, N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C₁₃)-based OFETs. Thus, gate field-induced stress can be compensated for by the carriers accumulated due to the dipole field created by electric dipoles within the PI layer, thereby improving the OFET's performance and stability. Moreover, if the OFET is modified by PI with different solid contents, it can operate more stably under fixed gate bias stress over time than the device with AlO_x as the dielectric layer only can. Furthermore, the OFET-based memory devices with PI film showed good memory retention and durability. In summary, we successfully fabricated a low-voltage operating and stable OFET and an organic memory device in which the memory window has potential for industrial production.

Ultraviolet Light-Activated Charge Modulation Heterojunction for Versatile Organic Thin Film Transistors

Organic thin film transistors (OTFTs) are a promising technology for the application of photosensors in smart wearable devices. Light-induced electrical behavior of OTFTs is explored to achieve diverse functional requirements. In most studies, OTFTs show an increased drain current (I_D) under light irradiation. Here, we use an ultraviolet (UV) light absorption top layer, tris(8-hydroxyquinoline) aluminum (Alq3), to improve the UV light response of poly(3-hexylthiophene-2,5-diyl) (P3HT)-based OTFTs. Unexpectedly, the Alq3-covered device operated at the accumulation mode demonstrates a decreased I_D during the UV light irradiation. N,N'-Ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI, electron acceptor), pentacene (electron donor), and lithium fluoride (LiF, insulator) as an interlayer were inserted between the P3HT and the Alq3 layers. The PTCDI/Alq3-covered device also shows an unusual decrease in I_D under the UV light but an increase in I_D under the green light. The pentacene/Alq3-covered device shows an increased I_D during the UV light irradiation and, unexpectedly, a memory effect in I_D after removing the UV light. The LiF/Alq3-covered device exhibits an electrical behavior similar to the bare P3HT-based device under the UV light. Results of spectroscopic analyses and theoretical calculations have shown that the occurrence of charge transfer at heterojunctions during the UV light irradiation causes charge modulation in the multilayered P3HT-based OTFTs and then results in an unusual decrease or memory effect in I_D. In addition, the unexpected I_D reduction can be observed in the Alq3-covered poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene]-based OTFTs under UV light. The features, including opposite electrical responses to different wavelengths of light and optical memory effect, provide the multilayered P3HT-based OTFTs with potential for various optical applications, such as image recognition devices, optical logic gates, light dosimeters, and optical synapses.

Ferromagnetism above Room Temperature in a Ni-Doped Organic-Based Magnetic Semiconductor

Ferromagnetic semiconductors with structural flexibility are an indispensable feature for future flexible spin-electronic applications. In this case, we introduce magnetic ingredients into an organic semiconductor, namely, pentacene, to form a ferromagnetic organic semiconductor (FOS). The first observation for ferromagnetic Ni-doped pentacene semiconductors at room temperature in the field of semiconductor spintronics is reported in this article. To date, the mechanism of FOSs with ferromagnetism is not understood yet, especially when their Curie temperature is enhanced above room temperature. Here, we demonstrate dopants of Ni atoms and the modulation of the growth temperature in the FOS films to achieve room-temperature ferromagnetic properties in a series of FOS films, one of which has a maximum coercivity of 257.6 Oe. The spin-exchange interaction between a Ni atom and a pentacene molecule is detected through the magnetic hysteresis obtained using a superconducting quantum interference device magnetometer. We verify the effectiveness of this spin coupling through magnetic force microscopy, Raman spectroscopy, scanning Kelvin probe microscopy, and theoretical simulation. A model for the indirect spin coupling between Ni atoms is proposed for the mechanism of room-temperature ferromagnetic ordering of spins due to the exchange force indirectly. We believe that the π-electrons of pentacene molecules at the triple state for this model can support the spin coupling of electrons of Ni atoms. Our findings facilitate the development of brand-new spintronic devices with structural flexibility and room-temperature ferromagnetism.

Enhanced Functionality of Dual-Gate Organic Transistors Based on Semiconducting/Insulating Polyblend-Induced Asymmetric Charge Modulation Layers

Dual-gate organic thin-film transistors (DG-OTFTs) with enhanced functionality, including large current enhancement behavior, highly efficient threshold voltage controllability, and self-contained dual-mode logic gate features, are reported. These DG-OTFTs are based on a semiconducting/insulating polyblend-based active layer with asymmetric top and bottom charge modulation layers (atb-CMLs). The atb-CMLs are automatically generated through the preparation of multilayer stacks of phase-separated semiconducting poly(3-hexylthiophene) (P3HT):insulating poly(methylmethacrylate) (PMMA) polyblend layer, poly(vinylidene fluoride) (PVDF) layer, and cross-linked-poly(4-vinylphenol) (cPVP) layer. They consist of a thin PMMA bottom layer and an uneven-shaped PMMA:PVDF miscible mixture-based top layer. The presence of the polarizable insulating PMMA, PVDF, and PMMA:PVDF mixture regions causes the bottom and top CMLs to experience electrical polarization, which induces the dipole field to achieve efficient charge modulation functions in DG-OTFTs. Owing to the presence of atb-CMLs, the DG-OTFTs exhibit unprecedented electrical characteristics, such as the easy depletion of the bottom channel by the top gate potential. However, the top channel can work properly only when given a bottom gate potential (either positive or negative). Given these unusual electrical features, the design of the fundamental dual-mode logic gates (e.g., AND and OR gates) can be achieved with just one DG transistor. This finding opens an interesting direction for the preparation of DG-OTFTs with diverse operating modes and increasing functionality, thereby widening the application potential of such transistors.

Alendronate medication possession ratio and the risk of second hip fracture: an 11-year population-based cohort study in Taiwan

Alendronate is effective in preventing second hip fracture in osteoporotic patients. However, no consensus exists on the duration that is effective in preventing a second hip fracture. Our study demonstrated that risk can be reduced when the prescription is ≥ 6 months for the year following the index hip fracture.

INTRODUCTION

Alendronate is effective in preventing second hip fracture in osteoporotic patients. However, no consensus exists on the accurate medication possession ratio (MPR) that is effective in preventing a second hip fracture. Our objective was to compare the risk of second hip fracture in patients treated with different MPR of alendronate.

METHODS

In this population-based cohort study, data from National Health Insurance Research Database of Taiwan were analyzed. Patients 50 years and older who had an index hip fracture and were not receiving any osteoporotic medications before their fracture during 2000-2010 were included. The cohort consisted of 88,320 patients who were new alendronate users (n = 9278) and non-users (n = 79,042). Those without alendronate were matched 4:1 as the control group. Patients were subdivided into those with no medication, MPR < 25%, MPR 25-50%, MPR 50-75%, and MPR 75-100%. Cox proportional hazard models were used to calculate the adjusted hazard ratios for different MPRs of alendronate.

RESULTS

After matching, 38,675 patients were included in this study; 20,363 (52.7%) were women, and 30,940 (80%) patients were without medication of alendronate. During follow-up on December 31, 2012, 2392 patients had a second hip fracture, for an incidence of 1449/100,000 person-years. Patients with alendronate MPR 50-75% had a lower risk of a second hip fracture compared to non-users (hazard ratio 0.66). When the MPR increased to 75-100%, the hazard ratio decreased to 0.61.

CONCLUSIONS

In this population-based cohort study, risk of a second hip fracture can be reduced when the alendronate MPR is ≥ 50% for the year following the index hip fracture. As the MPR increases, the risk of a second hip fracture decreases.

Electronic structure manipulation of graphene dots for effective hydrogen evolution from photocatalytic water decomposition

This paper presents a heteroatom doping strategy to manipulate the structure of graphene-based photocatalysts for effective hydrogen production from aqueous solution. Oxygenation of graphene creates a bandgap to produce semiconducting graphene oxide, nitrogen doping extends the resonant π-conjugation to prolong the charge lifetime, and sulfur doping breaks the electron neutrality to facilitate charge transfer. Accordingly, ammonia-treated sulfur-nitrogen-co-doped graphene oxide dots (A-SNGODs) are synthesized by annealing graphene oxide sheets in sulfur-ammonia, oxidizing the sheets into dots, and then hydrothermally treating the dots in ammonia. The A-SNGODs exhibit a high nitrogen content in terms of quaternary and amide groups that are formed through sulfur-mediated reactions. The peripheral amide facilitates orbital conjugations to enhance the photocatalytic activity, whereas the quaternary nitrogen patches vacancy defects to improve stability. The simultaneous presence of electron-withdrawing S and electron-donating N atoms in the A-SNGODs facilitates charge separation and results in reactive electrons. When suspended in an aqueous triethanolamine solution, Pt-deposited A-SNGODs demonstrate a hydrogen-evolution quantum yield of 29% under monochromatic 420 nm irradiation. The A-SNGODs exhibit little activity decay under 6-day visible-light irradiation. This study demonstrates the excellence of the heteroatom-doping strategy in producing stable and active graphene-based materials for photoenergy conversion.

Controlling carrier trapping and relaxation with a dipole field in an organic field-effect device

A novel polyimide electret using as the gate dielectric layer and charge trapping layer of n-type organic transistors was synthesized to improve the memory effect and electrical stability.

Synergistic Effects of Binary-Solvent Annealing for Efficient Polymer-Fullerene Bulk Heterojunction Solar Cells

Conjugated polymer-fullerene-based bulk-heterojunction (BHJ) organic solar cells (OSCs) have attracted tremendous attention over the past two decades because of their potential to develop low-cost and easy methods to produce energy from light. The complicated microstructure and morphology with randomly organized architecture of these polymer-fullerene-based active layers (ALs) is a key factor that limits photovoltaic performance. In this study, a binary-solvent annealing (BSA) approach was established to improve the poly(3-hexylthiophene):indene-C60 bisadduct-based AL for efficient BHJ-type OSCs by varying the second solvents with different boiling points (BP). Thus, we were able to change the evaporation behavior of cosolvents and consequently obtain the various microstructural properties of the AL. An in-depth study was conducted on the solvent-evaporation driven morphology of the active layer under various cosolvent conditions and its effect on the photovoltaic parameters of OSCs. Under the BSA processes, we found that the specimens with low-BP second solvents allows us to observe a more ideal AL for increasing photon absorption and efficient charge transport and collection at the respective electrodes, resulting in enhanced PCE of the corresponding OSCs. By contrast, the specimens with high-BP second solvents exhibit random microstructures, which are detrimental to charge transport and collection and lead to diminished PCE of the corresponding OSCs. By appropriately selecting the composition of a binary solvent, BSA can be employed as an easy method for the effective manipulation of the microstructures of ALs. BSA is a promising technique for the performance enhancement of not only OSCs but also other organic/polymeric-based electronic devices.

Spontaneous Formation of an Ideal-Like Field-Effect Channel for Decay-Free Polymeric Thin-Film Transistors by Multiple-Scale Phase Separation

We demonstrate semiconducting polymer-based thin-film transistors (PTFTs) with fast switching performance and an uncommon nondecaying feature. These PTFTs based on widely studied poly(3-hexylthiophene) are developed by incorporating the insulating polymer into the active channel and subjecting the compound to specific, spontaneous multiple-scale phase separation (MSPS). An in-depth study is conducted on the interfacial and phase-separated microstructure of the semiconducting/insulating blending active layer and its effect on the electrical characteristics of PTFTs. The polyblends exhibit a confined crystallization behavior with continuously semiconducting crystalline domains between scattered insulator-rich domains. The insulator-rich domains can block leakage current and strengthen the gate control of the channel. A small amount of the insulating polymer penetrates the bottom of the active channel, resulting in effective interface modification. We show specific MSPS morphology of the present blending films to reduce charge trapping effects, enhance charge accumulation, and create a high-seed switching channel. The findings enable us to develop the required morphological conceptual model of the ideal-like field-effect-modulated polymer-based active channel. The polyblend-based PTFTs with MSPS morphology also have promising sensing functions. This study offers an effective approach for overcoming the major drawbacks (instability and poor switching) of PTFTs, thus allowing such transistors to have potential applications.

A nanoscale study of charge extraction in organic solar cells: the impact of interfacial molecular configurations

In the optimization of organic solar cells (OSCs), a key problem lies in the maximization of charge carriers from the active layer to the electrodes. Hence, this study focused on the interfacial molecular configurations in efficient OSC charge extraction by theoretical investigations and experiments, including small molecule-based bilayer-heterojunction (sm-BLHJ) and polymer-based bulk-heterojunction (p-BHJ) OSCs. We first examined a well-defined sm-BLHJ model system of OSC composed of p-type pentacene, an n-type perylene derivative, and a nanogroove-structured poly(3,4-ethylenedioxythiophene) (NS-PEDOT) hole extraction layer. The OSC with NS-PEDOT shows a 230% increment in the short circuit current density compared with that of the conventional planar PEDOT layer. Our theoretical calculations indicated that small variations in the microscopic intermolecular interaction among these interfacial configurations could induce significant differences in charge extraction efficiency. Experimentally, different interfacial configurations were generated between the photo-active layer and the nanostructured charge extraction layer with periodic nanogroove structures. In addition to pentacene, poly(3-hexylthiophene), the most commonly used electron-donor material system in p-BHJ OSCs was also explored in terms of its possible use as a photo-active layer. Local conductive atomic force microscopy was used to measure the nanoscale charge extraction efficiency at different locations within the nanogroove, thus highlighting the importance of interfacial molecular configurations in efficient charge extraction. This study enriches understanding regarding the optimization of the photovoltaic properties of several types of OSCs by conducting appropriate interfacial engineering based on organic/polymer molecular orientations. The ultimate power conversion efficiency beyond at least 15% is highly expected when the best state-of-the-art p-BHJ OSCs are combined with present arguments.

Charge transfer highways in polymer solar cells embedded with imprinted PEDOT:PSS gratings

Carrier transport highways induced by nanoimprinted PEDOT:PSS gratings play important roles in the enhancement of the electrical performances of P3HT:ICBA-based organic photovoltaic cells.

Analysis of a spatially dispersive displacement sensor utilizing an AlGaInP chip

We present a demonstration and analysis of an industrialized design of a spatially dispersive displacement sensor, which is composed of an AlGaInP gain chip in visible range, optical assembly, and a spectrum analyzer. The sensor utilizes the spatial dispersion of focus from the optical assembly and wavelength spectrum's deviation induced by the displacement of the target. As a result, the sensor delivers a quick and simple way of measuring displacement. By adapting the magnification and resolution of the optical assembly, a displacement sensor with a middle measurement range, ~10 microm, was obtained. However, we should note that 25 nm resolution is limited by the bandwidth and temperature fluctuation of the gain chip.

Spatially dispersive displacement sensor utilizing a semiconductor gain chip

We demonstrate the development of a simply equipped displacement sensor utilizing spatially dispersive confocal technology. It feeds the amplified spontaneous emission (ASE) of a laser diode to a wavelength-selective feedback structure that corresponds to the position of a measured surface. The displacement sensor has a detecting range of 4 microm and precision of less than 2 nm, as proven by the analysis of the spectral shifts of the multipassed amplified output ASE. As compared with traditional sensors, the displacement sensor presented in our study requires fewer components and has as high precision as complex systems and a higher measurement rate due to the simpler strategy of displacement determination.

Induction of connexin 37 expression in a rat model of neuropathic pain

Activation of cutaneous C-fibers by capsaicin or sciatic nerve transection increases the number of astrocytic gap junctions as well as the levels of connexin 43 in the dorsal horn on the stimulated side. Changes in connexin 37 mRNA expression following nerve injury have not been previously documented. We examined the role of gap junction protein connexin 37 in neuropathic hypersensitivity following peripheral nerve injury. Study results showed ipsilaterally increased connexin 37 mRNA levels proximally and distally in rat sciatic nerves after injury and behavioral thermal hyperalgesia at 7 and 14 days. Proximal and distal connexin 37 mRNA levels returned to baseline by 21 days. Sciatic nerve connexin 37 mRNA increases were proportional to the extent of thermal hyperalgesia, but skin, muscle, and lumbar spinal cord connexin 37 mRNA showed no significant changes. Neuropathic pain relief correlated with downregulation of connexin 37 mRNA. Results indicate that upregulation of connexin 37 mRNA following sciatic nerve injury correlates with subsequent thermal hyperalgesia, which suggests that gap junctions (connexin 37) are responsible for the hyperexcitability following peripheral nerve injury.

Peroxisome proliferator-activated receptors (PPAR) and the mitochondrial aldehyde dehydrogenase (ALDH2) promoter in vitro and in vivo

BACKGROUND

The aldehyde dehydrogenase 2 (ALDH2) promoter contains a nuclear receptor response element (NRRE) that represents an overlapping direct repeat-1 (DR-1) and -5 (DR-5) element. Because DR-1 elements are preferred binding sites for peroxisome proliferator-activated receptors (PPARs), we tested the hypothesis that PPARs regulate ALDH2 expression.

METHODS

We examined the ability of PPAR isoforms to bind to the ALDH2 NRRE in electrophoretic mobility shift assays, their ability to activate the transcription of promoter-reporter constructs containing this NRRE, the effect of PPAR ligands on ALDH2 expression in liver, and the role of the PPARalpha on the expression of ALDH2 by using PPARalpha-null mice.

RESULTS

In vitro translated PPARs bound the ALDH NRRE with high affinity. Mutation of the NRRE indicated that binding was mediated by the DR-1 element. Cotransfection of PPAR expression plasmids showed that PPARalpha had no effect on expression of heterologous promoter constructs containing the NRRE. PPARgamma slightly induced expression, whereas PPARdelta repressed basal activity of the promoter and blocked induction by hepatocyte nuclear factor 4. Treatment of rats with the PPAR ligand clofibrate repressed expression of ALDH2 in rats fed either stock rodent chow or a low-protein diet. Consistent with the transfection data, expression of ALDH2 protein was not different in PPARalpha-null mice. Treatment of the mice with the PPARalpha agonist WY14643 slightly decreased the level of ALDH2 protein in both wild-type and PPARalpha-null mice, suggesting that the effect of WY14643 was not mediated by the receptor.

CONCLUSIONS

These data indicate that ALDH2 is not part of the battery of lipid metabolizing enzymes and proteins regulated by PPARalpha

Creutzfeldt-Jakob disease: heat shock protein 70 mRNA levels in mononuclear blood cells and clinical study

Prion diseases such as Creutzfeldt-Jakob disease (CJD) are associated in most cases with the accumulation of an unusual isoform of prion protein (PrPSC). PrPSC is derived from the abnormal folding of the cellular isoform of prion protein (PrPC). On the other hand, heat shock protein is known to ensure proper protein assembly and folding and to facilitate proteolytic digestion of abnormal or denatured proteins. Many studies have therefore hypothesized that heat shock protein is linked to prion disease. We examined the relationship between heat shock protein HSP70 and prion disease in CJD patients. HSP70 mRNA levels in mononuclear blood cells (MBCs) were compared in 14 CJD patients (10 confirmed by histo-pathological study), 12 vascular dementia (VD) patients, 16 patients with Parkinson's disease and dementia (PD) and 14 nondemented control subjects. The possible correlation between HSP70 mRNA expression levels and clinical findings was also evaluated. HSP70 mRNA expression levels in MBCs were measured by northern blotting. HSP70 mRNA levels in MBCs from patients with CJD were significantly higher than those from patients with VD or PD and in nondemented controls. Age at symptom onset, dementia severity, disease duration and neuroimaging grade of CJD patients were not correlated with relative HSP70 mRNA levels. No significant relationship between HSP70 mRNA levels and ageing was found. These results suggest that measurement of HSP70 mRNA in MBCs might provide an auxiliary tool for the diagnosis of CJD.

Experimental focal segmental glomerulosclerosis in mice

Although a lot of animal models of proteinuria have been established, proposals for the mechanisms of proteinuria are still controversial. In this work, during an 18-day trial, mice injected with a single dose of adriamycin (AD) rapidly showed combined glomerular albuminuria and immunoglobulinuria, progressively elevated levels of nitrite/nitrate in urine, hypercholesterolemia, abnormal renal function, segmentally or globally glomerular hyalinosis/sclerosis associated with tubular atrophy, enhanced glomerular deposition of immunoglobulins and fibrinogen, augmented expression of matrix components in the whole glomerular tuft, and loss of glomerular negative charge property. These laboratory and pathological features are comparatively similar to those of human focal segmental glomerulosclerosis in the advanced state. Juxtamedullary glomeruli appear to be more susceptible to the AD-related nephrotoxicity than those in the superficial renal cortex. A change in size-dependent glomerular permselectivity may precede a charge-dependent defect in glomeruli in this mouse model of proteinuria. Data in this study confirm the hypothesis of glomerular hyperfiltration involved in the pathogenesis of this chronic glomerulopathy associated with proteinuria in mice. In addition, nitric oxide may play a crucial role in the progression of the chronic glomerulopathy model.

Involvement of immunopathogenic mechanisms in a spontaneously occurring glomerulopathy in mice

Mice have been found to be susceptible to spontaneous renal localization of immune deposits. However, the significance of these immune deposits is still debated. We investigated the immunopathogenesis of a naturally occurring glomerulopathy associated with progressive proteinuria and glomerulosclerosis in 75 BALB/c mice. The mice were divided into five groups of 15 and killed at the age of 1, 3, 6, 12, or 18 months for laboratory and renal pathologic studies. These mice showed persistently increasing serum levels of immune complexes, a marked increase of glomerular immune deposits which were capable of fixing C3, and interstitial infiltration of lymphocytes and plasma cells, followed by the occurrence of proteinuria, mesangiopathy, and glomerulosclerosis. Our findings suggest that an immune system mediated process occurred in the kidneys of the mice tested.

Protein oxidation and turnover

All biomacromolecules are faced with oxidative stress. Oxidation of a protein molecule always induces inactivation of the molecule and introduces a tag to that molecule. These modified protein molecules are prone to degradation in vivo by the proteasome system. Coupling of protein modification and degradation of chemically modified proteins is one of the normal protein turnover pathways in vivo. We call this a 'chemical apoptosis' process, which is one of the early manifestations of programmed cell death. Impairment of the proteasome system leads to accumulation of modified nonfunctional proteins or 'aged proteins' that might cause various clinical syndromes including cataractogenesis, premature aging, neurological degeneration and rheumatoid disease. The metal-catalyzed oxidation of biomacromolecules provides an excellent artificial aging system in vitro. The system is very useful in the characterization of structure and function relationships of proteins (enzymes), especially in those containing metal binding domain(s), because the oxidation is always followed by an affinity cleavage at the metal binding site(s) that allows easy identification and further characterization.

The retinoid X receptor response element in the human aldehyde dehydrogenase 2 promoter is antagonized by the chicken ovalbumin upstream promoter family of orphan receptors

Two tandem sites in the aldehyde dehydrogenase 2 promoter (designated FP330-5' and FP330-3') that bind members of the nuclear receptor superfamily were recently identified. Antibodies against apolipoprotein regulatory protein (ARP-1) altered DNA-protein interactions in electrophoretic mobility shift assays using oligonucleotides representing either promoter site and rat liver or cultured cell nuclear extracts. In vitro-translated chicken ovalbumin upstream promoter transcription factor (COUP-TFI), ARP-1, or ErbA-related protein 2 (Ear2) bound both sites. In addition, ARP-1/RXR, COUP-TFI/RXR, and ARP-1/COUP-TFI heterodimers bound the FP330-3' site. Mutagenesis of the FP330-3' site indicated that a DR-1 element was the preferred binding site for these factors. Transfected expression plasmids for these factors suppressed basal expression of reporter constructs containing the FP330-3' sites and the induction of the reporter by RXRalpha plus retinoic acid. Mutation of the two sites increased activity of a construct driven by 600 bp of the ALDH2 promoter in cell lines expressing COUP-TFs. The ALDH2 FP330-3' site appears to represent a complex nuclear receptor response element that is activated by RXRs and HNF-4 but repressed by members of the COUP-TF family.

Lysine residues 162 and 340 are involved in the catalysis and coenzyme binding of NADP(+)-dependent malic enzyme from pigeon

Alanine-scanning site-directed mutagenesis was carried out on all conserved lysine residues of pigeon cytosolic NADP(+)-dependent malic enzyme. Only two mutant enzymes, K162A and K340A, showed significant effect on their kinetic parameters. Both mutant enzymes have K(m) values for Mn(2+) and l-malate similar to those of wild-type. The K(m) value for NADP(+) of K162A is identical to that of wild-type. However, K162A demonstrated a 235-fold decrease in the k(cat) value (0.17 +/- 0.01 vs 40.0 +/- 1.3 s(-1)). These data suggested that the side chain of K162 is important for the enzyme catalytic reaction. We propose that the epsilon-amino group of K162 may serve as a general acid to protonate the 3-carbon of enolpyruvate after decarboxylation. The K340A mutant demonstrated no effect on the k(cat) value. However, its K(m) value for NADP(+) was increased by a factor of 65 (225.7 +/- 5.07 vs 3.49 +/- 0.05 microM). We propose that the NADP(+) specificity is determined by the electrostatic interaction between the epsilon-amino group of K340 and 2'-phosphate of NADP(+).

Heat shock modulates prion protein expression in human NT-2 cells

The pathological hallmarks of Prion disease are cortical spongiform changes and neuronal loss, which are induced by the accumulation of the scrapie-isoform prion protein (PrP(Sc)). PrP(Sc) is derived from a post-translational modification of the cellular form of prion protein (PrP(C)). Heat-shock proteins, a group of molecular chaperones, are involved in the degradation of denatured proteins and post-translational folding of newly synthesized polypeptides. In an attempt to examine any possible relationship between heat shock stress and an induction of prion protein (PrP), human NT-2 cells were treated with heat shock at 42 degrees C for 30 min. After heat-shock treatment, both the level of mRNA and PrP(C) protein were analyzed at various time points by Northern and Western blot, respectively. There was a 1.5- to 2.5-fold increase in PrP mRNA levels 1 and 3h following heat shock. In addition, a two-fold increase in protein level of PrP was found 3 h after heat-shock treatment. These results suggest that cellular stress induces the elevation of both PrP mRNA and protein synthesis. The up-regulation of prion-protein mRNA and protein, implies that PrP may play a role in cellular stress.

Characterization of the functional role of Asp141, Asp194, and Asp464 residues in the Mn2+-L-malate binding of pigeon liver malic enzyme

Pigeon liver malic enzyme was inactivated and cleaved at Asp141, Asp194, and Asp464 by the Cu2+-ascorbate system in acidic environment. Site-specific mutagenesis was performed at these putative metal-binding sites. Three point mutants, D141N, D194N, and D464N; three double mutants, D(141,194)N, D(194,464)N, and D(141,464)N; and a triple mutant, D(141,194,464)N; as well as the wild-type malic enzyme (WT) were successfully cloned and expressed in Escherichia coli cells. All recombinant enzymes, except the triple mutant, were purified to apparent homogeneity by successive Q-Sepharose and adenosine-2',5'-bisphosphate-agarose columns. The mutants showed similar apparent Km,NADP values to that of the WT. The Km,Mal value was increased in the D141N and D194N mutants. The Km,Mn value, on the other hand, was increased only in the D141N mutant by 14-fold, corresponding to approximately 1.6 kcal/mol for the Asp141-Mn2+ binding energy. Substrate inhibition by L-malate was only observed in WT, D464N, and D(141,464)N. Initial velocity experiments were performed to derive the various kinetic parameters. The possible interactions between Asp141, Asp194, and Asp464 were analyzed by the double-mutation cycles and triple-mutation box. There are synergistic weakening interactions between Asp141 and Asp194 in the metal binding that impel the D(141,194)N double mutant to an overall specificity constant [k(cat)/(Kd,Mn Km,Mal Km,NADP)] at least four orders of magnitude smaller than the WT value. This difference corresponds to an increase of 6.38 kcal/mol energy barrier for the catalytic efficiency. Mutation at Asp464, on the other hand, has partial additivity on the mutations at Asp141 and Asp194. The overall specificity constants for the double mutants D(194,464)N and D(141,464)N or the triple mutant D(141,194,464)N were decreased by only 10- to 100-fold compared to the WT. These results strongly suggest the involvement of Asp141 in the Mn2+-L-malate binding for the pigeon liver malic enzyme. The Asp194 and Asp464, which may be oxidized by nonspecific binding of Cu2+, are involved in the Mn2+-L-malate binding or catalysis indirectly by modulating the binding affinity of Asp141 with the Mn2+.

Crystallization and preliminary x-ray diffraction analysis of malic enzyme from pigeon liver

Recombinant pigeon-liver malic enzyme was expressed in Escherichia coli and purified to homogeneity. Two different crystal forms were grown by the hanging-drop vapour-diffusion method. Both types of crystals belong to the tetragonal space group P4(2)22, with unit-cell dimensions a = b = 163.8, c = 174.3 A for the octahedral crystals and a = b = 124.5, c = 179.2 A for the rod-like crystals. X-ray diffraction data were collected at 100 K using a synchrotron-radiation X-ray source. The Matthews parameter suggests that there are four and two molecules per asymmetric unit for the larger and the smaller tetragonal unit cells, respectively.

An A/G polymorphism in the promoter of mitochondrial aldehyde dehydrogenase (ALDH2): effects of the sequence variant on transcription factor binding and promoter strength

INTRODUCTION

The strong protective effect of the ALDH2*2 mutation on risk of alcoholism suggests that other mutations that reduce mitochondrial aldehyde dehydrogenase (ALDH) activity in the liver might also deter drinking. This study describes a polymorphic locus found in the promoter of the ALDH2 gene that affects expression of reporter constructs.

METHODS

Polymerase chain reaction (PCR)-based sequencing was used to search for polymorphisms. The ability of the promoter variants to bind transcription factors apolipoprotein A regulatory protein 1 (ARP-1) and chicken ovalbumin upstream promoter-transcription factor (COUP-TF) was tested in gel retardation assays using in vitro synthesized transcription factors. The variant promoters were tested for transcriptional activity using a heterologous promoter system and transient transfection assays.

RESULTS

A common polymorphism (A or G) in the human ALDH2 promoter region was found at -361 base pair (bp) from the translation start site. This polymorphism was found at different frequencies in African Americans, Caucasians, and Asians. The polymorphism occurs adjacent to the core binding motif for the transcription factors COUP-TF and ARP-1. Competition and binding affinity determinations did not show differences in the ability of these two sequences to bind the factors. Reporter genes containing these elements upstream of a basal thymidine kinase promoter had similar activity when transfected into a fibroblast (CV-1) cell line. However, the reporter containing the G allele was more active than that containing the A allele in hepatoma (H4IIEC3) cells.

CONCLUSIONS

The -361 bp A/G polymorphism is common in all racial groups tested. The G allele was more active than the A allele in a transfection assay. The basis for this difference is not known. If the differences in activity of the promoter constructs were paralleled by differences in ALDH2 enzyme activity in the liver, this polymorphism could affect risk of alcoholism.

Conformational stability of the N-terminal amino acid residues of mutated recombinant pigeon liver malic enzymes

Pigeon liver malic enzyme has an N-terminal amino acid sequence of Met-Lys-Lys-Gly-Tyr-Glu-Val-Leu-Arg-. Our previous results indicated that the N-terminus of the enzyme is located at or near the enzyme's active center involved in Mn(II)-L-malate binding and is also near to the subunits' interface. In the present study, the conformational stability of the various deletion (delta) and substitution mutants at Lys2/Lys3 of the enzyme was investigated with chemical and thermal sensitivities. The lysine residue at position 2 or 3 seems to be crucial for the correct active site conformation, probably through an ion-pairing with Glu6. Deletion at Lys2 or Lys3, delta(K2/K3), and the double mutant K(2,3)E were much less stable than the wild-type enzyme towards chemical denaturation. Kinetic analysis of the thermal inactivation at 58 degrees C of the recombinant enzymes indicated that mutation at position 3 to alanine (K3A) endows the protein with extra stability compared with the wild-type enzyme. K3A is also stable towards chemical denaturation. The concentration of urea that causes half unfolding, [urea]0.5, for K3A is 3.25 M compared with 2.54 M for the wild-type enzyme. The K3A mutant of malic enzyme might therefore have potential practical applications.

Parathyroid hormone regulates the rat collagenase-3 promoter in osteoblastic cells through the cooperative interaction of the activator protein-1 site and the runt domain binding sequence

Parathyroid hormone induces collagenase-3 gene transcription in rat osteoblastic cells. Here, we characterized the basal, parathyroid hormone regulatory regions of the rat collagenase-3 gene and the proteins involved in this regulation. The minimal parathyroid hormone-responsive region was observed to be between base pairs -38 and -148. Deleted and mutated constructs showed that the activator protein-1 and the runt domain binding sites are both required for basal expression and parathyroid hormone activation of this gene. The runt domain site is identical to an osteoblast-specific element-2 or acute myelogenous leukemia binding sequence in the mouse and rat osteocalcin genes, respectively. Overexpression of an acute myelogenous leukemia-1 repressor protein inhibited parathyroid hormone activation of the promoter, indicating a requirement of acute myelogenous leukemia-related factor(s) for this activity. Overexpression of c-Fos, c-Jun, osteoblast-specific factor-2, and core binding factor-beta increased the response to parathyroid hormone of the wild type (-148) promoter but not with mutation of either or both the activator protein-1 and runt domain binding sites. In summary, we conclude that there is a cooperative interaction of acute myelogenous leukemia/polyomavirus enhancer-binding protein-2-related factor(s) binding to the runt domain binding site with members of the activator protein-1 transcription factor family binding to the activator protein-1 site in the rat collagenase-3 gene in response to parathyroid hormone in osteoblastic cells.

Engineering of a stable mutant malic enzyme by introducing an extra ion-pair to the protein

A double mutant (R9E/M17K) of pigeon liver malic enzyme with glutamate and lysine replaced for arginine and methionine at positions 9 and 17, respectively, was found to be much more stable in urea and thermal denaturation, but was enzymatically less active than the wild-type enzyme (WT). Unfolding of the enzyme by urea produced a large red shifting of the protein fluorescence maximum from 320 to 360 nm, which was completely reversible upon dilution. Analysis of the denaturation curves monitored by enzyme activity lost suggested that a putative intermediate was involved in the denaturation process. The half unfolding urea concentration, measured by fluorescence spectral changes, increased from 2.24 M for WT to 3.13 M for R9E/M17K. The melting temperature increased by approximately 10 degrees C for R9E/M17K compared with that for WT. Kinetic analysis of the thermal inactivation at 58 degrees C also conformed to a three-state model with the rate constant for the intermediate state of R9E/M17K (k2 = 0.03 min(-1)) being much smaller than the WT value (k2 = 2.39 min(-1)). Results obtained from single mutants indicated that the decreasing enzyme activity of R9E/M17K was exclusively due to R9 mutation, which increased the K(mMn) and K(mMal) by at least one order of magnitude compared with WT. Consequently, a decrease occurred in the specificity constant [k(cat)/(K(mMm)K(mNADP)K(mMal))] for the R9 mutants at least four orders of magnitude smaller than the WT. M17K has similar properties to the WT, while R9E is more labile than the WT enzyme. The above results indicate that the extra stability gained by the double mutant possibly occurs through the introduction of an extra ion-pair between E9 and K17, which freezes the double mutant in the putative intermediate state. Examination of the N-terminal amino acid sequence of pigeon liver malic enzyme reveals that position 15 is also a lysine residue. Since the R9E mutant, which has an extra Glu9-Lys15 ion-pair, is less stable than the WT, we conclude that the contribution to malic enzyme stability is specific for the Glu9-Lys17 ion-pair.

Administration of dexamethasone induces proteinuria of glomerular origin in mice

The administration of glucocorticoids has been reported to exacerbate proteinuria in a few patients with glomerulonephritis. This effect has not been well recognized, and the pathogenetic mechanism responsible for this phenomenon remains to be clarified. In this study, we observed that a high daily oral dose (0.5 mg/kg body weight) of dexamethasone was capable of inducing overt proteinuria in mice, beginning on day 5 and persisting for a 19-day duration. One fourth of mice also intermittently presented with slight hematuria beginning on day 12. Renal lesions in the dexamethasone-treated mice, which were killed on day 23, were characterized by mild mesangial expansion, segmental or global hyalinosis/sclerosis in deep cortical glomeruli, and focal tubular changes. No glomerular inflammatory cell infiltration or proliferative lesion was noted in any of the mice. Ultrastructural features of glomeruli included mesangial widening characterized by either an increase of mesangial matrix, dilated mesangial channels filled with slightly electron-dense material or mesangial lysis-like appearance showing intracytoplasmic microcysts filled with electron-lucent material, and evidence to support injury of endothelial cells, erythrocytes, and podocytes. An immunofluorescence study revealed enhanced glomerular deposition of IgG, IgA, IgM, and fibrinogen (P < 0.001, compared with normal control mice), but no glomerular C3 deposition was identified in any of the dexamethasone-treated mice. Charge analysis showed no impairment in anionic property of glomerular tufts in the dexamethasone-treated mice. In addition, the dexamethasone-induced proteinuria was greatly attenuated by treatment with a low molecular weight heparin, although it was not reduced by an angiotensin-converting enzyme inhibitor. Data from these experiments suggest that a large dose of glucocorticoids is potentially nephrotoxic. Alteration of a size-dependent permeability may predominantly contribute to the dexamethasone-induced proteinuria. However, the effect of glomerular hyperfiltration may be only partially involved in the pathogenesis of this dexamethasone-induced glomerulopathy in mice.

Interleukin-1 receptor antagonist modulates the progression of a spontaneously occurring IgA nephropathy in mice

Cytokines, such as interleukin-1 (IL-1), may play a key role in the pathogenesis of IgA nephropathy (IgAN). This study was conducted to evaluate the effects of IL-1 receptor antagonist (IL-1ra) in the treatment of a spontaneously occurring experimental IgAN in established phase. ddY mice (12/group) were injected twice daily with 3 mg/kg of IL-1ra, intraperitoneally, for 8 consecutive weeks. The placebo mice were injected with saline only. As normal controls, ddY mice, which were not treated with IL-1ra or saline, were killed at 6 weeks of age. Results showed a significant reduction of proteinuria in the IL-1ra-treated mice, compared with saline-treated mice (urinary albumin/creatinine, 0.24 +/- 0.04 v 0.39 +/- 0.03, P < 0.001). A significant improvement of renal 51Cr-EDTA (ethylenediaminetetra-acetic acid) clearance was observed in the IL-1ra-treated mice (t1/2, 12 +/- 2.7 minutes, compared with saline-treated mice 25 +/- 2.0 minutes, P < 0.001). Similarly, serum levels of creatinine (1.0 +/- 0.4 v 2.4 +/- 0.3 mg/dL, P < 0.001) and urea nitrogen (46 +/- 6 v 58 +/- 2 mg/dL, P < 0.01) were significantly lower in IL-1ra-treated mice than in saline-treated mice. In renal tissue studies, the IL-1ra-treated mice exhibited significantly decreased mesangial cell proliferation, compared with saline-treated mice (P < 0.001), as shown by light and electron microscopy. In addition, the IL-1ra-treated mice showed significantly lower glomerular expression of collagen type IV, fibronectin, laminin, and IL-6 (P < 0.001) than saline-treated mice, although they still showed higher glomerular expression of collagen type IV (P < 0.01), fibronectin (P < 0.01), laminin (P < 0.001), IL-1 (P < 0.001), and IL-6 (P < 0.01) than did normal control mice. Meanwhile, glomerular C3 deposition was significantly lower in IL-1ra-treated mice than in saline-treated mice (P < 0.001). These findings indicate that IL-1ra partially prevented the progression of spontaneously occurring IgAN in this experimental model. Data from these experiments also confirm the pathogenic effects of IL-1 in the established phase of IgAN in ddY mice.

Functional roles of the N-terminal amino acid residues in the Mn(II)-L-malate binding and subunit interactions of pigeon liver malic enzyme

Pigeon liver malic enzyme has an N-terminal amino acid sequence of Met-Lys-Lys-Gly-Tyr-Glu-. In this work, various mutants of the enzyme with individual or combinational deletion (delta) or substitution at these amino acids were constructed and functionally expressed in Escherichia coli cells. A major protein band corresponding to an Mr of approximately 65000 was observed for all recombinant enzymes in sodium dodecyl sulfate polyacrylamide gel electrophoresis. However, when examining by polyacrylamide gel electrophoresis under native conditions, the recombinant enzymes were found to possess a tetrameric structure with Mr approximately 260000 or a mixture of tetramers and dimers with the exception of delta(K2K3G4) and delta(1-16) mutants, which existed exclusively as dimers at the protein concentration we employed. K3A and K3E also dissociated substantially. K(2,3)A was a tetramer but K(2,3)E essentially existed as dimers. All tetramers and dimers were enzymatically active in the gels. All mutants displayed a similar apparent Km value for NADP+. The apparent Km for L-malate and Mn(II), on the other hand, was increased by 4-27-fold for the delta(K2/K3) and the delta(1-16) mutants. The small binding affinity of delta(K2/K3) with Mn(II)-L-malate was specific. With additional deletion at positions 3 and/or 4, the delta(K2K3), delta(K2G4/K3G4) or delta(K2K3G4) mutants exhibited similar kinetic properties for the wild type. The lysine residues at the positions 2 or 3 seem to be crucial for the correct active site conformation. The results indicate that the N-terminus of malic enzyme is located at the Mn(II)-L-malate binding domain of the active center and is also near the subunit's interface. These results were interpreted with our asymmetric double-dimer model for the enzyme in which the N-terminus was involved in the head-to-tail monomer-monomer interactions but not the dimer-dimer interactions.

Parathyroid hormone induces c-fos promoter activity in osteoblastic cells through phosphorylated cAMP response element (CRE)-binding protein binding to the major CRE

Many parathyroid hormone (PTH)-mediated events in osteoblasts are thought to require immediate early gene expression. PTH induces the immediate early gene, c-fos, in this cell type through a cAMP-dependent pathway. The present work investigated the nuclear mechanisms involved in PTH regulation of c-fos in the osteoblastic cell line, UMR 106-01. By transiently transfecting c-fos promoter 5' deletion constructs into UMR cells, we demonstrated that PTH induction of the c-fos promoter requires the major cAMP response element (CRE). Point mutations created in the major CRE within the largest construct inhibited both PTH-stimulated and basal expression. This element, therefore, performs concerted basal and PTH-responsive cis-acting functions. Gel retardation and Western blotting techniques revealed that CRE-binding protein (CREB) constitutively binds the major CRE but becomes phosphorylated at its cAMP-dependent protein kinase consensus recognition site following PTH treatment. CREB was functionally implicated in c-fos regulation by coexpressing a dominant CREB repressor, KCREB (killer CREB), with the c-fos promoter constructs. KCREB suppressed both basal and PTH-mediated c-fos induction. We conclude that PTH activates c-fos in osteoblasts through cAMP-dependent protein kinase-phosphorylated CREB interaction with the major CRE in the promoter region of the c-fos gene.

Involvement of Phe19 in the Mn(2+)-L-malate binding and the subunit interactions of pigeon liver malic enzyme

A triple mutant, F19S/N250S/L353Q, of pigeon liver malic enzyme was found to have no detectable enzymatic activity [Chou, W.-Y., Huang, S.-M., & Chang, G.-G. (1994) Arch. Biochem. Biophys. 310, 158-166]. In the present study, point mutants at these positions (F19S, N250S, and L353Q) were prepared by site-directed mutagenesis. Both N250S and L353Q have kinetic properties similar to those of the wild-type. On the other hand, the K(m)(app) values for both Mn2+ and L-malate of F19S were increased by approximately 10-fold, while the kcat value was decreased by 5-fold, which results in a decrease of the apparent catalytic efficiency (kcat/K(mNADP)K(mMal)K(mMn) by approximately 300-fold. These results clearly indicate that the F19S mutation is mainly responsible for the undetectable enzyme activity of the triple mutant. Three more Phe19 mutants (F19Y, F19G, and F19A) were then prepared. There is a direct correlation between the size of the substitutes and the affinities for Mn2+ and L-malate. The kinetic parameters for F19Y were similar to those for wild-type. Both F19A and F19G reveal a 5-fold decrease of kcat values. Two K(dMn) values for the high- and low-affinity sites, respectively, were detectable for the wild-type. On the contrary, only one K(dMn) value was detected for the F19 mutants, which was increased in the order of F19G > F19A > F19S > F19Y, with F19G being the most affected mutant. The K(mMal) values of F19G and F19A were increased 100- and 6-fold, respectively. The catalytic efficiency (kcat/K(mNADP)K(dMal)K(dMn)) of F19G was decreased to only 0.01% of that of the wild-type. The above results clearly indicate that the hydrophobic aromatic ring at position 19 plays a critical role in L-malate and Mn2+ binding. Furthermore, all mutants that have a small residue at position 19 exist as monomers. Therefore, Phe19 may locate in or near the regions for Mn(2+)-L-malate binding as well as for the subunit contact. These results are compatible with the asymmetric model for the quaternary structure of malic enzyme we proposed previously [Chang, G.-G., Huang, T.-M., Huang, S.-M., & Chou, W.-Y. (1994) Eur. J. Biochem. 225, 1021-1027]. The possible roles of the N-terminus of malic enzyme were also addressed.

The production and characterization of a modified recombinant interleukin-1 receptor antagonist

The increasingly complex cytokine network involves both positive and negative regulatory pathways. Natural inhibitors of cytokines are of great importance both as analytical tools and as potential therapeutic agents. Interleukin-1 (IL-1) inhibitory bioactivity including a specific receptor antagonist of IL-I (IL-1ra) has been described both in cultured cell supernatants and in human body fluids. In the current studies, the cDNA of IL-1ra from human monocytes was obtained by the techniques of mRNA isolation and reverse transcription/polymerase chain reaction (RT/PCR). The IL-1ra cDNA/pET-15b was transfected into DE3 cells and the recombinant protein expressed. The purified protein was demonstrated as a single band with molecular mass of 20 KD by SDS-PAGE; it had strong IL-1 inhibitory activity. This IL-1 inhibitor competed with IL-1 for their receptor as assessed by flow cytometer. The existence of this naturally occurring specific cytokine receptor antagonist may lead to a different perspective of the cytokine network. The availability of this recombinant IL-1 receptor antagonist allows us to test its role on the cytokine network, and on possible disease modification.

Nonidentity of the cDNA sequence of human breast cancer cell malic enzyme to that from the normal human cell

A cDNA coding for human breast cancer cell cytosolic NADP(+)-dependent malic enzyme was obtained. This cDNA is composed of a length of 2084 base pairs, with 1698 base pairs coding for 565 amino acid residues and a length of 386 base pairs representing a 3'-noncoding region. Comparing this nucleotide sequence with that from the normal human tissue [Loeber, G., Dworkin, M. B., Infante, A., and Ahorn, H. (1994), FEBS Lett. 344, 181-186] reveals that three nucleotides in the open reading frame and the length of 3'-noncoding region of the cDNA are different. One of the changes results in a substitution of serine at position 438 for proline, which, however, may not cause significant changes in the predicted secondary structure. A partial cDNA lacking the first 84 nucleotides in the open reading frame was successfully cloned and expressed functionally in Escherichia coli cells. Its Km value for L-malate (1.21 +/- 0.11 mM) is four times higher than that for the natural human breast cancer cell malic enzyme (0.29 +/- 0.04 mM) but similar to that for the full-length recombinant enzyme (1.06 +/- 0.07 mM). The Km values for Mn2+ and NADP+ (0.26 +/- 0.03 and 0.97 +/- 0.4 microM, respectively) are similar to those for the natural enzyme (0.12 +/- 0.02 and 1.9 +/- 0.3 microM, respectively) or the recombinant wild-type enzyme (0.56 +/- 0.04 and 0.44 +/- 0.02 microM, respectively). A recombinant pigeon liver malic enzyme without the first 13 amino acid residues was used for comparison. The Km values for L-malate and Mn2+ of the truncated enzyme (11.2 +/- 0.9 mM and 61.2 +/- 4.6 microM, respectively) are over 40 times larger than those for the natural pigeon liver malic enzyme (0.21 +/- 0.02 mM and 1.06 +/- 0.08 microM, respectively) or the recombinant wild-type enzyme (0.25 +/- 0.01 mM and 1.48 +/- 0.05 microM, respectively). We suggest that the N-terminus of malic enzyme may be required for the substrate binding during the catalytic cycle.

Complete resolution of diastolic mitral regurgitation in chronic, but not acute aortic regurgitation after aortic valve replacement--a transesophageal echocardiography study

A 65-year-old male was admitted with progressive dyspnea on exertion. Severe aortic regurgitation (AR) had been disclosed by transthoracic echocardiography 10 mon previously. Aortic valve replacement was proposed and intraoperative transesophageal echocardiography on color Doppler imaging revealed severe aortic regurgitation, moderate global hypokinesis of the left ventricle and mild-to-moderate diastolic mitral regurgitation. The regurgitant jet was seen to pass through the posterior mitral leaflet in a direction toward the center of left atrium. Mitral valve perforation was suspected. But mitral valve was found to be intact after a thorough exploration. Surgery proceeded uneventfully and diastolic mitral regurgitation was resolved completely after the aortic valve was successfully replaced. Diastolic mitral regurgitation has been reported to be closely related to acute AR, but the picture differs somewhat from the present example. The possible cause for this disease presentation is to be further investigated.

The regulation and regulatory role of collagenase in bone

Interstitial collagenase plays an important role in both the normal and pathological remodeling of collagenous extracellular matrices, including skeletal tissues. The enzyme is a member of the family of matrix metalloproteinases. Only one rodent interstitial collagenase has been found but there are two human enzymes, human collagenase-1 and -3, the latter being the homologue of the rat enzyme. In developing rat and mouse bone, collagenase is expressed by hypertrophic chondrocytes, osteoblasts, and osteocytes, a situation that is replicated in a fracture callus. Cultured osteoblasts derived from neonatal rat calvariae show greater amounts of collagenase transcripts late in differentiation. These levels can be regulated by parathyroid hormone (PTH), retinoic acid, and insulin-like growth factors, as well as the degree of matrix mineralization. Much of the work on collagenase in bone has been derived from studies on the rat osteosarcoma cell line, UMR 106-01. All bone-resorbing agents stimulate these cells to produce collagenase mRNA and protein, with PTH being the most potent stimulator. Determination of secreted levels of collagenase has been difficult because UMR cells, normal rat osteoblasts, and rat fibroblasts possess a scavenger receptor that removes the enzyme from the extracellular space, internalizes and degrades it, thus imposing another level of control. PTH can also regulate the abundance of the receptor as well as the expression and synthesis of the enzyme. Regulation of the collagenase gene by PTH appears to involve the cAMP pathway as well as a primary response gene, possibly Fos, which then contributes to induction of the collagenase gene. The rat collagenase gene contains an activator protein-1 sequence that is necessary for basal expression, but other promoter regions may also participate in PTH regulation. Thus, there are many levels of regulation of collagenase in bone perhaps constraining what would otherwise be a rampant enzyme.

Selective oxidative modification and affinity cleavage of pigeon liver malic enzyme by the Cu(2+)-ascorbate system

Pigeon liver malic enzyme was rapidly inactivated by micromolar concentration of Fe2+ in the presence of ascorbate at neutral pH. The inactivated enzyme was subsequently cleaved by the Fe(2+)-ascorbate system at the chemical bond between Asp258 and Ile259 (Wei, C.H., Chou, W.Y., Huang, S.M., Lin, C.C., and Chang, G.G. (1994) Biochemistry, 33, 7931-7936), which was confirmed by site-specific mutagenesis (Wei, C.H., Chou, W.Y., and Chang, G.G. (1995) Biochemistry 34, 7949-7954). In the present study, at neutral pH, Cu2+ was found to be more reactive in the oxidative modification of malic enzyme and the enzyme was cleaved in a similar manner as Fe2+ did. At acidic pH, however, Fe2+ was found to be ineffective in oxidative modification of the enzyme. Nevertheless, Cu2+ still caused enzyme inactivation and cleaved the enzyme at Asp141-Gly142, Asp194-Pro195, or Asp464-Asp465. Mn2+ and L-malate synergistically protect the enzyme from Cu2+ inactivation at acidic pH. Cu2+ is also a competitive inhibitor versus Mn2+ in the malic enzyme-catalyzed reaction with Ki value 70.3 +/- 5.8 microM. The above results indicated that, in addition to the previously determined Asp258 at neutral pH, Asp141, Asp194, and Asp464 are also the coordination sites for the metal binding of malic enzyme. We suggest that the mechanism of affinity modification and cleavage of malic enzyme by the Cu(2+)-ascorbate system proceed in the following sequence. First, Cu2+ binds with the enzyme at the Mn2+ binding site and reduces to Cu+ by ascorbate. Next, the local oxygen molecules are reduced by Cu+, thereby generating superoxide or other reactive free radicals. These radicals interact with the susceptible essential amino acid residues at the metal-binding site, ultimately causing enzyme inactivation. Finally, the modified enzyme is cleaved into several peptide fragments, allowing the identification of metal site of the enzyme. The pH-dependent different specificities of metal-catalyzed oxidation system may be generally applicable for other enzymes or proteins.

Evidence for a Na+/Ca2+ exchanger in neuroblastoma x glioma hybrid NG108-15 cells

To determine whether NG108-15 cells contain a functional Na+/Ca2+ exchanger, we isotonically replaced extracellular Na+ with N-methyl-D-glucamine (NMG) and measured the effect on cytosolic Ca2+ concentration ([Ca2+]i) using the fluorescent Ca2+ indicator fura 2. Replacement with NMG alone had no effect on basal [Ca2+]i or the rise in [Ca2+]i evoked by 80 mM K+ or 10 microM bradykinin, but caused a larger [Ca2+]i increase when thapsigargin and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) were added to the cells; this enhanced [Ca2+]i increase could be reversed by adding Na+ back to the bathing buffer. The elevation in [Ca2+]i induced by thapsigargin and FCCP was inversely proportional to extracellular Na+ concentration. Furthermore, the exchanger operated in the reverse mode, as measured by either [Ca2+]i change or 45Ca2+ uptake. An 810 bp cDNA fragment of the exchanger was amplified by PCR; it differed by a single amino acid residue from the corresponding segment of the rat brain Na+/Ca2+ exchanger. These data suggest that a functioning Na+/Ca2+ exchanger exists in NG108-15 cells.

Identification of Asp258 as the metal coordinate of pigeon liver malic enzyme by site-specific mutagenesis

Pigeon liver malic enzyme was inactivated by ferrous sulfate in the presence of ascorbate. Manganese and some other divalent metal ions provided complete protection of the enzyme against the Fe(2+)-induced inactivation. The inactivated enzyme was subsequently cleaved by the Fe(2+)-ascorbate system at Asp258-Ile259, which was presumably the Mn(2+)-binding site of the enzyme [Wei, C. H., Chou, W. Y., Huang, S. M., Lin, C. C., & Chang, G. G. (1994) Biochemistry 33, 7793-7936]. For identification of Asp258 as the putative metal-binding site of the enzyme, we prepared four mutant enzymes substituted at Asp258 with glutamate (D258E), asparagine (D258N), lysine (D258K), or alanine (D258A), respectively. These mutant proteins were recombinantly expressed in a bacterial expression system (pET-15b) with a stretch of histidine residues attached at the N-terminus and were successfully purified to apparent homogeneity by a single Ni-chelated affinity column. Among the four mutants, only D258E possessed 0.8% residual activity after purification; all other purified mutants had < 0.0001% residual activity in catalyzing the oxidative decarboxylation of L-malate. The D258E mutant was susceptible to inactivation by the Fe(2+)-ascorbate system, albeit with much slower inactivation rate, and was protected by the Mn2+ to a lesser extent as compared to the wild-type enzyme. None of the mutants were cleaved by the Fe(2+)-ascorbate system under conditions that cleaved the natural or wild-type enzyme at Asp258.(ABSTRACT TRUNCATED AT 250 WORDS)