The factor V B-domain provides two functions to facilitate thrombin cleavage and release of the light chain

Blood coagulation factors V and VIII are homologous proteins that have the domain organization A1-A2-B-A3-C1-C2. Upon thrombin activation, the B-domains of both molecules are released. Previous studies on factor VIII showed that the B-domain was not required for thrombin cleavage or activity. In contrast, deletion of the factor V B-domain (residues 709 to 1545) yielded a molecule with sevenfold reduced procoagulant activity that was not cleaved by thrombin. However, this factor V B- domain deletion molecule was activated by factor Xa, although the fold- activation was 85% that of wild-type factor V. Thrombin cleavage of factor V occurs initially after residue 709 and subsequently after residues 1018 and 1545. The requirement for thrombin cleavage within the B-domain at residue 1018 was evaluated by mutagenesis of Arg1018 to Ile. In the resultant R1018I mutant, the rate of thrombin activation and appearance of maximal cofactor activity was delayed and was consistent with delayed cleavage of the light chain at residue 1545. In contrast, the rate of factor Xa activation in the R1018I mutant was not altered. This finding suggests that thrombin cleavage at 1018 facilitates subsequent thrombin cleavage at 1545. Further mutagenesis was used to study the requirement for sequences within the factor V B- domain for thrombin cleavage at residue 1545. Whereas the factor V deletion molecule removing residues 709 to 1545 was not cleaved by thrombin, a smaller B-domain deletion molecule (residues 709 to 1476) containing an acidic amino acid-rich region (residues 1490 to 1520) was effectively cleaved by thrombin. These results show that residues 1476 to 1545, which contain an acidic amino acid-rich region, were required for thrombin cleavage of the light chain. Introduction of an acidic amino acid-rich region from factor VIII (residues 337 to 372) into the factor V 709 to 1545 deletion also restored thrombin cleavage of the light chain. In contrast, similar replacement with the acidic region from the factor VIII light chain (residues 1649 to 1689) was significantly less effective in promoting thrombin cleavage of the light chain. This finding suggests that the different acidic regions in factors V and VIII are not functionally equivalent in their interaction with thrombin.(ABSTRACT TRUNCATED AT 400 WORDS)     

Quantum heat engine power can be increased by noise-induced coherence

Laser and photocell quantum heat engines (QHEs) are powered by thermal light and governed by the laws of quantum thermodynamics. To appreciate the deep connection between quantum mechanics and thermodynamics we need only recall that in 1901 Planck introduced the quantum of action to calculate the entropy of thermal light, and in 1905 Einstein’s studies of the entropy of thermal light led him to introduce the photon. Then in 1917, he discovered stimulated emission by using detailed balance arguments. Half a century later, Scovil and Schulz-DuBois applied detailed balance ideas to show that maser photons were produced with Carnot quantum efficiency (see Fig. 1A). Furthermore, Shockley and Quiesser invoked detailed balance to obtain the efficiency of a photocell illuminated by “hot” thermal light (see Fig. 2A). To understand this detailed balance limit, we note that in the QHE, the incident light excites electrons, which can then deliver useful work to a load. However, the efficiency is limited by radiative recombination in which the excited electrons are returned to the ground state. But it has been proven that radiatively induced quantum coherence can break detailed balance and yield lasing without inversion. Here we show that noise-induced coherence enables us to break detailed balance and get more power out of a laser or photocell QHE. Surprisingly, this coherence can be induced by the same noisy (thermal) emission and absorption processes that drive the QHE (see Fig. 3A). Furthermore, this noise-induced coherence can be robust against environmental decoherence.Open in a separate windowFig. 1.(A) Schematic of a laser pumped by hot photons at temperature T_h (energy source, blue) and by cold photons at temperature T_c (entropy sink, red). The laser emits photons (green) such that at threshold the laser photon energy and pump photon energy is related by Carnot efficiency (4). (B) Schematic of atoms inside the cavity. Lower level b is coupled to the excited states a and β. The laser power is governed by the average number of hot and cold thermal photons, and . (C) Same as B but lower b level is replaced by two states b₁ and b₂, which can double the power when there is coherence between the levels.Open in a separate windowFig. 2.(A) Schematic of a photocell consisting of quantum dots sandwiched between p and n doped semiconductors. Open circuit voltage and solar photon energy ℏν_h are related by the Carnot efficiency factor where T_c is the ambient and T_h is the solar temperature. (B) Schematic of a quantum dot solar cell in which state b is coupled to a via, e.g., solar radiation and coupled to the valence band reservoir state β via optical phonons. The electrons in conduction band reservoir state α pass to state β via an external circuit, which contains the load. (C) Same as B but lower level b is replaced by two states b₁ and b₂, and when coherently prepared can double the output power.Open in a separate windowFig. 3.(A) Photocell current j = Γρ_αα (laser photon flux P_l/ℏ_νl) (in arbitrary units) generated by the photovoltaic cell QHE (laser QHE) of Fig. 1C (Fig. 2C) as a function of maximum work (in electron volts) done by electron (laser photon) E_α - E_β + kT_c log(ρ_αα/ρ_ββ) with full (red line), partial (brown line), and no quantum interference (blue line). (B) Power of a photocell of Fig. 2C as a function of voltage for different decoherence rates , 100γ_1c. Upper curve indicates power acquired from the sun.Quantum mechanics began with the thermodynamic studies of Planck (1) and Einstein (2). In later work Einstein introduced the concept of stimulated emission via the detailed balance arguments (3). After the advent of the maser, Scovil and Schulz-DuBois (4) showed the quantum efficiency for the maser is described by a Carnot relation, and Shockley and Quiesser (5) used detailed balance limit to obtain a similar relation for a photocell. However, in the later part of the twentieth century it was shown that detailed balance could be superseded by using quantum coherence; this is manifested in lasing without inversion (6–8).Recent studies of a photocell QHE (9) show that it is possible to use microwave induced coherence to break detailed balance and enhance quantum efficiency (i.e., open circuit voltage). But what about enhancing the cell power? It takes energy to generate the microwaves—can we avoid this? A similar question can be asked concerning the laser QHE: Can we use quantum coherence to increase the net emitted laser power? More to the point, can we increase the power output of, for example, a photocell by using noise-induced coherence (10) such as that produced by Fano interference, to break detailed balance? The perhaps surprising (11) answer is yes.^*To answer this question, let us consider the case in which the lowest level is replaced by the pair of levels as in Fig. 1C. Now the plot thickens. In addition to producing a population inversion, the hot and cold photons can induce coherence between levels b₁ and b₂; where the amount of coherence is determined by the off diagonal matrix elements (12, 13) ρ_b1b2 = ρ₁₂ given in Eq. 3. We find that this coherence can markedly enhance the power [see also Fleischhauer et al. (14, 15) and Kozlov et al. (16)].The coherence induced by the hot and cold thermal radiation can be obtained from the density matrix equations of motion (see Appendix). To understand the physical origin of the noise-induced coherence we consider the probability ρ₁₁ of being in the state b₁, which obeys the following equation of motion with physical interpretation depicted on the next line: †, and are average number of hot and cold thermal photons (17) given by the Planck factors , .The power generated by the laser is [2]where is the average number of laser photons, g is atom-field coupling constant, and γ_l is the spontaneous decay rate at the lasing transition a → β.Thus, as discussed in Appendix and in SI Text, we solve the density matrix equations for populations ρ_aa and ρ_ββ as well as quantum coherence ρ₁₂ in steady state. For γ_1h = γ_2h = γ_h, γ_1c = γ_2c = γ_c the maximum coherence and laser power (18) are given by [3]where rate A is a function of decay rates γ_c and γ_h and the Planck average photon numbers , (see Appendix and SI Text). For the appropriate choice of parameters^‡, A = γ_h for the system with no coherence and A = 2γ_h with coherence—i.e., the power can be doubled (18), as in Fig. 1. Furthermore, Figs. 1 and ​and33 show that laser power can be significantly enhanced in the presence of coherence in general. Physically this is because the coherence can lead to faster removal of atoms from the ground state b_1,2 to the upper laser level a increasing useful work. That is, quantum coherence and interference enhances absorption of solar photons; because the terms result in redistribution of the population between b₁ and b₂ states such that the state with stronger coupling to the upper level a becomes more populated. This increases the number of absorbed photons and the current through the cell. Such interference can enhance photon absorption as in the present model or suppress it, which is the case for lasing without inversion.Next we consider the photocell QHE of Fig. 2 and study the influence of quantum interference and coherence on PV operation (i.e., power generated). Here we will consider a narrow band of frequencies as in the case of a multiplex array of photocells. That is, to optimally utilize a broad solar spectrum one can divide the incident solar flux into narrow frequency intervals, each of which is directed to a quantum dot photocell with its energy spacing matched to the incident light. Monochromatic solar radiation excites electrons from the valence to conduction states in the quantum dots. The “built-in” field in the depletion layer separates electrons and holes; however, they can radiatively recombine before being separated. In the complete analysis (see SI Text) we consider the general coupling associated with emission and absorption of solar photons and thermal phonons. This requires a little more elaborate density matrix treatment but the physics is essentially the same as the preceding laser problem. Furthermore, we here focus on the power generated, not the open circuit voltage, as is the case in ref. 9. However, the issue of breaking detailed balance in a photocell via quantum coherence remains the essence of the problem.In the photocell model (19, 20) of Fig. 2 B and C the cell current j and voltage V between levels α and β are given by (see Appendix) [4]where Γ is the decay of level α and ρ_ii(i = α,β) are the occupation probabilities of states in the conduction and lower energy valence reservoirs having energies E_α and E_β. If levels b₁ and b₂ are degenerate and γ_1h = γ_2h = γ_h the quantum coherence and power = jV are found to be [5]which is similar to Eq. 3 for the laser QHE in which the laser photon flux P_l/ℏν_l is now replaced by the photocell current. Factor B is similar to A and for the appropriate choice of parameters^§ B = γ_h/2 for the system with singlet shown in Fig. 2B, B = 2γ_h/3 for the doublet model (Fig. 2C), and no coherence and B = γ_h with full coherence—i.e., the photocell QHE power can be doubled by quantum coherence just as in the case of the laser.Fig. 3A shows the photocell current j (photon flux P_l/ℏν_l) as a function of voltage (energy) of the electrons (laser photons). We find that the induced coherence substantially increases the cell current (photon flux) and therefore the power of the QHE. As in the laser QHE, quantum coherence in the photocell QHE results in the faster removal of electrons from the recombination region, so that we can reduce the a → b_1,2 transition and enhance the photocurrent α → β. This reduces recombination losses and increases the power delivered to the load. For example, in the limit of a weak pump, , appropriate for a photodetector, the signal power is doubled by quantum coherence^¶ (see Fig. 2B and C).It is important to note that effects of environmentally induced decoherence τ₂ on photocell power can be made small by proper cell design. For the typical case in which the phonon occupation number is large, Eq. 8 shows that the stimulated phonon absorption term dominates other possible decoherence channels (τ₂ effects) even when the environmental effect is substantial . As a result, one can have a photocell with P-V characteristics shown in Fig. 3B such that the noised induced quantum coherence is robust against environmental decoherence.^||To summarize: There exists a close analogy between the laser QHE pumped by hot photons and cooled by a lower temperature entropy sink and a photocell QHE that is driven by hot photons while the ambient heat reservoir serves as the lower temperature entropy sink (21). Furthermore, we have shown that quantum interference can enhance laser and PV thermodynamic power beyond the limit of a system, which does not possess quantum coherence. Moreover, coherence generated by noise-induced quantum interference is essentially different from the quantum coherence produced by an external microwave field (9), which costs energy. In the present paper, quantum coherence is generated by the photocurrent due to quantum interference. No additional energy source is necessary to create such induced coherence. Nevertheless, as we have shown, the induced coherence can, in principle, enhance the efficiency of photovoltaic devices such as solar cells and/or photodetectors. We note that in the case of solar cells, the power generated^** is always less than the incident power times the Carnot factor—i.e., . In the case of photodetector operating at low temperature the phase coherence time T₂ can be relatively long, and applications of the present work to photodetection near at hand. Practical application to solar cell systems is possible but requires further research. However it is clear that the ultimate “in principle” limit of such devices is an important question of fundamental interest.     

Duodenal hematoma: the ring sign in MR imaging

Proper management of duodenal hematoma requires that an accurate diagnosis be made using noninvasive radiological methods. Conventional imaging may be nonspecific if there is no history of trauma or coagulopathy. Two cases of duodenal hematoma that were imaged by magnetic resonance (MR) and computed tomography (CT) are described. In both cases the hematoma had a well-defined concentric ring configuration on MR images, a finding which helped establish the diagnosis. MR imaging may provide tissue-specific characterization of duodenal hematomas.     

Giant-cell reparative granuloma of the hand and foot bones

Giant-cell reparative granuloma (GCRG) is an uncommon benign reactive intraosseous lesion. It occurs in the skull, jaw, hand, foot, and facial bones and rarely in other skeletal sites. It is a solitary, lytic, expanded lesion and infrequently may extend into the surrounding soft tissue. Histologically, it is composed of fibrous stroma with spindle-shaped fibroblasts, multinucleated giant cells, and inflammatory mononuclear cells. Areas of hemorrhage are uniformly present. It may be difficult to distinguish this entity from an aneurysmal bone cyst, giant-cell tumor, or brown tumor of hyperparathyroidism because of roentgenographic and histologic similarities. Accurate diagnosis is essential for appropriate treatment; serum calcium, phosphorus, and parathyroid hormone levels should be measured. Curettage and bone graft are effective treatments for both primary lesions and recurrences. Second recurrences are rare.     

Mitogen-activated protein kinases, inhibitory-kappaB kinase, and insulin signaling in human omental versus subcutaneous adipose tissue in obesity

MAPKs and inhibitory-kappaB kinase (IKK) were suggested to link various conditions thought to develop in adipose tissue in obesity (oxidative, endoplasmic reticulum stress, inflammation) with insulin resistance. Yet whether in obesity these kinases are affected in a fat-depot-differential manner is unknown. We assessed the expression and phosphorylation of these kinases in paired omental and abdominal-sc fat biopsies from 48 severely obese women (body mass index > 32 kg/m(2)). Protein and mRNAs of p38MAPK, ERK, c-Jun kinase-1, and IKKbeta were increased 1.5-2.5-fold in omental vs. sc fat. The phosphorylated (activated) forms of these kinases were also increased to similar magnitudes as the total expression. However, phosphorylation of insulin receptor substrate-1 on Ser312 (equivalent of murine Ser307) was not increased in omental, compared with sc, fat. Consistently, fat tissue fragments stimulated with insulin demonstrated that tyrosine phosphorylation and signal transduction to Akt/protein kinase B in omental fat was not inferior to that observable in sc fat. Comparison with lean women (body mass index 23.2 +/- 2.9 kg/m(2)) revealed similar ERK2 and IKKbeta expression and phosphorylation in both fat depots. However, as compared with lean controls, obese women exhibited 480 and 270% higher amount of the phosphorylated forms of p38MAPK and c-Jun kinase, respectively, in omental, but not sc, fat, and this expression level correlated with clinical parameters of glycemia and insulin sensitivity. Increased expression of stress-activated kinases and IKK and their phosphorylated forms in omental fat occurs in obesity, potentially contributing to differential roles of omental and sc fat in the pathophysiology of obesity.     

Differences in characteristics of patients with and without known risk factors for hepatocellular carcinoma in the United States

AIM： To examine the clinical characteristics of a subgroup of patients with hepatocellular carcinoma （HCC） and compare them to those with known risk factors. METHODS： We used the HCC database of 306 patients seen at our institution from January 1, 1995 to December 31, 2001. Of the 306 patients, 63 （20%, group 1） had no known risk factors （hepatitis C virus, hepatitis B virus, alcohol, hemochromatosis or cirrhosis from any cause） and 243 （group 2） had one or more risk factors. RESULTS： The median age was similar in both groups, but there were disproportionate numbers of younger （〈 30 years old）, older （〉 80 years） patients, women （33% vs 18%）, and Caucasians （81% vs 52%） in group 1 as compared to group 2. There were fewer Asians （2% vs 11%） and African Americans （13% vs 27%） in group 1. Abdominal pain （70% vs 37%） was more common while gastrointestinal bleeding （0% vs 11%） and ascites （4% vs17%） were less common in group i compared to group 2. Group 1 had larger tumor burden （median size 9.4 cm vs 5.7 cm） at the time of presentation, but there were no differences in the site （right, left or bilateral lesions）, or number of tumors between the two groups. CONCLUSION： HCC patients without identifiable risk factors have different characteristics and clinical presentation compared to those with known risk factors.Absence of cirrhosis and larger tumor burden may explain the differences in the presenting symptoms.     

A diffusion of innovations approach to gerontological curriculum enrichment: institutionalizing and sustaining curricula change

This article describes a gerontological enrichment model for institutionalizing and sustaining curricular change utilizing Rogers' (1995, 2003) diffusion of innovations approach to organizational change. The goal of the project, funded by the John A. Hartford Foundation, is to transform the social work curriculum at a major state university so that age and intergenerational connections are important organizing principles in the diversity emphasis of the program. Components of the model include: (1) increasing faculty competence; (2) infusing gerontological/ geriatric competencies into all foundation courses; (3) community partner involvement; (4) intergenerational service-learning; (5) developing field and practicum sites; and (6) evaluation. Implications for gerontological/ geriatric education are discussed.     

The pharmacodynamic properties of azithromycin in a kinetics-of-kill model and implications for bacterial conjunctivitis treatment

Introduction

Antibiotics have traditionally been classified as bactericidal or bacteriostatic. Azithromycin belongs to the parent class of macrolides that are characteristically bacteriostatic. Some evidence suggests that this mol-ecule demonstrates bactericidal kill and has concentration-dependent effects. This study tests the hypothesis that azithromycin demonstrates a bactericidal, concentration-dependent antibiotic effect at concentrations corresponding to and exceeding published tear and conjunctival levels.

Methods

The antibacterial activity of different concentrations of azithromycin 1% in DuraSite® (AzaSite®; Inspire Pharmaceuticals Inc, Durham, NC, USA) was evaluated using a kinetics-of-kill model. Recent conjunctivitis isolates of Staphylococcus aureus, Streptococcus pneumoniae or Haemophilus influenzae were exposed to four concentrations of azithromycin (100, 250, 500 and 750 μg/ml). Starting concentrations were similar to the maximum concentrations (Cmax) that have been demonstrated in conjunctiva (83 μg/g) and tears (288 μg/ml) following topical ocular administration. The percentage of surviving bacteria at 30 and 60 minutes following exposure to each concentration were determined.

Results

Azithromycin failed to demonstrate bactericidal activity (i.e. a 3-log reduction in surviving bacteria) against S. aureus, S. pneumoniae or H. influenzae. Furthermore, the rate and extent of antibacterial activity with azithromycin did not change with higher concentrations, even at the highest tested concentration of 750 μg/ml.

Conclusion

Similar to the parent macrolide class, azithromycin demonstrates bacteriostatic activity against common conjunctival pathogens up to the maximum tested concentration of 750 μg/ml (i.e. 2.6-times and 9-times published Cmax tear and conjunctival concentration, respectively). Azithromycin’s bacteriostatic effects and prolonged elimination half-life will likely lead to a corresponding increase in the emergence of macrolide-resistant isolates.

     

The Irreversible Inhibition of Differentiation of Limb-Bud Mesenchyme by Bromodeoxyuridine

Growing freshly dissociated chick-limb bud cells (stage 24) over agar for 48 hr permits differentiation into cartilage upon monolayer culture even when initial plating and subculture densities are well below confluency. Addition of 5-bromodeoxyuridine (BrdU) during the initial (48-hr) period over agar irreversibly inhibits chondrogenic differentiation, as characterized by morphology, metachromasia, and sulfate incorporation into acid mucopolysaccharide. Simultaneous, but not subsequent, addition of excess thymidine will prevent the effect of the analogue. Collagen synthesis is not depressed in BrdU-treated cells. Radioautographic studies demonstrate the specific localization of BrdU in the nucleus. Treatment of trichloroacetic acid-precipitable material containing tritiated bromodeoxyuridine with deoxyribonuclease solubilizes 90% of the radioactivity. The loss of the analogue from this precipitable material upon prolonged culture of limb-bud cells is more rapid than can be expected from cell division alone. 5-Bromodeoxyuridine may affect a fraction of DNA involved in stabilization of the differentiated cell phenotype.