XRD studies of polyurethane elastomers based on chitin/1,4-butane diol blends

Chitin based polyurethane elastomers (PUEs) were synthesized by step growth polymerization techniques using poly (ε-caprolactone) (PCL), 4, 4′- diphenylmethane diisocyanate (MDI) and blends of chitin and 1,4-butanne diol (BDO). The conventional spectroscopic characterization of the samples with FT-IR, ¹H NMR and ¹³C NMR were in accordance with proposed PUEs structure. The crystalline behavior of the synthesized polymers were investigated by X-ray diffraction (XRD), differential scanning calorimetery (DSC), optical microscopic technique and loss tangent curves (tan δ peaks). Results showed that crystallinity of the synthesized PUEs samples was affected by varying the chitin contents used as chain extender. The contents of chitin favors the formation of more ordered structure, as higher peak intensities were obtained from the PU extended with chitin than 1,4-butane diol (BDO). X-ray diffraction experiments results correlates with optical microscopy findings. The higher ΔH value; 41.57 (J g^?1) was found in the samples extended with chitin than BDO (31.32 J g^?1).     

Phosphatidic acid-mediated binding and mammalian cell internalization of the Vibrio cholerae cytotoxin MakA

Vibrio cholerae is a noninvasive intestinal pathogen extensively studied as the causative agent of the human disease cholera. Our recent work identified MakA as a potent virulence factor of V. cholerae in both Caenorhabditis elegans and zebrafish, prompting us to investigate the potential contribution of MakA to pathogenesis also in mammalian hosts. In this study, we demonstrate that the MakA protein could induce autophagy and cytotoxicity of target cells. In addition, we observed that phosphatidic acid (PA)-mediated MakA-binding to the host cell plasma membranes promoted macropinocytosis resulting in the formation of an endomembrane-rich aggregate and vacuolation in intoxicated cells that lead to induction of autophagy and dysfunction of intracellular organelles. Moreover, we functionally characterized the molecular basis of the MakA interaction with PA and identified that the N-terminal domain of MakA is required for its binding to PA and thereby for cell toxicity. Furthermore, we observed that the ΔmakA mutant outcompeted the wild-type V. cholerae strain A1552 in the adult mouse infection model. Based on the findings revealing mechanistic insights into the dynamic process of MakA-induced autophagy and cytotoxicity we discuss the potential role played by the MakA protein during late stages of cholera infection as an anti-colonization factor.     

A chromatographic technique (sephadex LH-20) for the separation of major prostaglandins

A chromatographic system for prostaglandins has been developed using a column containing LH-20 sephadex. Different degrees of resolution are possible by altering the fraction of methanol in methylenechloride. A 80 × 1 cm column with 5% methanol:CH₂Cl₂ separates the major classes A, E, F. 2% methanol:CH₂Cl₂ separates A₁ from A₂ and B₂. Experience with LH-20 sephadex suggests its value in terms of reproducibility, recovery, speed, and evidence for low blank readings in a radioimmunoassay.     

High regeneration rates in anther culture of interspecific sunflower hybrids

Optimization of anther culture with regard to the induction of callus formation and direct embryogenesis was obtained for interspecific hybrids ofH. annuus withH. tuberosus, H. laetiflorus, andH. resinosus by investigating six different induction media and four regeneration media. One media combination (MS-13, MS-R3 and MS-R4) used under different culture conditions (30°C / 35°C and different dark treatments) gave up to 92.7% embryogenic anthers with an average of 8.5 embryos per anther. However, direct embryogenesis as well as callus formation showed a strong genotypec and treatment specific reaction. From 5,600 anthers of the four investigated genotypes more than 2,000 plants could be regenerated. Regenerants were characterized by morphological traits and isozyme analyses to prove their androgenetic origin.     

An improved method for the simultaneous determination of photosynthetic O2 evolution and CO2 consumption in Rhizophora mucronata leaves

The photosynthetic gas-exchange has been assessed traditionally either as O₂ evolution or CO₂ consumption. In this study, we used a liquid-phase O₂ electrode combined with CO₂ optodes to examine simultaneously photosynthesis in intact leaves of mangrove Rhizophora mucronata. We verified suitable conditions for leaf photosynthetic rates by assessing pH levels and NaHCO₃ concentrations and compared these to the gas-exchange method at various PAR levels. The photosynthetic rate in response to pH exhibited a similar pattern both for O₂ evolution and CO₂ consumption, and higher rates were associated with intermediate pH compared with low and high pH values. The net photosynthetic quotient (PQ) of R. mucronata leaves ranged from 1.04–1.28. The PQ values, which were never lesser than 1, suggested that photorespiration did not occur in R. mucronata leaves under aqueous conditions. The similar maximum photosynthetic rates suggested that all measurements had a high capacity to adjust the photosynthetic apparatus under a light saturation condition. The simultaneous measurements of O₂ evolution and CO₂ consumption using the Clark oxygen electrode polarographic sensor with the CO₂ optode sensor provided a simple, stable, and precise measurement of PQ under aqueous and saturated light conditions.     

Protection of the photosynthetic apparatus against dehydration stress in the resurrection plant Craterostigma pumilum

The group of homoiochlorophyllous resurrection plants evolved the unique capability to survive severe drought stress without dismantling the photosynthetic machinery. This implies that they developed efficient strategies to protect the leaves from reactive oxygen species (ROS) generated by photosynthetic side reactions. These strategies, however, are poorly understood. Here, we performed a detailed study of the photosynthetic machinery in the homoiochlorophyllous resurrection plant Craterostigma pumilum during dehydration and upon recovery from desiccation. During dehydration and rehydration, C. pumilum deactivates and activates partial components of the photosynthetic machinery in a specific order, allowing for coordinated shutdown and subsequent reinstatement of photosynthesis. Early responses to dehydration are the closure of stomata and activation of electron transfer to oxygen accompanied by inactivation of the cytochrome b₆f complex leading to attenuation of the photosynthetic linear electron flux (LEF). The decline in LEF is paralleled by a gradual increase in cyclic electron transport to maintain ATP production. At low water contents, inactivation and supramolecular reorganization of photosystem II becomes apparent, accompanied by functional detachment of light‐harvesting complexes and interrupted access to plastoquinone. This well‐ordered sequence of alterations in the photosynthetic thylakoid membranes helps prepare the plant for the desiccated state and minimize ROS production.     

A laboratory study of the copper and nickel uptake and regulation in a copper-tolerant decapod, Cambarus bartoni (Fabricius) (Decapoda, Crustacea)

Tissue copper concentration in whole Cambarus bartoni, exposed for four weeks to 0.125, 0.25 and 0.5 mg Cu/litre and 0.2, 0.4 and 0.8 mg Ni/litre in the laboratory at 18 degrees C, showed a linear relationship with exposure time at 0.25 and 0.5 mg Cu/litre; the regression slope at 0.5 mg Cu/litre (r2 = 0.218; 0.001 less than P less than or equal to 0.05) was approximately two times higher than that at 0.25 mg Cu/litre (r2 = 0.148; 0.025 less than P less than or equal to 0.05). Regression analysis of nickel concentrations in whole crayfish as a function of exposure time showed a third degree polynomial relationship at 0.4 (y = 49.989 + 14.77x - 15.395x2 + 3.194x3) and 0.8 (y = 52.053 + 37.05x - 28.933x2 + 5.133x3) mg Ni/litre, as well as in the control (y = 49.126 + 27.253x - 23.468x2 + 4.168x3) (y = Ni concentration; x = exposure time in weeks), suggesting the occurrence of a Ni flux every 4 weeks.     

Efficacy of brain heart infusion-egg albumen agar,yeast extract phosphate agar and peptone glucose agar media for isolation of Blastomyces dermatitidis from sputum

The efficacy of brain heart infusion (BHI)-egg albumen agar, yeast extract phosphate agar and several modified peptone glucose agar media was evaluated for isolation of Blastomyces dermatitidis from sputum concomitantly seeded with the yeast form of the pathogen and Candida albicans. Based upon high per cent culture positivity of sputum, improved recovery (CFU/ml) of the seeded inoculum, faster growth rate of B. dermatitidis and low level of contamination, BHI-egg albumen agar, followed by yeast extract phosphate agar are recommended as the media of choice for the isolation of B. dermatitidis from contaminated clinical specimens.     

The Prolyl Peptidases PRCP/PREP Regulate IRS-1 Stability Critical for Rapamycin-induced Feedback Activation of PI3K and AKT

The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/AKT)/mammalian target of rapamycin (mTOR) pathway conveys signals from receptor tyrosine kinases (RTKs) to regulate cell metabolism, proliferation, survival, and motility. Previously we found that prolylcarboxypeptidase (PRCP) regulate proliferation and survival in breast cancer cells. In this study, we found that PRCP and the related family member prolylendopeptidase (PREP) are essential for proliferation and survival of pancreatic cancer cells. Depletion/inhibition of PRCP and PREP-induced serine phosphorylation and degradation of IRS-1, leading to inactivation of the cellular PI3K and AKT. Notably, depletion/inhibition of PRCP/PREP destabilized IRS-1 in the cells treated with rapamycin, blocking the feedback activation PI3K/AKT. Consequently, inhibition of PRCP/PREP enhanced rapamycin-induced cytotoxicity. Thus, we have identified PRCP and PREP as a stabilizer of IRS-1 which is critical for PI3K/AKT/mTOR signaling in pancreatic cancer cells.