Biochemical Studies on the Hemolymph Trypsin Inhibitors of the Tobacco Hornworm Manduca Sexta: A Thesis

Trypsin inhibitory activity from the hemolymph of the tobacco hornworm, Manduca sexta, was purified by affinity chromatography on immobilized trypsin and resolved into two fractions with molecular weights of 13700 (inhibitor A) and 8000 (inhibitor B) by Sephadex G-75 gel filtration. SDS-polyacrylamide gel electrophoresis under non-reducing conditions gave a molecular weight estimate of 15000 for inhibitor A and 8500 for inhibitor B. Electrophoresis of these inhibitors under reducing conditions on polyacrylamide gels gave molecular weight estimates of 8300 and 9100 for inhibitor A and inhibitor B, respectively, suggesting that inhibitor A is a dimer. Isoelectro-focusing on polyacrylamide gels focused inhibitor A as a single band with pI of 5.7, whereas inhibitor B was resolved into two components with pIs of 5.3 and 7.1. Both inhibitors A and B are stable at 100° C and at pH 1.0 for at least 30 minutes, but both are inactivated by dithiothreitol even at room temperature and non-denaturing conditions. Inhibitors A and B inhibit trypsin, chymotrypsin, plasmin, and thrombin but they do not inhibit elastase, papain, pepsin, subtilisin BPN\u27 and thermolysin. In fact, subtilisin BPN\u27 completely inactivated both inhibitors A and B. Inhibitor A and inhibitor B form stable complexes with trypsin. Stoichiometric studies showed that inhibitor A combines with trypsin and chymotrypsin in a 1:1 molar ratio. The inhibition constants (Ki) for trypsin and chymotrypsin inhibition by inhibitor A were estimated to be 1.45 x 10-8 M and 1.7 x 10-8M, respectively. Inhibitor A in complex with chymotrypsin does not inhibit trypsin (and vice versa) suggesting that inhibitor A has a common binding site for trypsin and chymotrypsin. The amino terminal amino acid sequences of inhibitors A and B revealed that both these inhibitors are homologous to the bovine pancreatic trypsin inhibitor (Kunitz) . Quantitation of the trypsin inhibitory activity in the hemolymph of the larval and the pupal stages of Manduca sexta showed that the trypsin inhibitory activity decreased from larval to the pupal stage. Further, inhibitor A at the concentration tested caused approximately 50% reduction in the rate of proteolytic activation of prophenoloxidase in a hemocyte lysate preparation from Manduca sexta, suggesting that inhibitor A may be involved in the regulation of prophenoloxidase activation. However, inhibitor B was not effective even at three times the concentration of inhibitor A. Since activation of prophenoloxidase has been suggested to resemble the activation of alternative pathway of complement, the effect of inhibitors A and B and the hemolymph of Manduca sexta on human serum alternative pathway complement activity was evaluated. The results showed that, although inhibitors A and B do not affect human serum alternative complement pathway, other proteinaceous component(s) in Manduca sexta hemolymph interact(s) and cause(s) an inhibition of human serum alternative complement pathway when tested using rabbit erythrocyte hemolytic assay

Analysis of secondary flow characteristics and hydrodynamic instability in fluid flow through curved ducts

This paper presents an investigation on the unique flow characteristics associated with fluid flow through curved ducts, which are fundamentally different to those in straight fluid passages. In curved ducts, the flow is subjected to centrifugal forces that induce counter-rotating vortices in the main axial fluid stream and give rise to spiralling fluid motion, commonly known as secondary flow. The study develops a novel three-dimensional computational fluid dynamics analysis whereby the laminar developing fluid flow in a curved rectangular duct is modelled. The flow characteristics are identified for a range of flow rates and duct aspect ratios at several duct curvatures. The contours of secondary flow and axial velocities are obtained to recognise the influence of flow/geometrical parameters on the secondary flow. Comparisons are made between the numerical predictions and the available experimental data. It is observed that, with increased duct flow rate, the secondary flow intensifies and beyond a certain critical flow condition, leads to hydrodynamic instability. The fluid flow structure is then significantly altered with the appearance of additional pair (or pairs) of vortices, termed as Dean Vortices, at the outer wall of the curved duct. This flow behaviour is also highly influenced by the duct aspect (height to width) ratio. The paper develops and presents a new approach for predicting the onset of Dean vortex generation

Parametric investigation of a synthetic jet heat sink for enhanced micro-scale heat transfer

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.This paper examines the characteristics of a pulsating fluid jet known as synthetic jet and its cooling effectiveness for heated micro fluid passages. The jet mechanism uses an oscillating diaphragm to inject a high-frequency fluid jet with a zero net mass flow through the jet orifice. The pulsed jet and the micro passage flow interaction is modelled as a 2- dimensional finite volume simulation with unsteady Reynolds­ averaged Navier-Stokes equations. For a range of conditions, the special characteristics of this periodically interrupted flow are identified while predicting the associated convective heat transfer rates. The results indicate that the pulsating jet leads to outstanding thermal performance in the micro passage increasing its heat dissipation by about 4.3 times compared to a micro passage without jet interaction within the tested parametric range. The degree of enhancement is first seen to grow gently and then rather rapidly beyond a certain flow condition to reach a steady value. The study also identifies the operational limits imposed by the fluid compressibility on the heat transfer characteristics. The proposed strategy has the unique intrinsic ability to generate outstanding degree of thermal enhancement in a micro passage without increasing its flow pressure drop. The technique is envisaged to have application potential in miniature electronic devices where localised cooling is desired over a base heat dissipation load.ksb201

Plant-derived antimicrobials to fight against multi-drug-resistant human pathogens

Antibiotic resistance is becoming a pivotal concern for public health that has accelerated the search for new antimicrobial molecules from nature. Numbers of human pathogens have inevitably evolved to become resistant to various currently available drugs causing considerable mortality and morbidity worldwide. It is apparent that novel antibiotics are urgently warranted to combat these life-threatening pathogens. In recent years, there have been an increasing number of studies to discover new bioactive compounds from plant origin with the hope to control antibiotic-resistant bacteria. This review attempts to focus and record the plant-derived compounds and plant extracts against multi-drug-resistant (MDR) pathogens including methicillin-resistant Staphylococcus aureus (MRSA), MDR-Mycobacterium tuberculosis and malarial parasites Plasmodium spp. reported between 2005 and 2015. During this period, a total of 110 purified compounds and 60 plant extracts were obtained from 112 different plants. The plants reviewed in this study belong to 70 different families reported from 36 countries around the world. The present review also discusses the drug resistance in bacteria and emphasizes the urge for new drugs

Particle Image Velocimetry and Infrared Thermography of Turbulent Jet Impingement on an Oscillating Surface

Jet impingement is widely used for forced-convection heat transfer applications and knowledge about its flow structure and heat transfer rate on a static surface are well established. However, the characteristics of jet impingement on an oscillating surface are relatively unknown. This study experimentally investigates the effect of surface oscillation on the fluid dynamics and heat transfer of an unconfined turbulent impinging jet. The Reynolds numbers of the axisymmetric jet are 5000 and 10,000, based on the jet-nozzle exit diameter, and the surface is placed at nominal standoff distances of 2 and 5 diameters from the jet-nozzle exit. The surface oscillates in a direction parallel to the jet axis at frequencies of 20 Hz and 50 Hz and at a peak-to-peak displacement amplitude of 0.2 times the jet-nozzle exit diameter. The phase-average and mean flow characteristics at six phases through the surface oscillation cycle, and the steady-state mean heat transfer rate at the oscillating surface, are determined using particle image velocimetry and infrared thermography respectively. These are analyzed and compared with the mean flow and heat transfer characteristics for jet impingement on a static surface. Surface oscillation directly affects the mean axial jet velocities and thence the mean radial velocities, and this effect is greater at locations in the flow-field closer to the surface. This gives rise to lower mean axial and radial strain rates in the impingement region and lower turbulence intensities in the wall-jet region when compared with those for a static surface. The frictional interaction between the impinging jet and oscillating surface induces higher surface temperatures than those on a static surface. These factors reduce the heat transfer rate for jet impingement on an oscillating surface when compared with that on a static surface. The reduction is greater in the impingement region than in the wall-jet region with the stagnation point Nusselt number for an oscillating surface being lower by a maximum value of 15%. Overall, for the range of parameters considered in this study, these findings suggest that surface oscillation in jet impingement weakens the transport phenomena capabilities from those present in the case of a static surface

Large-eddy simulations of a turbulent jet impinging on a vibrating heated wall

High-resolution large-eddy simulations (LES) are performed for an incompressible turbulent circular jet impinging upon a vibrating heated wall supplied with a constant heat flux. The present work serves to understand the flow dynamics and thermal characteristics of a turbulent jet under highly dynamic flow and geometric conditions. The baseline circular vibrating-wall jet impingement configuration undergoes a forced vibration in the wall-normal direction at the frequency, f = 100 Hz. The jet Reynolds number is = 23,000 and the nozzle-exit is at y/D = 2 where the wall vibrates between 0 and 0.5D with amplitude of vibration, A = 0.25D. The configuration is assembled through validation of sub-systems, in particular the method for generating the turbulent jet inflow and the baseline circular jet impingement configuration. Both time-mean and phase-averaged results are presented. The mean radial velocity increases upon positive displacement of the wall and decreases upon negative displacement but this correlation changes with increased radial distance from the stagnation point. Vortical structures are shown to play a major role in convective heat transfer even under the vibrating conditions of the impingement wall. Periodic shifts in the secondary Nusselt number peak are observed that depend upon the travelling eddy location and strength of large-eddy structures. Enhancement in heat transfer is seen in the stagnation region but this beneficial effect of vibration on heat transfer is confined to the impingement region, r/D < 1.5

Endophytic fungi and bioactive metabolites production: an update

Endophytic fungi are unique microbes that reside in the plant tissues and cause no harm or any symptoms of diseases. Although plants are the major source of modern drugs, there is a continuous search for new sources to obtain new lead molecules, with higher biological properties, for treating various diseases. Many plants are associated with several kinds of endophytic fungi capable of producing bioactive secondary metabolites. Thus, endophytic fungi can act as a reservoir of bioactive principles which are yet to be explored in detail. In addition, plant-endophytic fungal association stimulates plant growth, increase resistance towards phyto-pathogens, suppress the weed, and increase tolerance to abiotic and biotic stresses. In this chapter, various aspects of endophytic fungi including their symbiosis with plants, biological implications and important secondary metabolites production are discussed in detail. This information would certainly help to improve the pace of modern drug discovery

Convective heat transfer in airflow through a duct with wall thermal radiation

This paper presents a numerical investigation on airflow through a heated horizontal rectangular duct wherein the model considers the combined modes of natural and forced convection heat transfer and the thermal radiation from duct walls. The duct periphery is differentially heated with known temperature profiles imposed on the two opposite vertical sidewalls while the other two walls are treated as adiabatic. The air enters into the duct hydrodynamically fully developed and flows steadily under laminar conditions undergoing thermal development within the duct. Considering several temperature profiles on the two vertical sidewalls, the numerical simulation generates the heat transfer rates and associated fluid flow patterns in the duct for a range of airflow rates, duct aspect ratios and surface emissivity. The variation of local Nusselt number at duct walls and the fluid flow patterns are critically examined to identify thermal instabilities and the significance of wall thermal radiation effects on the overall heat transfer rates

Analysis of secondary flow characteristics and hydrodynamic instability in fluid flow through curved ducts

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.This paper presents an investigation on the unique flow characteristics associated with fluid flow through curved ducts, which are fundamentally different to those in straight fluid passages. In curved ducts, the flow is subjected to centrifugal forces that induce counter-rotating vortices in the main axial fluid stream and give rise to spiralling fluid motion, commonly known as secondary flow. The study develops a novel three-dimensional computational fluid dynamics analysis whereby the laminar developing fluid flow in a curved rectangular duct is modelled. The flow characteristics are identified for a range of flow rates and duct aspect ratios at several duct curvatures. The contours of secondary flow and axial velocities are obtained to recognise the influence of flow/geometrical parameters on the secondary flow. Comparisons are made between the numerical predictions and the available experimental data. It is observed that, with increased duct flow rate, the secondary flow intensifies and beyond a certain critical flow condition, leads to hydrodynamic instability. The fluid flow structure is then significantly altered with the appearance of additional pair (or pairs) of vortices, termed as Dean Vortices, at the outer wall of the curved duct. This flow behaviour is also highly influenced by the duct aspect (height to width) ratio. The paper develops and presents a new approach for predicting the onset of Dean vortex generation.mp201

Conformation of di-n-propylglycine residues (Dpg) in peptides: Crystal structures of a type I′β-turn forming tetrapeptide and an α-helical tetradecapeptide

The crystal structures of two oligopeptides containing di-n-propylglycine (Dpg) residues, Boc-Gly-Dpg-Gly-Leu-OMe (1) and Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (2) are presented. Peptide 1 adopts a type I-turn conformation with Dpg(2)-Gly(3) at the corner positions. The 14-residue peptide 2 crystallizes with two molecules in the asymmetric unit, both of which adopt &#945;-helical conformations stabilized by 11 successive 5 &#8594; 1 hydrogen bonds. In addition, a single 4 &#8594; 1 hydrogen bond is also observed at the N-terminus. All five Dpg residues adopt backbone torsion angles (&#966;,&#968;) in the helical region of conformational space. Evaluation of the available structural data on Dpg peptides confirm the correlation between backbone bond angle N-C&#945;-C'(&#950;) and the observed backbone &#966;,&#968;, values. For &#950; &gt; 106&#176;, helices are observed, while fully extended structures are characterized by &#950; &lt; 106&#176;. The mean values for extended and folded conformations for the Dpg residue are 103.6&#176; &#177; 1.7&#176; and 109.9&#176; &#177; 2.6&#176;, respectively