Mitochondrial localization of functional ferrochelatase from Plasmodium falciparum

In the malarial parasite, enzymes of heme-biosynthetic pathway are distributed in different cellular compartments. The site of localization of ferrochelatase in the malarial parasite is crucial, since it will decide the ultimate site of heme synthesis. Earlier results have differed in terms of localization, being the mitochondrion or apicoplast and the functional enzyme has not been cloned, expressed and characterized. The present study reveals that Plasmodium falciparum ferrochelatase (PfFC) gene encodes multiple transcripts of which the one encoding the full length functional protein (PfFC) has been cloned and the recombinant protein over-expressed and purified from E. coli cells. The enzyme shows maximum activity with iron, while zinc is a poor substrate. Immunofluorescence studies with antibodies to functional ferrochelatase reveal that the native enzyme is localized to the mitochondrion of the parasite indicating that this organelle is the ultimate site of heme synthesis.

ESR Study of a Cr5+ Centre in Ferroelectric Ammonium Sulphate

X-band electron spin resonance (ESR) studies of (CrO4)2- doped, X-irradiated single crystals of ferroelectric ammonium sulphate ((NH4)2SO4, TC = 223 K) at 300 and 208 K are reported. The paramagnetic centre responsible for the ESR spectrum is identified to be Cr5+. Superhyperfine interaction of the unpaired electron with two equivalent protons is observed. The spin-Hamiltonian parameters which are nearly axial at 300 K, with g < g indicating a dx2-y2 orbital ground state, acquired rhombic character below TC indicating a distortion of the sulphate tetrahedron. An increase in the value of the proton superhyperfine constant in the ferroelectric phase is indicative of stronger hydrogen bonding.

The pulse response of non-linear third order systems

The response of a third order non-linear system subjected to a pulse excitation is analysed. A transformation of the displacement variable is effected. The transformation function chosen is the solution of the linear problem subjected to the same pulse. With this transformation the equation of motion is brought into a form in which the method of variation of parameters is applicable for the solution of the problem. The method is applied to a single axis gyrostabilized platform subjected to an exponentially decaying pulse. The analytical results are compared with digital and analog computer solutions.

Electrophysiological correlates of hanseniasis

Sensory nerve action potentials (SNAPs) and compound nerve action potentials (CNAPs) were recorded from 25 normal subjects and 21 hanseniasis patients following electrical stimulation of the median nerve at the wrist. The various nerve conduction parameters from the affected nerves of the patients were compared with those from the clinically normal nerves of patients as well as data from healthy individuals. Analysis of the data and clinical correlation studies indicate the suitability of amplitudes of the SNAPs and CNAPs rather than the nerve conduction velocities in better characterizing the neuropathy of the patients. Significantly reduced amplitudes of responses from clinically unaffected nerves of patients indicate an early stage of neuropathy, thus being of predictive value. Further, a discriminant classifier, trained on data from clinically affected nerves of patients, classified most of the data from clinically unaffected nerves of patients as abnormal. This indicates that clinical neurophysiological studies can reveal leprous neuropathy much before it becomes clinically evident by means of sensory or motor loss. A discriminant score involving only the parameters of motor threshold, amplitude of digit potential and palm nerve conduction velocity is able to classify almost all of the normal and abnormal responses. The authors hope that further confirmative studies might ultimately lead to the use of the study of distal sensory conduction in the upper limbs in possible screening of a population exposed to Mycobacterium leprae. On the other hand, misclassification of a normal person occurred and suggests that further refinement of the methods is necessary in order to facilitate wider use of the methods under held conditions.

A CD8(+) T cell clone specific for antigen also recognizes peptidomimics present in anti-idiotypic antibody: Implications for T cell memory

The relay hypothesis [R. Nayak, S. Mitra-Kaushik, M.S. Shaila, Perpetuation of immunological memory: a relay hypothesis, Immunology 102 (2001) 387-395] was earlier proposed to explain perpetuation of immunological memory without requiring long lived memory cells or persisting antigen. This hypothesis envisaged cycles of interaction and proliferation of complementary idiotypic B cells (Burnet cells) and anti-idiotypic B cells (Jerne cells) as the primary reason for perpetuation of immunological memory. The presence of pepti-domimics of antigen in anti-idiotypic antibody and their presentation to antigen specific T cells was postulated to be primary reason for perpetuation of T cell memory. Using a viral hemagglutinin as a model, in this work, we demonstrate the presence of peptidomimics in the variable region of ail anti-idiotypic antibody capable of functionally mimicking the antigen derived peptides. A CD8(+) CTL clone was generated against the hemagglutinin protein which specifically responds to either peptidomimic synthesizing cells or peptidomimic pulsed antigen presenting cells. Thus, it appears reasonable that a population of activated antigen specific T cells is maintained in the body by presentation of peptidomimic through Jerne cells and other antigen presenting cells long after immunization. (C) 2007 Elsevier Inc. All rights reserved.

Conformation of di-n-propylglycine residues (Dpg) in peptides: crystal structures of a type I-turn forming tetrapeptide and an -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 -helical conformations stabilized by 11 successive 5 1 hydrogen bonds. In addition, a single 4 1 hydrogen bond is also observed at the N-terminus. All five Dpg residues adopt backbone torsion angles (, ) in the helical region of conformational space. Evaluation of the available structural data on Dpg peptides confirm the correlation between backbone bond angle NCC() and the observed backbone , values. For > 106° , helices are observed, while fully extended structures are characterized by < 106° . The mean values for extended and folded conformations for the Dpg residue are 103.6° ± 1.7° and 109.9° ± 2.6° , respectively.

Coordination polymers and hybrid networks of different dimensionalities formed by metal sulfites

In our effort to explore the use of the sulfite ion to design hybrid and open-framework materials, we have been able to prepare, under hydrothermal conditions, zero-dimensional [Zn(C12H8N2)(SO3)]center dot 2H(2)O, I (a = 7.5737(5) angstrom, b = 10.3969(6) angstrom, c = 10.3986(6) angstrom, alpha = 64.172(1)degrees, beta = 69.395(1)degrees, gamma = 79.333(1)degrees, Z = 2, and space group P (1) over bar), one-dimensional [Zn-2(C12H8N2)(SO3)(2)(H2O)], II (a = 8.0247(3) angstrom, b = 9.4962(3) angstrom, c = 10.2740(2) A, alpha = 81.070(1)degrees, beta = 80.438(1)degrees, gamma = 75.66(5)degrees, Z = 2, and space group P (1) over bar), two-dimensional [Zn-2(C10H8N2)(SO3)(2)]center dot H2O, III (a = 16.6062(1) angstrom, b = 4.7935(1) angstrom, c = 19.2721(5) angstrom, beta = 100.674(2)degrees, Z = 4, and space group C2/c), and three-dimensional [Zn-4(C6H12N2)(SO3)(4)(H2O)(4)], IV (a = 11.0793(3) angstrom, c = 8.8246(3) angstrom, Z = 2, and space group P42nm), of which the last three are coordination polymers. A hybrid open-framework sulfite-sulfate of the composition [C2H10N2][Nd(SO3)(SO4)(H2O)](2), V (a = 9.0880(3) angstrom, b = 6.9429(2) angstrom, c = 13.0805(5) A, beta = 91.551(2)degrees, Z = 2, and space group P2(1)/c), with a layered structure containing metal-oxygen-metal bonds has also been described.

Functional interaction of diphenols with polyphenol oxidase - Molecular determinants of substrate/inhibitor specificity SO FEBS JOURNAL

Polyphenol oxidase (PPO) catalyzes the oxidation of o-diphenols to their respective quinones. The quinones autopolymerize to form dark pigments, an undesired effect. PPO is therefore the target for the development of antibrowning and antimelanization agents. A series of phenolic compounds experimentally evaluated for their binding affinity and inhibition constants were computationally docked to the active site of catechol oxidase. Docking studies suggested two distinct modes of binding, dividing the docked ligands into two groups. Remarkably, the first group corresponds to ligands determined to be substrates and the second group corresponds to reversible inhibitors. Analyses of the complexes provide structural explanations for correlating subtle changes in the position and nature of the substitutions on o-diphenols to their functional properties as substrates and inhibitors. Higher reaction rates and binding are reckoned by additional interactions of the substrates with key residues that line the hydrophobic cavity. The docking results suggest that inhibition of oxidation stems from an interaction between the aromatic carboxylic acid group and the apical His 109 of the four coordinates of the trigonal pyramidal coordination polyhedron of CuA. The spatial orientation of the hydroxyl in relation to the carboxylic group either allows a perfect fit in the substrate cavity, leading to inhibition, or because of a steric clash flips the molecule vertically, facilitating oxidation. This is the first study to explain, at the molecular level, the determinants Of substrate and inhibitor specificity of a catechol oxidase, thereby providing a platform for the design of selective inhibitors useful to both the food and pharmaceutical industries.

Exfoliation of alpha-hydroxides of nickel and cobalt in water

p-Aminobenzoate ion intercalated alpha-hydroxides of nickel/cobalt were synthesized by precipitation using ammonia (pH = similar to 12). Aqueous colloidal suspension of alpha-hydroxide of nickel/cobalt was obtained on washing the precipitate as the pH was reduced to similar to 7. The development of partial positive charge on the amine end of the intercalated anion causes repulsion between the layers leading to exfoliation and colloidal suspension of monolayers in water. While theb layers could be restacked from the colloidal suspension in the presenceof other anions in the case of alpha-cobalt hydroxide, the exfoliation could not be reversed easily in the case of the nickel analog. (C) 2010 Elsevier Inc. All rights reserved.

Dielectric, Ferroelectric and Relaxor Behavior of BaLaxBi4-xTi4O15 Ceramics

Monophasic BaLaxBi4-xTi4O15 (x = 0, 0.2, 0.4, 0.6 and 0.8) ceramics, fabricated from the powders synthesized via the solid-state reaction route exhibited relaxor behavior. Dielectric properties of the well sintered ceramics were measured in a wide frequency range (1 kHz-1 MHz) at different temperatures (300-750 K). The temperature of dielectri maximum (T-m) was found to decrease significantly from 696 K for an undoped sample (x = 0) to 395 K for the sample corresponding to the composition x = 0.8 accompanied by a decrease in the magnitude ofdielectric maximum (epsilon(m)). The temperature variation of the dielectric constant on the high temperature slope of the peak (T > T-m) was analyzed by using the Lorentz-ype quadratic law and the diffuseness of the peak was found to increase with increasing x. Vogel-Fulcher modelling of dielectric relaxation showed a decrease in freezing temperature (T-VF) (from 678 to 340 K) and an increase in the activation energy (5 to 24 meV) for the frequency dispersion with increase in x (La-3 divided by content). Strength of frequency dispersion of the phase transition increased with lanthanum content. Polarization (P)-electric field (E) hysteresis loops recorded at 373 showed a transition from a nearly squarish to slim loop hysteresis behavior with increasing lanthanum content.

Synthetic and conformational studies on dehydroalanine-containing model peptides

Three model dipeptides containing a dehydroalanine residue (Ala) at the C-terminal, Boc-X-Ala-NHCH3 [X = Ala, Val, and Phe,] have been synthesized and their solution conformations investigated by 1H-NMR, IR, and CD spectroscopy. NMR studies on these peptides in CDCl3 clearly indicate that the NH group of dehydroalanine is involved in an intramolecular hydrogen bond. This conclusion is supported by IR studies also. Nuclear Overhauser effect (NOE) studies are also accommodative of an inverse -turn-type of conformation that is characterised by conformational angles of -70° and +70° around the X residue, and a C[stack i+1 ]H-Ni+2H interproton distance of 2.5 Å. It appears that unlike dehydrophenylalanine or dehydroleucine, which tend to stabilize -turn type of structures occupying the i + 2 position of the turn, dehydroalanine favors the formation of an inverse -turn, centered at the proceeding L-residue in such solvents as CDCl3 and (CD3)2SO. A comparison of solution conformation of Boc Val-Ala-NHCH3 with the corresponding saturated analogue, Boc-Val-Ala-NHCH3, is also presented and shows that dehydroalanine is responsible for inducing the turn structure. It may be possible to design peptides with different preferred conformations using the suitable dehydroamino acid.

Studies on structural and electrical properties of sprayed SnO2 : Sb films

Thin films of antimony-doped tin oxide (SnO2:Sb) were prepared by spray pyrolysis using stannous chloride (SnCl2) and antimony trichloride (SbCl3) as precursors. The antimony doping was varied from 0 to 4 wt%. Scanning electron microscopy (SEM) revealed the surface morphology to be very smooth, yet grainy in nature. X-ray diffraction (XRD) shows films to have preferred orientation, which varies with the extent of antimony doping: undoped films prefer the (2 1 1) orientation, while the (3 0 1) orientation is preferred for doping levels of 0.5 and 1.0 wt%. For higher doping levels, the (2 0 0) orientation is preferred. This difference in preferred orientations is reflected in the SEM of the films. Atomic force microscopy (AFM) reveals that film roughness is not affected by antimony doping. The minimum sheet resistance (2.17 ohm/square) achieved in the present study is lower than values reported to date in SnO2:Sb films prepared from SnCl2 precursor. The Hall mobility of undoped SnO2 films was found to be 109.52 cm(2)/V s, which reduces to 2.55 cm(2)/ Vs for the films doped with 4 wt% of Sb. On the other hand, the carrier concentration, which is 1.23 x 10(19) cm(-3) in undoped films, increases to 2.89 x 10(21) cm(-3) for the films doped with 4 wt% of Sb. (c) 2004 Elsevier B.V. All rights reserved.

Conformation of di-n-propylglycine residues (Dpg) in peptides: crystal structures of a type I 'beta-turn forming tetrapeptide and an alpha-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' beta-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 alpha-helical conformations stabilized by 11 successive 5 -> 1 hydrogen bonds. In addition, a single 4 -> 1 hydrogen bond is also observed at the N-terminus. All live Dpg residues adopt backbone torsion angles (phi, psi) 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-alpha-C' (tau) and the observed backbone phi,psi values. For tau > 106 degrees, helices are observed, while fully extended structures are characterized by tau < 106 degrees. The mean r values for extended and folded conformations for the Dpg residue are 103.6 degrees +/- 1.7 degrees and 109.9 degrees +/- 2.6 degrees, respectively. Copyright (C) 2007 European Peptide Society and John Wiley & Sons, Ltd.

Large deflections of rectangular plates

Approximate solutions for the non-linear bending of thin rectangular plates are presented considering large deflections for various boundary conditions. In the case of stress-free edges, solutions are given for von Kármán's equations in terms of the stress function and the deflection of the plate. In the case of immovable edges, equations are constructed in terms of the three displacements and these are solved. The solution is given by using double series consisting of the appropriate Beam Functions which satisfy the boundary conditions. The differential equations are satisfied by using the orthogonality properties of the series. Numerical results for square plates with uniform lateral load indicate good convergence of the series solution presented here.

Characterization of two M17 family members in Escherichia coli, Peptidase A and Peptidase B

Escherichia coil encodes two aminopeptidases belonging to the M17 family: Peptidase A (PepA) and Peptidase B (PepB). To gain insights into their substrate specificities, PepA or PepB were overexpressed in Delta pepN, which shows greatly reduced activity against the majority of amino acid substrates. Overexpression of PepA or PepB increases catalytic activity of several aminopeptidase substrates and partially rescues growth of Delta pepN during nutritional downshift and hightemperature stress. Purified PepA and PepB display broad substratespecificity and Leu, Lys, Met and Gly are preferred substrates. However, distinct differences are observed between these two paralogs: PepA is more stable at high temperature whereas PepB displays broader substrate specificity as it cleaves Asp and insulin B chain peptide. Importantly, this strategy, i.e. overexpression of peptidases in Delta pepN and screening a panel of substrates for cleavage, can be used to rapidly identify peptidases with novel substrate specificities encoded in genomes of different organisms. (C) 2010 Elsevier Inc. All rights reserved.