The interaction of glycoxylate with cysteine and its application to the assay of isocitritase and of transaminases involving glyoxylate

An interesting interaction between glyoxylate and cystein takes place in phosphate buffer (pH 7.0) to form a product which is resistant to hydrolysis at ordinary temperatures. The reaction product is broken up by acid hydrolysis at elevated temperatures under controlled conditions, giving a quantitive yield of glyoxylate. Other keto acids, such as α-ketoglutarate, pyruvate and oxaloacetate, do not interact with cysteine under similar conditions. Methods based on these findings are described for(a) direct estimation of other keto acids in the presence of glyoxylate, and (b) assay of isocitritase and glyoxylate transaminase.

Interaction of heterocyclic thiols/thiones eliminated from cephalosporins with iodine and its biological implications

Hydrolysis of beta-lactam antibiotics by beta-lactamases (e. g., metallo-beta-lactamase, m beta l) is one of the major bacterial defense systems. These enzymes can catalyze the hydrolysis of a variety of antibiotics including the latest generation of cephalosporins, cephamycins and imipenem. It is shown in this paper that the thiol/thione moieties eliminated from certain cephalosporins by m beta l-mediated hydrolysis readily react with molecular iodine to produce ionic compounds having S-I bonds. While the reaction of MTT with iodine produced the corresponding disulfide, MDT and DMETT produced the charge-transfer complexes MDT-I-2 and DMETT-I-2, respectively. Addition of two equivalents of I-2 to MDT produced a novel cationic complex having an almost linear S-I+-S moiety and I-5(-) counter anion.However, this reaction appears to be highly solvent dependent. When the reaction of MDT with I2 was carried out in water, the reaction produced a monocation having I-5(-), indicating the reactivity of MDT toward I2 is very similar to that of the most commonly used antithyroid drug methimazole (MMI). In contrast to MMI, MDT and DMETT, the triazine-based compound MTDT acts as a weak donor toward iodine. (C)2010 Elsevier Ltd. All rights reserved.

A particle filtering approach for structural system identification in vehicle–structure interaction problems

The problem of identification of parameters of a beam-moving oscillator system based on measurement of time histories of beam strains and displacements is considered. The governing equations of motion here have time varying coefficients. The parameters to be identified are however time invariant and consist of mass, stiffness and damping characteristics of the beam and oscillator subsystems. A strategy based on dynamic state estimation method, that employs particle filtering algorithms, is proposed to tackle the identification problem. The method can take into account measurement noise, guideway unevenness, spatially incomplete measurements, finite element models for supporting structure and moving vehicle, and imperfections in the formulation of the mathematical models. Numerical illustrations based on synthetic data on beam-oscillator system are presented to demonstrate the satisfactory performance of the proposed procedure.

Folding a Polymer via Two-Point Interaction with an External Folding Agent: Use of H-Bonding and Charge-Transfer Interactions

A polymer containing electron-rich aromatic donors (1,5-dialkoxynaphthalene (DAN)) was coerced into a folded state by an external folding agent that contained an electron-deficient aromatic acceptor (pyromellitic diimide (PM)) unit. The donor-containing polymer was designed to carry a tertiary amine moiety in the linking segment, which served as an H-bonding site for reinforcing the interaction with the acceptor containing folding agent that also bore a carboxylic acid group. The H-bonding interaction of the carboxylic acid and the tertiary amine brings the PDI unit between two adjacent DAN units along the polymer backbone to induce charge-transfer (C-T) interactions, and this in turn causes the polymer chain to form a pleated structure. Evidence for the formation of such a pleated structure was obtained from NMR titration studies and also by monitoring the C-T band in their UV-visible spectra. By varying the length of the segment that links the PDI acceptor to the carboxylic acid group, we showed that the most effective folding agent was the one that had a single carbon spacer, as evident from the highest value of the association constant. Control experiments with propionic acid clearly demonstrated the importance of the additional C-T interactions for venerating the folded structures. Further, solution viscosity measurements in the presence of varying amounts of the folding agent revealed a gradual stiffening of the chain in the case of the PDI carrying carboxylic acid, whereas no such affect was seen in the case of simple propionic acid. These observations were supported by D FT calculations of the interactions of a dimeric model of the polymer with the various folding agents; here too the stability of the complex was seen to be highest in the case of the single carbon spacer.

The effects of abiotic and biotic factors on somatic embryogenesis and seedlings of Pinus sylvestris (L.)

Somatic embryogenesis (SE) is an asexual form of plant propagation that occurs in nature and mimics many of the events of sexual reproduction. Pinus sylvestris (L.) is an important source of timber in Northern Eurasia but it is recalcitrant to somatic embryogenesis. Several factors important for the success of the P. sylvestris embryogenic cultures have not been thoroughly investigated. In this study, we examined the effects of parental genotypes on the SE in P. sylvestris, the involvement of the gaseous plant growth regulator, ethylene in SE, and also biotic effects on somatic embryos as well as on seedlings. We tested parental effects on immature embryo initiation for different media, storage periods, and on the maturation process. Maternal effects were found to be crucial for SE in the absence of paternal effects. No maternal-paternal interaction was observed at any stage of somatic embryo production. Additionally the role of ethylene at different developmental stages of SE was investigated. Two ACC synthase genes, PsACS1 and PsACS2, were isolated and characterized. PsACS1 was expressed during the proliferation stage in all tested genotypes, whereas PsACS2 was only expressed in somatic embryos of each genotype. Ethylene production in embryos at stage 3 was significantly higher than the other stages. In a parallel study, the response of somatic embryos to fungal elicitors was investigated. Three fungi, a mutualistic ectomycorrhizal (ECM) fungus (Suillus bovinus), a weak Scots pine pathogen (Heterobasidion parviporum) and a strong pathogen (H. annosum) were used. The gene expression patterns for embryos exposed to the H. parviporum elicitor were found to be similar to that documented for S. bovinus among the tested genes. By contrast somatic embryos exposed to the H. annosum elicitor had a different pattern of regulation which was marked by a delayed response, and in some cases death of the embryos. Furthermore, interaction without direct contact between P. sylvestris seedlings and microbes (mutualistic and pathogenic fungus, cyanobacterium) were investigated. Several novel genes expressed in seedlings treated with ECM fungus were isolated which suggested that physical contact is not necessary for elicitation of host responses. The results suggest that somatic embryos and seedlings of P. sylvestris are genetically well equipped to respond to fungal elicitor/exudates and could serve as a suitable model for reproducible molecular studies in conifer tree patho- and symbiotic systems.

Studies on interaction of colloidal Ag nanoparticles with Bovine Serum Albumin (BSA)

Biofunctionalization of noble metal nanoparticles like Ag, Au is essential to obtain biocompatibility for specific biomedical applications. Silver nanciparticles are being increasingly used in bio-sensing applications owing to excellent optoelectronic properties. Among the serum albumins, the most abundant proteins in plasma, a wide range of physiological functions of Bovine Serum Albumin (BSA) has made it a model system for biofunctionalization. In absence of adequate prior reports, this study aims to investigate the interaction between silver nanoparticles and BSA. The interaction of BSA [0.05-0.85% concentrations] with Ag nanoparticles [50 ppm concentration] in aqueous dispersion was Studied through UV-vis spectral changes, morphological and surface structural changes. At pH 7, which is More than the isoelectric point of BSA, a decrease in absorbance at plasmon peak of uninteracted nanciparticles (425 mn) was noted till 0.45% BSA, beyond that a blue shift towards 410 urn was observed. The blue shift may be attributed to enhanced electron density on the particle surfaces. Increasing pH to 12 enhanced the blue shift further to 400 rim. The conformational changes in BSA at alkaline pH ranges and consequent hydrophobic interactions also played an important role. The equilibrium adsorption data fitted better to Freundlich isotherm compared to Langmuir Curve. The X-ray diffraction study revealed complete coverage of Ag nanoparticles by BSA. The scanning electron microscopic study of the interacted nanoparticles was also carried Out to decipher morphological changes. This study established that tailoring the concentration of BSA and pH of the interaction it was possible to reduce aggregation of nanoparticles. Biofunctionalized Ag nanoparticles with reduced aggregation will be more amenable towards bio-sensing applications. (C) 2009 Elsevier B.V. All rights reserved.

Structure-function relationships of icosahedral plant

X-ray diffraction studies on single crystals of a few viruses have led to the elucidation of their three dimensional structure at near atomic resolution. Both the tertiary structure of the coat protein subunit and the quaternary organization of the icosahedral capsid in these viruses are remarkably similar. These studies have led to a critical re-examination of the structural principles in the architecture of isometric viruses and suggestions of alternative mechanisms of assembly. Apart from their role in the assembly of the virus particle, the coat proteins of certian viruses have been shown to inhibit the replication of the cognate RNA leading to cross-protection. The coat protein amino acid sequence and the genomic sequence of several spherical plant RNA viruses have been determined in the last decade. Experimental data on the mechanisms of uncoating, gene expression and replication of several classes of viruses have also become available. The function of the non-structural proteins of some viruses have been determined. This rapid progress has provided a wealth of information on several key steps in the life cycle of RNA viruses. The function of the viral coat protein, capsid architecture, assembly and disassembly and replication of isometric RNA plant viruses are discussed in the light of this accumulated knowledge.

Kinetics and the mechanism of interaction of the endoplasmic reticulum chaperone, calreticulin, with monoglucosylated (Glc(1)Man(9)GlcNAc(2)) substrate

Calreticulin is a lectin-like molecular chaperone of the endoplasmic reticulum in eukaryotes. Its interaction with N-glycosylated polypeptides is mediated by the glycan, Glc(1)Man(9)GlcNAc(2), present on the target glycoproteins. In this work, binding of monoglucosyl IgG (chicken) substrate to calreticulin has been studied using real time association kinetics of the interaction with the biosensor based on surface plasmon resonance (SPR). By SPR, accurate association and dissociation rate constants were determined, and these yielded a micromolar association constant. The nature of reaction was unaffected by immobilization of either of the reactants. The Scatchard analysis values for K-a agreed web crith the one obtained by the ratio k(1)/k(-1). The interaction was completely inhibited by free oligosaccharide, Glc(1)Man(9)GlcNAc(2), whereas Man(9)GlcNAc(2) did not bind to the calreticulin-substrate complex, attesting to the exquisite specificity of this interaction. The binding of calreticulin to IgG was used for the development of immunoassay and the relative affinity of the lectin-substrate association was indirectly measured. The values are in agreement with those obtained with SPR. Although the reactions are several orders of magnitude slower than the diffusion controlled processes, the data are qualitatively and quantitatively consistent with single-step bimolecular association and dissociation reaction. Analyses of the activation parameters indicate that reaction is enthalpically driven and does not involve a highly ordered transition state. Based on these data, the mechanism of its chaperone activity is briefly discussed.