Studies on a-amylase inhibitors from seeds of sorghum bicolor

Six inhibitors (Slal, SIa2, SIa3, SIa4, SIa5 and SIa6) of a-amylase from mammalian, insect, bacterial and fungal sources were purified from seeds of Sorghum bicolor (L) Moench by saline extraction, precipitation with ammonium sulphate, affinity chromatography on Red Sepharose, preparative and analytical reverse phase HPLC on Vydac C(_18) columns. The complete primary structures of five of these inhibitors (Slal-5) were determined by automatic degradation of the intact, reduced and S-alkylated proteins and by manual DABITC/PITC microsequencing of peptides obtained from enzyme digests. The first three inhibitors consist of 47 (Slal) and 48 (SIa2, SIa3) amino acids with respective molecular weights of 5,396, 5,310. and 5384. These basic proteins (pi predictions above 8) were found to be highly homologous between themselves and with the recently isolated γ-hordothionin. γ(_1)-and γ(_2)-purothionins (Colilla et al., 1990; Mendez et al., 1990) and are, therefore, considered to be thionin-like inhibitors. Four disulphide bonds were identified and their positions determined in the sequence of Slal. It has been reported that the a-amylase inhibitory activity of thionins is due to competition for calcium ions which is the most important co-factor for this enzyme activity (Matsuura et al., 1984; Buisson et al., 1987). Calcium binding motifs have been located in the sequences of Slal, Sla2 and Sla3 and their structural significance has been investigated by molecular modelling.SIa4 and SIa5 which consist of 118 (MW 12,485) and 116 (MW 12,761) amino acids respectively are also basic polypeptides (pI predictions above 8). These proteins were found to be 35% homologous between themselves and showed significant homology (range 21-42%) with the members of the cereal superfamily. Hydrophobicity plots and secondary structure prediction results also revealed common features between these proteins and those of the cereal superfamily. Only a preliminary N-terminal sequence was obtained for Sla6 which was found to inhibit human salivary a-amylase and locust gut a-amylase

Dynamics of the symmetric eigenvalue problem with shift strategies

A common algorithm for the computation of eigenvalues of real symmetric tridiagonal matrices is the iteration of certain special maps $F_\sigma$ called shifted $QR$ steps. Such maps preserve spectrum and a natural common domain is ${\cal T}_\Lambda$, the manifold of real symmetric tridiagonal matrices conjugate to the diagonal matrix $\Lambda$. More precisely, a (generic) shift s \in \RR defines a map $F_s: {\cal T}_\Lambda \to {\cal T}_\Lambda$. A strategy \sigma: {\cal T}_\Lambda \to \RR specifies the shift to be applied at $T$ so that $F_\sigma(T) = F_{\sigma(T)}(T)$. Good shift strategies should lead to fast deflation: some off-diagonal coordinate tends to zero, allowing for reducing of the problem to submatrices. For topological reasons, continuous shift strategies do not obtain fast deflation; many standard strategies are indeed discontinuous. Practical implementation only gives rise systematically to bottom deflation, convergence to zero of the lowest off-diagonal entry $b(T)$. For most shift strategies, convergence to zero of $b(T)$ is cubic, $|b(F_\sigma(T))| = \Theta(|b(T)|^k)$ for $k = 3$. The existence of arithmetic progressions in the spectrum of $T$ sometimes implies instead quadratic convergence, $k = 2$. The complete integrability of the Toda lattice and the dynamics at non-smooth points are central to our discussion. The text does not assume knowledge of numerical linear algebra.Comment: 22 pages, 4 figures. This preprint borrows heavily from the unpublished preprint arXiv:0912.3376 but is adapted for a different audienc

An atlas for tridiagonal isospectral manifolds

Let ${\cal T}_\Lambda$ be the compact manifold of real symmetric tridiagonal matrices conjugate to a given diagonal matrix $\Lambda$ with simple spectrum. We introduce {\it bidiagonal coordinates}, charts defined on open dense domains forming an explicit atlas for ${\cal T}_\Lambda$. In contrast to the standard inverse variables, consisting of eigenvalues and norming constants, every matrix in ${\cal T}_\Lambda$ now lies in the interior of some chart domain. We provide examples of the convenience of these new coordinates for the study of asymptotics of isospectral dynamics, both for continuous and discrete time.Comment: Fixed typos; 16 pages, 3 figure

Probing protein sequences as sources for encrypted antimicrobial peptides

Starting from the premise that a wealth of potentially biologically active peptides may lurk within proteins, we describe here a methodology to identify putative antimicrobial peptides encrypted in protein sequences. Candidate peptides were identified using a new screening procedure based on physicochemical criteria to reveal matching peptides within protein databases. Fifteen such peptides, along with a range of natural antimicrobial peptides, were examined using DSC and CD to characterize their interaction with phospholipid membranes. Principal component analysis of DSC data shows that the investigated peptides group according to their effects on the main phase transition of phospholipid vesicles, and that these effects correlate both to antimicrobial activity and to the changes in peptide secondary structure. Consequently, we have been able to identify novel antimicrobial peptides from larger proteins not hitherto associated with such activity, mimicking endogenous and/or exogenous microorganism enzymatic processing of parent proteins to smaller bioactive molecules. A biotechnological application for this methodology is explored. Soybean (Glycine max) plants, transformed to include a putative antimicrobial protein fragment encoded in its own genome were tested for tolerance against Phakopsora pachyrhizi, the causative agent of the Asian soybean rust. This procedure may represent an inventive alternative to the transgenic technology, since the genetic material to be used belongs to the host organism and not to exogenous sources

Equivalent bosonic theory for the massive Thirring model with non-local interaction

We study, through path-integral methods, an extension of the massive Thirring model in which the interaction between currents is non-local. By examining the mass-expansion of the partition function we show that this non-local massive Thirring model is equivalent to a certain non-local extension of the sine-Gordon theory. Thus, we establish a non-local generalization of the famous Coleman's equivalence. We also discuss some possible applications of this result in the context of one-dimensional strongly correlated systems and finite-size Quantum Field Theories.Comment: 15 pages, latex, no figure

Mapping the depleted area of silicon diodes using a micro-focused X-ray beam

For the Phase-II Upgrade of the ATLAS detector at CERN, the current ATLAS Inner Detector will be replaced with the ATLAS Inner Tracker. The ATLAS Inner Tracker will be an all-silicon detector, consisting of a pixel tracker and a strip tracker. Sensors for the ITk strip tracker are required to have a low leakage current up to bias voltages of -700 V to maintain a low noise and power dissipation. In order to minimise sensor leakage currents, particularly in the high-radiation environment inside the ATLAS detector, sensors are foreseen to be operated at low temperatures and to be manufactured from wafers with a high bulk resistivity of several k{\Omega} cm. Simulations showed the electric field inside sensors with high bulk resistivity to extend towards the sensor edge, which could lead to increased surface currents for narrow dicing edges. In order to map the electric field inside biased silicon sensors with high bulk resistivity, three diodes from ATLAS silicon strip sensor prototype wafers were studied with a monochromatic, micro-focused X-ray beam at the Diamond Light Source. For all devices under investigation, the electric field inside the diode was mapped and its dependence on the applied bias voltage was studied. The findings showed that the electric field in each diode under investigation extended beyond its bias ring and reached the dicing edge

Reflexiones acerca de las cambiantes narrativas sobre las vacunas contra la COVID-19

Nos propusimos discernir en qué medida las estrategias mediáticas adoptadas en torno a las vacunas contra la covid-19, a lo largo de los primeros 15 meses desde el comienzo de su aplicación, pueden considerarse aportes legítimos y coherentes para comprender mejor su desempeño, y en qué grado las narrativas elaboradas pudieran responder a intereses económicos de las élites corporativas. Una vez recopilados los elementos más relevantes con que se configuran las narrativas predominantes desde el momento en que se concibieron las vacunas, se identificaron diversas anomalías que resultaron, en mayor o menor medida, invisibilizadas en el proceso de su aprobación y de los resultados de su aplicación. Las más significativas conciernen al manejo de las definiciones, los incumplimientos de compromisos y los conflictos de interés que comprometen la actuación de las empresas comercializadoras y los entes reguladores de las vacunas. Numerosos elementos relacionados con los intereses corporativos han gravitado en la elaboración del relato sobre las vacunas. Entre los que reclaman resignificación se hallan: su capacidad preventiva real de contagios, evoluciones graves y muertes, su eficacia ante nuevas variantes, la duración de la inmunidad que confieren, sus efectos adversos, el papel sinérgico de la inmunidad adquirida y los recursos empleados por las empresas para conseguir un predominio virtualmente monopólico en el mercado