Biomagnetic measurements utilising a superparamagnetic marker: a feasibility study

Summary A preliminary study is here reported on a new potential marker for biomagnetic measurements. The marker consists of superparamagnetic polymer microspheres which were detected in the presence of external steady magnetic fields by means of an r.f.-SQUID magnetometer. The particles were prepared in samples differing in the concentration value and immersed in a homogeneous magnetic field of variable intensity. A simple model was taken into account for the distribution of the microspheres in the samples, so that the theoretical values were compared to the marker field values measured by the biomagnetic sensor. The overall sensitivity of the experimental apparatus and the minimum concentration value of the marker were then estimated.     

R.F. (280 MHz) EPR imaging of extended samples: Apparatus and preliminary results

This paper presents the preliminary results obtained using an Electron Paramagnetic Resonance imaging apparatus operating at 280 MHz. The acquisition technique and the procedure used to obtain the spin density spatial localization are presented and specimen images of extended samples are given. The accuracy of the images and the spatial resolution are also discussed.     

The effect of composition of parenteral solution on the thermal resistance of Bacillus stearothermophilus and Bacillus subtilis spores

Large-volume parenteral solutions were submitted to heat treatments after being inoculated with Bacillus stearothermophilus ATCC 7953 (T _r =121°C) and Bacillus subtilis ATCC 9372 (T _r =104.5°C) spores. The average decimal reduction time for B. stearothermophilus ranged from a D _121°C value of 1.31 to 3.14 min, in glucophysiologic and Ringer’s solutions respectively. For B. subtilis, D _104.5°C value increased from 0.69 to 1.37 min, in Ringer’s (pH=5.91) and 50% glucose (pH 3.05) solutions respectively. The z value ranged from 7.95°C (20% mannitol solution) to 13.14°C (50% glucose solution), corresponding to an activation energy (Ea) of 81.48 and 49.30 kcal/mol, respectively.     

Evaluation of recombinant green fluorescent protein, under various culture conditions and purification with HiTrap hydrophobic interaction chromatography resins

To determine the influence of various culture conditions, transformed cells of Escherichia coli expressing recombinant green fluorescent protein (GFPuv) were grown in nine cultures with four variable conditions (storage of inoculated broth at 4°C prior to incubation, agitation speed, isopropyl-β-d-thiogalactopyranoside [IPTG] concentration, and induction time). The pelleted cells were resuspended in extraction buffer and subjected to the three-phase partitioning (TPP) extraction method. To determine the most appropriate purification resin, protein extracts were eluted through one of four types of HiTrap hydrophobic interaction chromatography (HIC) columns prepacked with methyl, butyl, octyl, or phenyl resins and analyzed further on a 12% sodium dodecylsulfatepolyacrylamidegel. With Coomassie staining, a single band between 27 (standard GFPuv) and 29 kDa (molecular weight standard) was visualized for every HIC column sample. TPP extraction with HIC elution provided about 90% of the GFPuv recovered and eight-fold GFPuv enrichment related to the specific mass. Rotary speed and IPTG concentration showed, respectively, greater negative and positive influences on GFPuv expression at the beginning of the logarithmic phase for the set culture conditions (37°C, 24-h incubation).     

Permeation associated with three-phase-partitioning method on release of green fluorescent protein

Transformed cells of Escherichia coli expressing recombinant green fluorescent protein (GFPuv) were subjected to two methods of extraction: (1) freezing/thawing/sonication (FTS) cycles prior to the three-phase partitioning (TPP) method, or (2) directly to TPP extraction. The amount of GFPuv released by the FTS plus TPP method varied: 374μg/mL (first cycle), 93–442 μg/mL (second cycle), 32–359 μg/mL (third cycle), 18–115 μg/mL (fourth cycle). The GFPuv yields by the second method (TPP only) were, 23–54 μg/mL for the first extract and 33–91 μg/mL for the second. The FTS plus TPP method released similar amounts of GFPuv to that extracted by TPP; and provided a better mixture elution through the hydrophobic interaction column: 13–63 μg/mL for FTS plus TPP methods, and 2.5–13 μg/mL for TPP. The results showed that although selective permeation is a more laborious methodology, it was more efficient for obtaining of GFPuv in relation to the direct extraction of the cells for TPP.     

Designing generalized statistical ensembles for numerical simulations of biopolymers

Conformational properties of polymers, such as average dihedral angles or molecular alpha-helicity, display a rather weak dependence on the detailed arrangement of the elementary constituents (atoms). We propose a computer simulation method to explore the polymer phase space using a variant of the standard multicanonical method, in which the density of states associated to suitably chosen configurational variables is considered in place of the standard energy density of states. This configurational density of states is used in the Metropolis acceptance/rejection test when configurations are generated with the help of a hybrid Monte Carlo algorithm. The resulting configurational probability distribution is then modulated by exponential factors derived from the general principle of the maximal constrained entropy by requiring that certain average configurational quantities take preassigned (possibly temperature dependent) values. Thermal averages of other configurational quantities can be computed by using the probability distributions obtained in this way. Moments of the energy distribution require an extra canonical sampling of the system phase space at the desired temperature, in order to locally thermalize the configurational degrees of freedom. As an application of these ideas we present the study of the structural properties of two simple models: a bead-and-spring model of polyethylene with independent hindered torsions and an all-atom model of alanine and glycine oligomers with 12 amino acids in vacuum.     

Zn-Induced Interactions Between SARS-CoV-2 orf7a and BST2/Tetherin

We present in this work a first X-ray Absorption Spectroscopy study of the interactions of Zn with human BST2/tetherin and SARS-CoV-2 orf7a proteins as well as with some of their complexes. The analysis of the XANES region of the measured spectra shows that Zn binds to BST2, as well as to orf7a, thus resulting in the formation of BST2-orf7a complexes. This structural information confirms the the conjecture, recently put forward by some of the present Authors, according to which the accessory orf7a (and possibly also orf8) viral protein are capable of interfering with the BST2 antiviral activity. Our explanation for this behavior is that, when BST2 gets in contact with Zn bound to the orf7a Cys₁₅ ligand, it has the ability of displacing the metal owing to the creation of a new disulfide bridge across the two proteins. The formation of this BST2-orf7a complex destabilizes BST2 dimerization, thus impairing the antiviral activity of the latter.     

Charged tensor matter fields and Lorentz symmetry violation via spontaneous symmetry breaking

We consider a model with a charged vector field along with a Cremmer-Scherk-Kalb-Ramond (CSKR) matter field coupled to a U(1) gauge potential. We obtain a natural Lorentz symmetry violation due to the local U(1) spontaneous symmetry breaking mechanism triggered by the imaginary part of the vector matter. The choice of the unitary gauge leads to the decoupling of the gauge-KR sector from the Higgs-KR sector. The excitation spectrum is carefully analyzed and the physical modes are identified. We propose an identification of the neutral massive spin-1 Higgs-like field with the massive Z boson of the so-called mirror matter models.Received: 30 October 2003, Revised: 16 March 2004, Published online: 23 June 2004     

Recognition games

In this work we propose an evolution model based on the competition between individuals belonging to populations of neural networks, obeying the Hopfield dynamics. The selection rule adopted relies on generalization and natural classification abilities. The results obtained through computer simulation show that these populations self-organize and evolve towards equilibrium states in the region of transition between ordered and disordered phases. Received 28 October 1998 and Received in final form 2 December 1998