Cell-Free Synthesis of Selenoproteins in High Yield and Purity for Selective Protein Tagging

The selenol group of selenocysteine is much more nucleophilic than the thiol group of cysteine. Selenocysteine residues in proteins thus offer reactive points for rapid post-translational modification. Herein, we show that selenoproteins can be expressed in high yield and purity by cell-free protein synthesis by global substitution of cysteine by selenocysteine. Complete alkylation of solvent-exposed selenocysteine residues was achieved in 10 minutes with 4-chloromethylene dipicolinic acid (4Cl-MDPA) under conditions that left cysteine residues unchanged even after overnight incubation. Gd^III−Gd^III distances measured by double electron–electron resonance (DEER) experiments of maltose binding protein (MBP) containing two selenocysteine residues tagged with 4Cl-MDPA-Gd^III were indistinguishable from Gd^III−Gd^III distances measured of MBP containing cysteine reacted with 4Br-MDPA tags.     

Dead-beat Control of Third-order Servo-systems†

In this paper a method of obtaining dead-beat response of third-order servo systems is described. It is shown that among the three state variables of the system, e.g. error, output velocity and output acceleration, the first two, following a step signal input, attain zero values simultaneously—for an instant for certain combinations in the system parameters. For such an initial adjustment of the parameters, the system response can be made dead-beat if the parameters are suitably controlled in a discrete manner from an instant of very small value of the error. A switching circuit is described for achieving the discrete control. Results of studies of a proposed third system simulated on the analogue computer are also given.     

On the Stability of a Hysteretic System under Sinusoidal Excitation†

Expressions for the Dual Input Describing Functions (DIDF's) of a two-state relay with hysteresis have been obtained by using an equivalent function generator for the non-linearity. These DIDF's were then applied to analyse the effects of sinusoidal input signals on the stability of a feedback system which includes the hysteretic relay. These results, as substantiated by simulator data, indicate that, besides the stabilizing effects, the presence of sinusoidal signals at the input of the particular system studied may produce dual mode operation over a. range of input amplitudes.     

Gyres off the Somali coast and western boundary currents in the Bay of Bengal during the south-west monsoon

Satellite remotely-sensed sea surface temperature (SST) data were obtained during the initial phase of the onset of the south-west monsoon in the north-western Indian Ocean for the years 1987and 1988. Large wedge-like areas of upwelled water during 1988 were observed at 5°Nand 10°N after the Somali current spinup, indicative of a two-gyre circulation in the Somali current system. Satellite infrared observations of the Bay of Bengal during the early February 1990revealed the existenceof two bands of warm water that resembled a western boundary current (WBC) along the east coast of India. A warm core eddy, with a major axis of nearly 120km, appeared at 89°E and 19°N at the end of the axis of the current. The existence of the two gyre system ofT the Somali coast and the presence or absence of the WBC in the Bay of Bengal in response to the onset of the summer monsoon has been discussed in detail.     

Posicast and negicast control systems†

A possibility of obtaining dead beat response of a class of high-order control systems by adopting the technique of a single step control of the input step command is described in this paper. For achieving the desired response by such input processing techniques, the possibility demands that configurations of high-order systems be of suitable forms and the method of control necessitates positive casting of the system input like the posicast control technique in ease of oven-order systems and negative casting of the input in case of odd–order systems. The system configurations and the forms of the processed input signals in those cases have separately been investigated. The speed of the response avoiding saturated operation of such compensated systems has been studied. The effect of an improper switching operation in casting the system input has also been investigated. The results of the above studios made on the simulated systems have been given.     

Stability and controllability

The paper unifies proofs of several results on the stability of linear control systems. The proofs are based on a criterion of controllability derived in the paper. This criterion suggests an efficient test of controllability.     

Delayed self-regulation and time-dependent chemical drive leads to novel states in epigenetic landscapes

The epigenetic pathway of a cell as it differentiates from a stem cell state to a mature lineage-committed one has been historically understood in terms of Waddington''s landscape, consisting of hills and valleys. The smooth top and valley-strewn bottom of the hill represent their undifferentiated and differentiated states, respectively. Although mathematical ideas rooted in nonlinear dynamics and bifurcation theory have been used to quantify this picture, the importance of time delays arising from multistep chemical reactions or cellular shape transformations have been ignored so far. We argue that this feature is crucial in understanding cell differentiation and explore the role of time delay in a model of a single-gene regulatory circuit. We show that the interplay of time-dependent drive and delay introduces a new regime where the system shows sustained oscillations between the two admissible steady states. We interpret these results in the light of recent perplexing experiments on inducing the pluripotent state in mouse somatic cells. We also comment on how such an oscillatory state can provide a framework for understanding more general feedback circuits in cell development.     

Preparation and characterization of polyelectrolyte complex of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-trimethyl chitosan/gellan gum: evaluation for controlled release of ketoprofen

N,N,N-Trimethyl chitosan, a highly water soluble derivative of chitosan, has been made by reductive methylation of chitosan by a three-step process reported in literature. A novel polyelectrolyte complex of this derivative with gellan gum has been made by mixing the aqueous solutions of the two polymers. The complex was characterized by FTIR, TGA, DSC and SEM techniques. Maximum yield of the complex was obtained at pH 2.0 with a gellan gum:trimethylchitosan ratio of 3:1. The swelling study indicated pH responsiveness of the polyelectrolyte complex sample, with higher swelling under neutral or slightly basic conditions. In vitro studies on the release of the drug ketoprofen from the polyelectrolyte complex matrix were conducted in simulated gastric and intestinal fluids. The results indicated release of 85–90 % of the entrapped drug in the media of pH 6.8 and 7.4 and less than 7 % release in the medium of pH 1.2. The kinetic analysis indicated the drug release to be a first-order process. The mechanism of water transport and drug diffusion is shown to be of Fickian type. The results prove the suitability of the polyelectrolyte complex as a matrix material for delivery of drugs with short half life such as ketoprofen in the slow release mode.     

Synthesis of Vanadate and Arsenate Spodiosites and Interpretation of Optical Spectra of Manganese-Doped Sr2VO4C1

New vanadate and arsenate analogs of spodiosite (Sr₂-(VO₄)C1 and Sr₂(AsO₄)C1) were prepared. Isomorphism between chromium and vanadium spodiosites was established by formation of complete solid solutions. The vanadate analogs of calcium and barium, the arsenate analog of calcium, phosphate analogs of strontium and barium, and the fluorine analogs, Ca₃(VO₄)₂·CaF₂ and Sr₃(VO₄)₂·SrF₂, could not be synthesized. The optical absorption spectra of manganese-doped Sr₂(VO₄)Cl showed the presence of Mn⁵⁺ in the vanadium position, the site symmetry being approximately _Td. Three transitions, ³T₂( F ), ³T₁( F ), and ¹A_l( G ) at (12,000 and 13,000 cm^-1), (16,700 cm^-1), and (14,300 cm^-1), respectively, were observed from the ground state, ³A₂( F ). The lower symmetry components were strong enough to split the energy level, ³T₂( F ). The crystal field parameter Dq and the Racah parameters B and C were calculated to be 1200, 470, and 1927 cm^-1, respectively.     

Effect of Alumina Reactivity on the Densification and Properties of Al2O3–Cr2O3 Refractories

Alumina‐chrome (Al₂O₃–Cr₂O₃) refractories with Al₂O₃:Cr₂O₃ molar ratio 1:1 were synthesized in the temperature range of 1400–1700°C by conventional solid–oxide reaction route. The effect of different aluminas (viz., hydrated and calcined) on the densification, microstructure, and properties of Al₂O₃–Cr₂O₃ refractories was investigated without changing the Cr₂O₃ source. The starting materials were analyzed to determine the chemical composition, mineralogy, density, surface area, and particle size. Sintered materials were characterized in terms of densification, phase assemblage, and mechanical strength at room temperature and at higher temperatures. Microstructural evolution at different sintering temperature was correlated with sintering characteristics. It can be concluded that the Al₂O₃–Cr₂O₃ refractories prepared with hydrated alumina as Al₂O₃ source show better densification and hot mechanical strength than corresponding calcined variety.