The discovery of a subunit exchange in some oligomeric proteins, implying short-term dissociation of their oligomeric structure, requires new insights into the role of the quaternary structure in oligomeric protein stability and function. Here we demonstrate the effect of pH, protein concentration, and urea on the efficiency of GroES heptamer (GroES7) subunit exchange. A mixture of equimolar amounts of wild-type (WT) GroES7 and its Ala97Cys mutant modified with iodoacetic acid (97-carboxymethyl cysteine or CMC-GroES7) was incubated in various conditions and subjected to isoelectric focusing (IEF) in polyacrylamide gel. For each sample, there are eight Coomassie-stained electrophoretic bands showing different charges that result from a different number of included mutant subunits, each carrying an additional negative charge. The intensities of these bands serve to analyze the protein subunit exchange. The protein stability is evaluated using the transverse urea gradient gel electrophoresis (TUGGE). At pH 8.0, the intensities of the initial bands corresponding to WT-GroES7 and CMC-GroES7 are decreased with a half-time of (23 ± 2) min. The exchange decreases with decreasing pH and seems to be strongly hindered at pH 5.2 due to the protonation of groups with pK ∼ 6.3, which stabilizes the protein quaternary structure. The destabilization of the protein quaternary structure caused by increased pH, decreased protein concentration, or urea accelerates the GroES subunit exchange. This study allows visualizing the subunit exchange in oligomeric proteins and confirms its direct connection with the stability of the protein quaternary structure.

An avalanche silicon photodiode has been developed for the near IR, visible, UV and VUV light ranges. The external quantum efficiency has been studied in the 114–170 and 210–1100 nm ranges. It has been demonstrated that the avalanche photodiode reaches the quantum yield of 29 to 9300 electrons/photon at the 160 nm wavelength and bias voltage of 190–303 V, respectively.

Avalanche silicon photodiode have been developted for near ir, visible, UV and VUV light range. External quantum efficiency have been studied in 114 - 170 abd 210 - 1100nm range. It is demonstrated that photodiode reach from 29 to 9300 electrons/photon on 160 nm with bias voltage of 190 and 303 v respectively.

The production of recombinant proteins in Escherichia coli cells is often hampered by aggregation of newly synthesized proteins and formation of inclusion bodies. Here we propose the use of transverse urea gradient electrophoresis (TUGE) in testing the capability of folding of a recombinant protein from inclusion bodies dissolved in urea. A plasmid encoding the amino acid sequence 55–224 of TcpA pilin (C-terminal globular domain: TcpA-C) from Vibrio cholerae El Tor enlarged by a His-tag on its N-terminus was expressed in E. coli cells. The major fraction (about 90%) of the target polypeptide was detected in cell debris. The polypeptide was isolated from the soluble fraction and recovered from inclusion bodies after their urea treatment. Some structural properties of the polypeptide from each sample proved identical. The refolding protocol was developed on the basis of TUGE data and successfully used for the protein large-scale recovery from inclusion bodies. Spectral, hydrodynamic, and thermodynamic characteristics of the recombinant TcpA recovered from inclusion bodies indicate the presence of a globular conformation with a pronounced secondary structure and a rigid tertiary structure, which is promising for the design of immunodiagnostics preparations aimed to assess the pilin level in different strains of V. cholerae and to develop cholera vaccines.

Although oligomeric proteins are predominant in cells, their folding is poorly studied at present. This work is focused on the denaturant- and mutation-induced disassembly of the hexameric mutant Y55W of the Qβ host factor (Hfq) from mesophilic Pseudomonas aeruginosa (Pae). Using intrinsic tryptophan fluorescence, dynamic light scattering (DLS), and high-performance liquid chromatography (HPLC), we show that the dissociation of Hfq Y55W occurs either under the effect of GuHCl or during the pre-denaturing transition, when the protein concentration is decreased, with both events proceeding through the accumulation of stable intermediate states. With an extremely low pH of 1.4, a low ionic strength, and decreasing protein concentration, the accumulated trimers and dimers turn into monomers. Also, we report on the structural features of monomeric Hfq resulting from a triple mutation (D9A/V43R/Y55W) within the inter-subunit surface of the protein. This globular and rigidly packed monomer displays a high thermostability and an oligomer-like content of the secondary structure, although its urea resistance is much lower.

The external quantum yield of silicon avalanche photodiode in the wavelength range of 120-170 nm was performed. It was shown that the engineered avalanche photodiode has the external quantum yield of 24-150 electron/proton under reverse bias voltage of 230-345 V, respectively. The testing of worked out avalanche photodiode by means of pulse flash of 280 and 340 nm wavelength demonstrates the speed, corresponding to the bandwidth not less than 25 MHz.

We have designed a silicon avalanche photodiode for detecting vacuum ultraviolet radiation. The external quantum yield of a silicon avalanche photodiode has been investigated in the wavelength range of 120–170 nm. It is shown that the avalanche photodiode has an external quantum yield of 24–150 electrons/photons at a reverse bias voltage of 230–345 V. Testing of this avalanche photodiode with pulsed illumination at wavelengths of 280 and 340 nm has shown performance corresponding to a transmission band no narrower than 25 MHz.

Quantum photoresponse yield of a silicon XUV avalanche photodiode prototype with 1.5‑mm-diameter active region has been studied in the 320–1100 nm wavelength range. It is established that the proposed avalanche photodiode has the external quantum efficiency above 20 electron/photon in the 580–1000 nm range at a reverse bias voltage of 485 V.

The sensitivity at wavelengths in the range 400–1150 nm, dark current, and dynamic characteristics of an silicon avalanche photodiode with an active region 1.5 mm in diameter that we developed have been examined. It has been shown that the avalanche photodiode has the following set of characteristics: sensitivity 80–85 A/W at wavelengths of 900–1010 nm, dark current 1.5 nA, and leading and trailing edges shorter than 2.5 ns at a reverse bias voltage of 350 V.

Silicon XUV avalanche photodiode prototype quantum yield have been explored with an active area of 1.5 mm in a 320 – 1100 nm spectral range. Quantum yield of a 20 electron per photon have been reached in 580 – 1000 nm spectral range with bias 485 V.

Sensitivity in 400 – 1150 nm spectral range, dark current and dynamic characteristics have been tested of a developed silicon avalanche photodiode with an active diameter of 1.5 mm. Developed Si APD possesses: photosensitivity 80-85 A/W in 900 - 1010 nm spectral range, 1.5 nA dark current, rise and fall time less than 2.5 ns with a bias voltage of 350 v.

A microfluidic system of capillary electrophoresis with electrochemical detection is developed. The process of manufacturing a chip based on polydimethylsiloxane and glass for the determination of electroactive compounds is described. We studied the possibilities of the treatment of the chip channel surface in a gas discharge with sodium dodecyl sulfate, sodium deoxycholate, and an ionic liquid of 1-dodecyl-3-trimethylimidazolium chloride, used as additives to the background electrolyte. It was found that the developed microfluidic system can be used for the determination of polyphenolic antioxidants in green tea and red wine.

Hfq is a thermostable RNA-binding bacterial protein that forms a uniquely shaped homohexamer. Based on sequence and structural similarity, Hfq belongs to the like-Sm (LSm) protein family. In spite of a rather high degree of homology between archaeal and eukaryotic LSm proteins, their quaternary structure is different, usually consisting of five to eight monomers. In this work, the importance of conserved intersubunit hydrogen bonds for the Hfq spatial organization was tested. The structures and stabilities for the Gln8Ala, Asn28Ala, Asp40Ala, and Tyr55Ala Hfq mutants were determined. All these proteins have the same hexamer organization, but their stability is different. Elimination of a single intersubunit hydrogen bond due to Gln8Ala, Asp40Ala, and Tyr55Ala substitutions results in decreased stability of the Hfq hexamer. Tyr55Ala Hfq as well as the earlier studied His57Ala Hfq has reduced protein thermostability, which seems to correspond to an opening of the protein hydrophobic core.

Photoresponse of a silicon multipixel photon counter (MPPC) operating in the Geiger breakdown regime has been studied at wavelengths λ = 115, 121, 128, 160, and 175 nm. It is established that radiation intensity at these wavelengths can be measured by MPPC at room temperature in the photon-count mode with efficiency on a level of 2%.

Описано изготовление чип-анализатора на основе полидиметилсилоксана и стекла. Изучены возможности обработки поверхности канала чипа атмосферной плазмой и додецилсульфатом натрия, используемым в качестве добавки к рабочему буферу. Оценена скорость электроосмотического потока. На модельной смеси катехоламинов выявлено влияние модификации поверхности каналов микрочипа на эффективность и факторы разрешения. Найдены способы повышения чувствительности электрохимической ячейки; выявлены возможности on-line концентрирования в чип-формате. Достигнут предел детектирования катехоламинов 10-6 10-7 г/мл.

The extremely low level of intrinsic noise attained in silicon detectors with “ideal-diode” current-voltage characteristics has made it possible to create measuring circuits capable of detecting currents as low as 10 −16 A and, at the same time, featuring a dynamic range as large as 10 11 –10 12 .

The spatial homogeneity of the photoresponse is studied for silicon photodiodes based on p-n and n-p junctions a year after their irradiation at a wavelength of 121.6 nm and those based on n-p junctions four years after their irradiation with soft X-rays. It is demonstrated that silicon photodiodes based on p-n junctions exhibit a photoresponse recovery effect on being irradiated at a wavelength of 121.6 nm. No recovery effect is observed for silicon photodiodes based on n-p structures.