Biophysics最新文献

The process of amyloid aggregation is quite complex and poorly studied. In this paper, summarizing the previously obtained results on the aggregation of the multidomain smooth muscle protein titin, we tried to complement the idea of its amyloid aggregation by presenting a new, in our opinion, possible mechanism. The main conclusion is that the ability of titin to form amorphous aggregates seems to be the only possible means of aggregation of this protein. Apparently, only individual sections of the molecules, and not the entire protein, are involved in the formation of the amyloid structure in amorphous aggregates of smooth muscle titin. This feature distinguishes titin from other amyloid or amyloid-like proteins due to the large size of the molecule. The possible energy landscape underlying the formation of amyloid aggregates of titin is discussed.

A mathematical study of fluorescence spectrum related to photosynthesis action spectrum was carried out, the calculation of typical photosynthesis spectra on the frequency scale for red and blue light was performed, and the transition of the photosynthesis action spectrum from wavelengths to the frequency scale was carried out; as a result of the inverse Fourier transform, a relaxation curve of the pulse (time) characteristic of fluorescence was numerically obtained. It turned out that the radius vector of the pulse response modulus in polar coordinates made one half turn or half the period of light oscillations in time. It has been found that the optical medium of a plant has a negative volume charge of electrons during relaxation and has inverse properties and properties of coherent radiation. The condition of neutrality of the material environment is not fulfilled. It was revealed that the ratios of variable chlorophyll fluorescence for red and blue light have almost the same value. An analysis of the dependence of the quality factor of the chlorophyll spectrum on frequency showed that the loss of fluorescence energy in blue light significantly exceeds the loss of energy in red light. The proposed method can be used for rapid analysis of photosynthesis intensity. It is also concluded that plants can emit ultra-wideband signals. The relaxation time of chlorophyll fluorescence is shorter than the relaxation time of electron polarization in atoms (molecules). As a result, an inversion of populations is created in the optical medium of chlorophyll, that is, there are more atoms at the upper energy level than at the lower one. Due to this, forced emission and amplification of the light of radiative recombination occurs. In this case, the emission of fluorescence light becomes coherent. All these properties of plants were considered for the first time and were not described in either the domestic or foreign literature.

Simultaneous observations of radioactivity fluctuations from the natural isotope ⁴⁰K were carried out in Moscow and Ulyanovsk. It was found that the changes in the counting rate from sources in these geographical points were not simultaneous, but were synchronized according to local solar time. Based on this observation and considering that radioactivity fluctuations correlated with body temperature rhythms, a method for short-term prediction of ultradian rhythms of animal activity has been developed and confirmed. An analysis of the consistency of the dynamics of the intensity of decay fluctuations and daily growth rates of an L-929 cell culture was also carried out. It was found that the highest correlation coefficient was recorded when the indicator of proliferative activity of the culture was compared with the intensity of decay fluctuations taken over the previous day. Thus, based on data on fluctuations in the radioactive decay of ⁴⁰K, which are an indicator of the biotropic factor of the environment, it is possible to make short-term forecasts of ultradian and infradian biological rhythms.

This study examined radiosensitivity to low- and high-dose exposure to X-rays in human lymphocytes and the ability of low and high radiation doses to induce radioadaptive response when peripheral blood cells from patients with secondary immune deficiency syndrome and healthy donors of different ages were irradiated in vitro. The occurrence of micronuclei in cytochalasin-blocked binucleated lymphocytes in culture served as an indication of cytogenetic damage. It was found that the spontaneous level of cytogenetic damage in blood lymphocytes of patients with secondary immune deficiency syndrome was 2.5 times greater than in healthy young and older volunteers, and there was also a substantial interindividual variability in the outcome parameters as compared to the data of control groups. There were no differences in the mean values for radiosensitivity to low- and high-dose exposure to X-rays between the groups. In all groups, no correlation was shown between the spontaneous level of micronuclei in lymphocytes and the radiosensitivity of individuals. The adaptive response was induced with the same frequency and to the same extent in lymphocytes in patients with secondary immune deficiency syndrome and in healthy donors of different ages.

The combined use of X-ray irradiation and photodynamic therapy on a model of human lung adenocarcinoma A549 cells has been investigated. It was found that synchronous exposure to two types of radiation contributed to a stronger decrease in the survival rate of tumor cells than their sequential use or each type of radiation separately. The levels of RNA and expression of a number of genes involved in cell cycle control (p21 and DINOL), apoptosis (BAX and PUMA) and DNA repair (PARP1, OGG1, Rad51, and Lig4) were determined for various combinations of these two types of irradiations of cells. The highest level of expression under all treatments was observed for the long noncoding RNA of DINOL gene. The detected increase in the expression of the BAX and PUMA genes indicated the development of apoptosis. The results we obtained confirmed the synergism of radiation and photodynamic therapy upon their simultaneous use.

The temporal resolving power of the visual system is essential for the perception of the objective world. The lowest sampling rate of a sequence of images at which perception becomes fused is called the critical flicker fusion frequency (CFFF). A variety of experimental data on critical frequency thresholds can be explained from the viewpoint of a model of the contrast sensitivity of the visual system that is based on the tremor modulation signal (TMS). The model describes how the critical frequency depends on the stimulus brightness, adaptation brightness, and the duration and angular size of the stimulus. The model demonstrates that critical frequency values lie in a range up to 1000 Hz for bright stimuli of a short duration and a large angular size, that a frame rate of 300–500 Hz should be considered optimal for the visual system, and that the critical frequency lies in a low-frequency region for small-sized angular stimuli. Differences in the rate of flicker fusion can be explained by temporal sensitivity of magnocellular and parvocellular neurons.

It is shown that there is no need to resort to exoteric hypotheses to explain flight in a dream. From the standpoint of biophysics, the phenomenon of “flying in a dream” is based on the already studied adaptive mechanisms and circadian rhythms of the human body. During sleep, the brain’s excitation thresholds change; this makes it easier in some brain areas to excite weak signals. One of the mechanisms of such excitation occurs when a person changes his posture during sleep, which is perceived by the brain in the rapid eye movement sleep phase as a decrease in body weight. This, under certain conditions, can contribute to the appearance in the brain of the illusion of flight.

The nonhistone chromosomal protein HMGB1 and histone H1 are chromatin linker proteins. The functions of linker proteins are closely related to their conformational state. The structure of proteins that play a key role in the formation of higher levels of chromatin structural organization is being actively studied. In this study, a comparative analysis of the secondary structure of the linker histone H1 and the nonhistone protein HMGB1 was carried out. Using circular dichroism in the UV region and FTIR spectroscopy, it was shown that positively charged histone H1 binds to the C-terminal fragment of HMGB1, stabilizing the resulting complex and inducing the formation of additional α-helical regions in both proteins.

This study provides a review of experimental research on selection in mice, which yielded positive results. The selection of mice was high (the task required mice to understand that an object that has become invisible still exists and can be found) and poor performance occurred in a cognitive test. The results we obtained revealed better short term memory in mice selected for high performance scores and that these mice also had higher performance in tests for novelty and attention. This suggests that differences between the mice used in the experiment are associated not only with cognitive abilities in tests, but also with more pronounced “executive functions.”

The effects of the β-adrenergic receptor agonist isoproterenol on the contractile activity of the papillary muscle of the rat heart right ventricle were studied both at a temperature close to physiological (30°C) and under conditions of deep hypothermia (10°C). Isoproterenol had a pronounced positive inotropic effect at 30°C, the contraction force increased from 1.2 ± 0.1 mN in the control to 2.4 ± 0.4 mN after the addition of the agonist and there was a significant acceleration of the time parameters of contraction, that is, the time to reach the maximum contraction decreased from 101 ± 6 ms to 85 ± 4 ms; the relaxation time decreased by 50% from 55 ± 3 ms to 36 ± 1 ms. Under hypothermic conditions, isoproterenol caused a powerful negative inotropic effect, reducing the contraction force from 2.2 ± 0.4 mN to 1.2 ± 0.4 mN. The tendency to accelerate contraction persisted as at 30°C: the time to reach the maximum contraction decreased from 717 ± 52 ms to 624 ± 50 ms, and the relaxation time decreased by 50% from 667 ± 86 ms to 450 ± 40 ms. Thus, under conditions of deep hypothermia at 10°C, the direction of the inotropic response to isoproterenol changed from positive to negative, while the lusitropic effect remained negative.