固氮酶铬铁蛋白的晶体生长

在合适的结晶条件下 ,从含Cr无氨培养基中生长的固氮菌 (AzotobactervinelandiiLipmann)突变种UW3 中纯化出的CrFe蛋白可从溶液中析出深棕色斜四棱柱晶体 ,晶体最大的两条对角线长度分别可达 0 .2 5mm和 0 .12mm。PEG 80 0 0、MgCl2 、NaCl、Tris和Hepes缓冲液的浓度及结晶方法等对该蛋白的出晶率、晶核数目、晶体大小和质量都有明显影响。CrFe蛋白结晶所需的上述化合物的最适浓度与在Mn中生长的固氮菌突变种UW3 的MnFe蛋白和缺失nifZ固氮菌突变种的ΔnifZMoFe蛋白结晶所需的最适浓度有所不同。结果表明 ,该蛋白晶体可能为CrFe蛋白的晶体     

含锰固氮酶组分Ⅰ蛋白的纯化和特性

棕色固氮菌（Azotobacter vinelandii Lipmann)突变种UW3能在无Mo的无氨培养基中固氮生长,低浓度的Mn对UW3突变种生长有促进作用,从在Mn中生长的UW3菌体中分离得到的部分纯固氮酶组分Ⅰ蛋白含量有Mn和Fe原子（Fe/Mo/Mn为10．41：0．19：1．00）并有OP MoFe蛋白一半的还原乙炔和质子的活性。这种蛋白的吸收光谱和圆二色谱与MoFe蛋白存在明显的差异,含Mn蛋白的亚基分子量都与MoFe蛋白的α亚基相近。初步结果表明,这种含Mn蛋白可胡是一种固氮酶组分Ⅰ蛋白。     

Freezing of dehydrated calli of spring wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) in liquid nitrogen and their morphogenetic potential

A cryopreservation method developed earlier was modified for freezing of calli derived from mature embryos of four spring wheat (Triticum aestivum L.) pure lines. The effects of particular stages of cryopreservation protocol on water content, number of calli recovering growth, and rate of morphogenesis were analyzed. Regrowth was observed in 90.5–100% of calli after dehydration and in 93.3–100% after freezing-thawing. Dehydration, but not freeze-thawing significantly decreased the frequency of morphogenetic variation.     

Descriptive Modeling of the Dynamical Systems and Determination of Feedback Homeostasis at Different Levels of Life Organization

The state-of-art research in the field of life’s organization confronts the need to investigate a number of interacting components, their properties and conditions of sustainable behaviour within a natural system. In biology, ecology and life sciences, the performance of such stable system is usually related to homeostasis, a property of the system to actively regulate its state within a certain allowable limits. In our previous work, we proposed a deterministic model for systems’ homeostasis. The model was based on dynamical system’s theory and pairwise relationships of competition, amensalism and antagonism taken from theoretical biology and ecology. However, the present paper proposes a different dimension to our previous results based on the same model. In this paper, we introduce the influence of inter-component relationships in a system, wherein the impact is characterized by direction (neutral, positive, or negative) as well as its (absolute) value, or strength. This makes the model stochastic which, in our opinion, is more consistent with real-world elements affected by various random factors. The case study includes two examples from areas of hydrobiology and medicine. The models acquired for these cases enabled us to propose a convincing explanation for corresponding phenomena identified by different types of natural systems.     

Characteristics of tumors that have developed in mice injected with syngenic irradiated mesenchymal stem cells of bone marrow

Mesenchymal stem cells (MSCs) are found in virtually all organs and tissues. These cells can presumably be transformed into tumor stem cells by genotoxic factors and, subsequently, initiate tumor growth. The aim of the present work consisted in analysis of the possibility of malignant transformation of cultured MSCs from the bone marrow (BM) of mice after in vitro exposure to γ-radiation and in the characterization of biochemical and histological features of tumors that developed after the transplantation of BM MSCs to syngenic mice. Two of five mice developed tumors 3 to 4 months after the subcutaneous injection of BM MSCs irradiated at a dose of 1 Gy, five of five animals developed tumors after the administration of BM MSCs irradiated at a dose of 6 Gy, and only one of five mice injected with nonirradiated BM MSCs developed a tumor 6 months after cell transplantation. Telomerase activity in a tumor that developed from BM MSCs irradiated at a dose of 6 Gy was twice as high as that in the tumor that developed from BM MSCs irradiated at a dose of 1 Gy. The histological structure of the neoplasms corresponded to that of multicomponent mesenchymoma, a malignant tumor also termed “a mix of sarcomas.” The tumors consisted of tissue fragments of different histological types. Thus, BM MSCs exposed to 1 or 6 Gy of radiation can be transformed into tumor cells and give rise to multicomponent mesenchymomas, whereas malignant transformation of control BM MSCs occurs much less often.     

State-dependent cAMP binding to functioning HCN channels studied by patch-clamp fluorometry

One major goal of ion channel research is to delineate the molecular events from the detection of the stimuli to the movement of channel gates. For ligand-gated channels, it is challenging to separate ligand binding from channel gating. Here we studied the cyclic adenosine monophosphate (cAMP)-dependent gating in hyperpolarization-activated cAMP-regulated (HCN) channel by simultaneously recording channel opening and ligand binding, using the patch-clamp fluorometry technique with a unique fluorescent cAMP analog that fluoresces strongly in the hydrophobic binding pocket and exerts regulatory effects on HCN channels similar to those imposed by cAMP. Corresponding to voltage-dependent channel activation, we observed a robust, close-to-threefold increase in ligand binding, which was more pronounced at subsaturating ligand concentrations than higher concentrations. This observation supported the cyclic allosteric models and indicated that protein allostery can be implemented through differentiating ligand binding affinities between resting and active states. The kinetics of ligand binding largely matched channel activation. However, during channel deactivation, ligand unbinding was slower than channel closing, suggesting a delayed response to membrane potential by the ligand binding machinery. Our results provide what we believe to be new insights into the cAMP-dependent gating in HCN channel and the interpretation of protein allostery for general ligand-gated channels and receptors.     

Regulation of cytokinin oxidase activity as a factor affecting the content of cytokinins

In the shoots of 7-day-old seedlings of wheat (Triticum durum Desf., cv. Bezenchukskaya 139), ion deficiency in Hoagland-Arnon nutrient solution induced a decrease in the cytokinin content by the end of the first day, whereas the excision of four out of five primary roots brought about an opposite response (accumulation of cytokinins) as early as during the first hour. It was assumed that changes in the content of cytokinins might depend on the activity of cytokinin oxidase (CKO) and the expression of gene encoding this enzyme. It was shown that tenfold dilution of the nutrient solution activated CKO and raised the level of CKO gene expression, whereas excision of some roots brought about a quick decrease in enzyme activity and gene expression. The role of ABA and arrival of cytokinins from the roots to the shoot as factors affecting CKO activity in the shoot is discussed; arguments for the priority of hormonal signal over the influx of nitrates from the roots are offered. It was concluded that the regulation of CKO activity might be one of the important mechanisms determining plant response to treatments via the changes in the cytokinin concentration.     

Structural Basis for the cAMP-dependent Gating in the Human HCN4 Channel

Hyperpolarization-activated cAMP-regulated (HCN) channels play important physiological roles in both cardiovascular and central nervous systems. Among the four HCN isoforms, HCN2 and HCN4 show high expression levels in the human heart, with HCN4 being the major cardiac isoform. The previously published crystal structure of the mouse HCN2 (mHCN2) C-terminal fragment, including the C-linker and the cyclic-nucleotide binding domain (CNBD), has provided many insights into cAMP-dependent gating in HCN channels. However, structures of other mammalian HCN channel isoforms have been lacking. Here we used a combination of approaches including structural biology, biochemistry, and electrophysiology to study cAMP-dependent gating in HCN4 channel. First we solved the crystal structure of the C-terminal fragment of human HCN4 (hHCN4) channel at 2.4 Å. Overall we observed a high similarity between mHCN2 and hHCN4 crystal structures. Functional comparison between two isoforms revealed that compared with mHCN2, the hHCN4 protein exhibited marked different contributions to channel function, such as a ∼3-fold reduction in the response to cAMP. Guided by structural differences in the loop region between β4 and β5 strands, we identified residues that could partially account for the differences in response to cAMP between mHCN2 and hHCN4 proteins. Moreover, upon cAMP binding, the hHCN4 C-terminal protein exerts a much prolonged effect in channel deactivation that could have significant physiological contributions.     

Effect of partial root excision on shoot water relations

Removing 4 out of 5 serminal roots from 7-day-old wheat seedlings arrested leaf elongation for 1.5 h. This effect can be explained by an initial decrease in foliar water content resulting from the smaller root surface area available for water uptake. Subsequently, leaf hydration increased with time and came to equal that of intact plants within 2 h. The rehydration was seemingly effected by an increasing conductivity of the one remaining root axis, since transpiration of the partially de-rooted plants did not fall below that of controls. With time, leaf elongation resumed, but at a slower rate than in intact plants. This slower growth may be attributed to a decrease in leaf extensibility since this was found to be reduced when measured by a counterweight technique involving linear displacement transducers. Loss of extensibility was associated with decreased IAA concentration in the leaf elongation zone.