Coupling between transmembrane calcium transport and membrane potential in retinal rod discs

Changes in the transmembrane potential of bovine rod discs were studied by use of the potential-sensitive fluorescence probes diS-C3-(5) and diBA-C4-(5). The disc membrane was shown to be impermeable to potassium ions. Their concentration in the disc is as high as 2.1 +/- 0.3 mM. The permeability of the disc membrane to Ca2+ was shown to be selective. The accumulation and release of Ca2+ were found to be accompanied by the generation of inside positive and inside negative transmembrane potentials, respectively. The uptake of Ca2+ in the discs may operate against the concentration gradient of the ion. The value of the potential developed is directly proportional to the logarithm of free Ca2+ concentration in the medium (delta phi m = 11.2 +/- 1.6 mV at 4.85 microM Ca2+fr). The accumulation of Ca2+ is decreased by sodium ions and totally inhibited by monensin. This indicates that a Na-Ca exchange process participates in Ca2+ uptake of photoreceptor discs.     

Polydimethylsiloxane Films Modified with Chitosan/Pectin Multilayers as Scaffolds for Mesenchymal Stem Cells

Solid (smooth) and porous films of polydimethylsiloxane (PDMS) have been obtained; the effect of their structure on the adhesion of mesenchymal stem cells (MSCs) on their surface was found. It is shown that modification of these films with a (chitosan/pectin)₄ multilayer increased the efficiency of viable cell adhesion. A (3-aminopropyl)triethoxysilane–glutaraldehyde system was used to enhance the binding of the polysaccharide layer to the hydrophobic surface of PDMS. It was found that MSCs formed a monolayer culture of the fibroblast-like cells with high viability on porous PDMS modified with (chitosan/pectin)₄.     

cGMP-binding centers in photoreceptor membranes

The binding of cGMP by structural components of bovine rod outer segments was studied. The discs and plasma membranes were shown to contain two types of the specific binding sites for cGMP which are distinct from cyclic GMP phosphodiesterase. The sites have a "high" and "low" (Kd = 0.1 divided by 0.35 and 1.5 divided by 2.0 X 10(-6) M respectively) affinity for cGMP. They belong to membraneous integral proteins presumably associated with phospholipids. Their affinity for cGMP is controlled by GTP and calmodulin.     

Magnetic interaction of manganese with pheophytin anion-radical and chlorophyll cation-radical in reaction centers of the photosystem II

The influence of Mn on saturation curves of ESR spectra of Ph(-) and P(+)(680) at 1-200K in samples with different content of Mn has been studied. An analysis of these data and those on photoinduced changes of fluorescence yield of chlorophyll leads to the conclusion that the Mn-containing centre in Photosystem 2 is a cluster of 4 Mn atoms, two of which can be replaced by Mg(2+) or any other divalent metal. The distances between Mn Na Ph as well as between Mn and P(680) have been estimated.     

Influence of UV-light on erythrocyte membrane structure and catalytic behaviour of membrane acetylcholine esterase]

UV-light is shown to induce the structural transitions in the erythrocyte membrane described by S-shape curves in plots of the structural response versus the irradiation dose. In contrast to the free acetylcholine esterase (AChE) UV-light acts on the membrane enzyme as a mixed inhibitor (simultaneous change in Vmax and Km). The modification of the environment structure of residual enzyme is suggested to be the main reason of this phenomenon. The effect is under the control of membrane integrity and disappears after its desintegration. Membrane AChE treated ultrasonically both prior to and after irradiation is inactivated without a Km change. The data obtained show the influence of erythrocyte membrane structure on the catalytic behaviour of membrane-bound AChE.     

Preparation of androsta-1,4-diene-3,17-dione from sterols using Mycobacterium neoaurum VKPM As-1656 strain

A product of microbiological cleavage of the sterols side chain, androsta-1,4-diene-3,17-dione, is toxic for bacteria, in particular, actinobacteria of the genera Mycobacterium and Arthrobacter. Sterols were transformed into androsta-1,4-diene-3,17-dione by culturing the M. neoaurum VKPM An-1656 strain in a high yield, provided that a sorbent was used for elimination of contact between the bacterial cells and the product. Unlike the cholesterol side chain, the more branched chains of phytosterols were cleaved in the presence of M. neoaurum at a high rate only under turbulent stirring of the culture medium, which intensified the formation of hydrocarbonate ion from NaNI3 in situ.     

Repolarization of canine ventricular myocardium under the supraventricular rhythm

The ventricular myocardium is characterized by heterogeneity of activation-recovery interval durations. The transmural ARI gradients are present in the right ventricular apex (ARIs monotonically decreased as one moved from the endocardium to the epicardium), and in the left ventricular base (repolarization in the subepicardial layers was significantly shorter than that in the midmyo cardial layers whereas subendocardial ARIs did not differ from the others). The repolarization pattern of these myocardial regions is governed by the distribution of ARIs. In the apical left ventricular and basal right ventricular areas, no significant transmural differences in the repolarization durations were found. The repolarization pattern of these myocardial regions is governed by the activation sequence. In the right ventricle, ARIs were significantly longer at the base and shorter at the apex. In contrast, in the left ventricle, the apical ARIs were prolonged whereas the basal ARIs were abbreviated. The apex-to-base sequence of myocardial repolarization seems to depend on apex-to-base gradient of activation-recovery intervals durations.     

Protein splicing

Inteins are internal polypeptide sequences that are posttranslationally excised from a protein precursor by a self-catalyzed protein-splicing reaction. Most of inteins consist of N- and C-terminal protein splicing domain and central endonuclease domain. The endonuclease domain can initiate mobility of the intein gene, this process being named intein homing. This review is focused on the recent data about the structure and function of inteins. Main intein-mediated protein-engineering applications, such as protein purification, ligation and cyclization, new forms of biosensors, are presented.