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Aquaporin-based biomimetic polymeric membranes
Claus Hélix-Nielsen, Joachim Habel, Michael R. Hansen, Søren Kynde, Nanna Larsen, Søren Roi Midtgaard, Grethe Vestergaard Jensen, Julie Bomholt, Anayo Ogbonna, Kristoffer Almdal, Alexander Schulz, 2015, pregledni znanstveni članek

Opis: In recent years, aquaporin biomimetic membranes (ABMs) for water separation have gained considerable interest. Although the first ABMs are commercially available, there are still many challenges associated with further ABM development. Here, we discuss the interplay of the main components of ABMs: aquaporin proteins (AQPs), block copolymers for AQP reconstitution, and polymer-based supporting structures. First, we briefly cover challenges and review recent developments in understanding the interplay between AQP and block copolymers. Second, we review some experimental characterization methods for investigating AQP incorporation including freeze-fracture transmission electron microscopy, fluorescence correlation spectroscopy, stopped-flow light scattering, and small-angle X-ray scattering. Third, we focus on recent efforts in embedding reconstituted AQPs in membrane designs that are based on conventional thin film interfacial polymerization techniques. Finally, we describe some new developments in interfacial polymerization using polyhedral oligomeric silsesquioxane cages for increasing the physical and chemical durability of thin film composite membranes.
Ključne besede: aquaporins, biomimetic membranes, block copolymers, proteopolymersomes, polyhedral oligomeric silsesquioxanes, polyamide layer, microfluidics, membrane proteins, protein-polymer-interactions
Objavljeno: 21.06.2017; Ogledov: 44; Prenosov: 0
.pdf Polno besedilo (10,59 MB)

On the role of anisotropy of membrane constituents on the elastic properties of highly curved lipid membranes
Šarka Perutkova, 2017, doktorska disertacija

Opis: The primary objective of the thesis covers in the theoretical study the role of anisotropic membrane components in the elasticity of highly curved biological membranes. To show the importance of anisotropy, we focused on one type of non-lamellar membrane self-assembly - the inverted hexagonal phase and the membrane tubular protrusions with attached proteins. These two structures represent excellent examples of highly curved structures in which the anisotropy of molecules or small domains plays an important role. In the first part of the thesis, we developed a theoretical model describing the stability of the inverted hexagonal phase, which considers lipid anisotropy and deviations from the circularity of the pivotal plane cross-section. We applied a wedge-like model of phospholipid molecules, in which the phospholipid molecule is described as a wedge, with the angle of the wedge increasing with temperature. However, we also took into account the average orientation of lipids by including the deviatoric bending energy contribution derived from statistical physics. Theoretical predictions of our model showed that a crosssection of the inverted hexagonal phase is an intermediate between a circle and a hexagon, and that it has lower energy than the circular cross-section. The results were in agreement with observations gathered by the small angle X-ray scattering. By comparing our results with the experiments, we predicted some values of the mean intrinsic curvature and the phospholipid chain stiffness. In the second part of the thesis, we developed a theoretical model, which describes the stabilisation of membrane nanotubes containing attached anisotropic flexible rod-like proteins. We derived the free energy of a vesicle with nanotube taking into account the rotational averaging of the anisotropic attached proteins. We also added the entropy contribution due to the non-homogeneous lateral distribution of proteins. Our theoretical results showed that rod-like attached proteins and membrane domains can stabilise the membrane tubular protrusions if we consider the protein/ domain anisotropy. Our results were also in agreement with experimental results in which isotropic membrane constituents were found on the tips of the nanotube or on the mother vesicle; however, the anisotropic membrane constituents were detected along the nanotubes. Our results showed that rod-like attached proteins and membrane domains can stabilise the membrane tubular protrusions if we consider the protein/domain anisotropy. The anisotropy of membrane constituents can lower the membrane free energy in regions of high curvature. The main aim of the thesis was to show that the anisotropy of membrane constituents can lower the membrane free energy in regions of high curvature and that the rotational averaging of anisotropic membrane components should be considered in the evaluation of the membrane free energy at highly curved membrane structures.
Ključne besede: Biomembranes, Lipid anisotropy, Inverted hexagonal phase, Rotational averaging, Rod-like proteins, Membrane nanotubes, Membrane protein sorting
Objavljeno: 25.05.2017; Ogledov: 91; Prenosov: 2
.pdf Polno besedilo (12,09 MB)

Effect of concentrate exchange on dairy farm
Marjan Janžekovič, Milan Repič, 2009, izvirni znanstveni članek

Opis: The purpose of the research was to establish the effect of concentrates A (C-A) and B (C-B) on the quantity and composition of the produced milk of dairy cows. The research included cows of Holstein Friesian and Simmental breeds and crossbreeds with Simmental breed. The test took place in two periods. The first period with the C-A lasted from December 2004 to February 2005 and included 113 cows. During the second period the C-B was fed. The test endured from April to June 2005. The results of monthly controls of milk quantity and protein and fat contents were entered into the Excel programme and processed with the statistical programme SPSS for Windows 12.0. When the concentrate B was fed, the milk quantity amounted to 21.99 L/day and was statistically significantly (P<0.05) greater than the milk quantity in case of feeding the concentrate A, when the milk quantity was 19.12 L/day. No statistically significant differences (P<0.05) of the protein and fat content in the milk were established.
Ključne besede: milking cows, concentrate, milk quantity, proteins, fats
Objavljeno: 10.07.2017; Ogledov: 21; Prenosov: 0
.pdf Polno besedilo (275,28 KB)

Quality and delivery of milk in Slovenia
Marjan Janžekovič, Maksimiljan Brus, Lidija Mužerlin, 2007, izvirni znanstveni članek

Opis: Milk production represents the possibility of earning monthly income and assures social security to many farms in Slovenia. In Slovenia the European rules and regulations on the quality of the delivered milk have been introduced, relating to the hygienic quality of milk and the count of somatic cells. The purchase price of the milk depends also on the protein and fat content. The aim of the research was to establish, whether the quality of the delivered milk complies with the prescriptions regulated by the Slovene legislation. The quality of the delivered milk in the area of the Šentjur agricultural cooperative (ACŠ) and in the entire area of Slovenia (SLO) has been studied. The bacteriological data in the individual quality classes, the data on the total count of somatic cels and the data on the fat and protein contents have been analyzed. 36 monthly accounts have been included in statistical processing. It has been established that the delivered milk of the areas in question does not differ in the relevant quality values.
Ključne besede: cattle, milk quality, fats, proteins, micro-organisms, somatic cells
Objavljeno: 10.07.2017; Ogledov: 46; Prenosov: 0
.pdf Polno besedilo (337,54 KB)

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