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81.
A theoretical model of intracellular devitrification 总被引:3,自引:0,他引:3
Karlsson JO 《Cryobiology》2001,42(3):154-169
Devitrification of the intracellular solution can cause significant damage during warming of cells cryopreserved by freezing or vitrification. Whereas previous theoretical investigations of devitrification have not considered the effect of cell dehydration on intracellular ice formation, a new model which couples membrane-limited water transport equations, classical nucleation theory, and diffusion-limited crystal growth theory is presented. The model was used to explore the role of cell dehydration in devitrification of human keratinocytes frozen in the presence of glycerol. Numerical simulations demonstrated that water transport during cooling affects subsequent intracellular ice formation during warming, correctly predicting observations that critical warming rate increases with increasing cooling rate. However, for cells with a membrane transport activation energy less than approximately 50 kJ/mol, devitrification was also affected by cell dehydration during warming, leading to a reversal of the relationship between cooling rate and critical warming rate. Thus, for low warming rates (less than 10 degrees C/min for keratinocytes), the size and total volume fraction of intracellular ice crystals forming during warming decreased with decreasing warming rate, and the critical warming rate decreased with increasing cooling rate. The effects of water transport on the kinetics of intracellular nucleation and crystal growth were elucidated by comparison of simulations of cell warming with simulations of devitrification in H(2)O-NaCl-glycerol droplets of constant size and composition. These studies showed that the rate of intracellular nucleation was less sensitive to cell dehydration than was the crystal growth rate. The theoretical methods presented may be of use for the design and optimization of freeze-thaw protocols. 相似文献
82.
The complete set of genes encoding major intrinsic proteins in Arabidopsis provides a framework for a new nomenclature for major intrinsic proteins in plants 总被引:27,自引:0,他引:27
Johanson U Karlsson M Johansson I Gustavsson S Sjövall S Fraysse L Weig AR Kjellbom P 《Plant physiology》2001,126(4):1358-1369
Major intrinsic proteins (MIPs) facilitate the passive transport of small polar molecules across membranes. MIPs constitute a very old family of proteins and different forms have been found in all kinds of living organisms, including bacteria, fungi, animals, and plants. In the genomic sequence of Arabidopsis, we have identified 35 different MIP-encoding genes. Based on sequence similarity, these 35 proteins are divided into four different subfamilies: plasma membrane intrinsic proteins, tonoplast intrinsic proteins, NOD26-like intrinsic proteins also called NOD26-like MIPs, and the recently discovered small basic intrinsic proteins. In Arabidopsis, there are 13 plasma membrane intrinsic proteins, 10 tonoplast intrinsic proteins, nine NOD26-like intrinsic proteins, and three small basic intrinsic proteins. The gene structure in general is conserved within each subfamily, although there is a tendency to lose introns. Based on phylogenetic comparisons of maize (Zea mays) and Arabidopsis MIPs (AtMIPs), it is argued that the general intron patterns in the subfamilies were formed before the split of monocotyledons and dicotyledons. Although the gene structure is unique for each subfamily, there is a common pattern in how transmembrane helices are encoded on the exons in three of the subfamilies. The nomenclature for plant MIPs varies widely between different species but also between subfamilies in the same species. Based on the phylogeny of all AtMIPs, a new and more consistent nomenclature is proposed. The complete set of AtMIPs, together with the new nomenclature, will facilitate the isolation, classification, and labeling of plant MIPs from other species. 相似文献
83.
84.
Beauchemin N Draber P Dveksler G Gold P Gray-Owen S Grunert F Hammarström S Holmes KV Karlsson A Kuroki M Lin SH Lucka L Najjar SM Neumaier M Obrink B Shively JE Skubitz KM Stanners CP Thomas P Thompson JA Virji M von Kleist S Wagener C Watt S Zimmermann W 《Experimental cell research》1999,252(2):243-249
85.
Carina Johansson Anders Pedersen B G?ran Karlsson Jan Rydstr?m 《European journal of biochemistry》2002,269(18):4505-4515
Membrane-bound transhydrogenases are conformationally driven proton-pumps which couple an inward proton translocation to the reversible reduction of NADP+ by NADH (forward reaction). This reaction is stimulated by an electrochemical proton gradient, Delta p, presumably through an increased release of NADPH. The enzymes have three domains: domain II spans the membrane, while domain I and III are hydrophilic and contain the binding sites for NAD(H) and NADP(H), respectively. Separately expressed domain I and III together catalyze a very slow forward reaction due to tightly bound NADP(H) in domain III. With the aim of examining the mechanistic role(s) of loop D and E in domain III and intact cysteine-free Escherichia coli transhydrogenase by cysteine mutagenesis, the conserved residues beta A398, beta S404, beta I406, beta G408, beta M409 and beta V411 in loop D, and residue beta Y431 in loop E were selected. In addition, the previously made mutants betaD392C and betaT393C in loop D, and beta G430C and beta A432C in loop E, were included. All loop D and E mutants, especially beta I406C and beta G430C, showed increased ratios between the rates of the forward and reverse reactions, thus approaching that of the wild-type enzyme. Determination of values indicated that the former increase was due to a strongly increased dissociation of NADPH caused by an altered conformation of loops D and E. In contrast, the cysteine-free G430C mutant of the intact enzyme showed the same inhibition of both forward and reverse rates. Most domain III mutants also showed a decreased affinity for domain I. The results support an important and regulatory role of loops D and E in the binding of NADP(H) as well as in the interaction between domain I and domain III. 相似文献
86.
Johan?UddlingEmail author H?kan?Pleijel Per?Erik?Karlsson 《Trees - Structure and Function》2004,18(6):686-695
Leaf diffusive conductance for water (gl) and twig xylem pressure (xt) was measured in juvenile silver birch, Betula pendula, under field conditions in southern Sweden. Data from one site were used to parameterise two different multiplicative models for gl (dependent data), and measurements from another site were used to validate these models (independent data). In addition, experiments were performed in controlled environments to validate the gl response functions used in the models. The driving variables in the D-model were photosynthetic photon flux density, air temperature and water vapour pressure deficit of the air (Da), while the DH-model also included the accumulated hours after sunrise each day with Da above a certain threshold (H). Both models satisfactorily predicted the variation in gl in dependent as well as in independent data, and the gl response functions used were supported by the experiments in controlled environments. The DH-model was more successful in predicting gl than the D-model by accounting for the observation that gl was lower at higher H under similar weather conditions. There was a considerable variation in maximum gl during the season, as well as between the two sites. On relatively warm and dry days xt rapidly declined during the morning and then stabilized around a constant value until the late afternoon, with the stomatal regulation effectively preventing xt from decreasing below this value. We suggest that these models could be used to simulate the gl in juvenile birch if maximum gl is locally estimated and if the response functions are not extrapolated beyond the climate range for this study. 相似文献
87.
Karlsson R 《Journal of molecular recognition : JMR》2004,17(3):151-161
PubMed searches identified four emerging application areas for surface plasmon resonance systems. Food analysis, proteomics, immunogenicity and drug discovery. These application areas are reviewed. In connection with the review of drug discovery applications a case study is presented. This study demonstrates the value of combining results from drug-target and ADME predictive assays for compound selection. 相似文献
88.
Studies on gangliosides with affinity for Helicobacter pylori: binding to natural and chemically modified structures 总被引:1,自引:0,他引:1
Miller-Podraza H Johansson P Angström J Larsson T Longard M Karlsson KA 《Glycobiology》2004,14(3):205-217
Helicobacter pylori, like many other microbes, has the ability to bind to carbohydrate epitopes. Several sugar sequences have been reported as active for the bacterium, including some neutral, sulfated, and sialylated structures. We investigated structural requirements for the sialic acid-dependent binding using a number of natural and chemically modified gangliosides. We have chosen for derivatization studies two kinds of binding-active glycolipids, the simple ganglioside S-3PG (Neu5Ac alpha 3Gal beta 4GlcNAc beta 3Gal beta 4Glc beta 1Cer, sialylparagloboside) and branched polyglycosylceramides (PGCs) of human origin. The modifications included oxidation of the sialic acid glycerol chain, reduction of the carboxyl group, amidation of the carboxyl group, and lactonization. Binding experiments confirmed a preference of H. pylori for 3-linked sialic acid and penultimate 4-linked galactose. As expected, neolacto gangliosides (with Gal beta 4GlcNAc in the core structure) were active in our assays, whereas gangliosides with lacto (Gal beta 3GlcNAc) and ganglio (Gal beta 3GalNAc) carbohydrate chains were not. Negative binding results were also obtained for disialylparagloboside (with terminal NeuAc alpha 8NeuAc) and NeuAc alpha 6-containing glycolipids. Chemical studies revealed dependence of the binding on Neu5Ac and its glycerol and carboxyl side chains. Most of the derivatizations performed on these groups abolished the binding; however, some of the amide forms turned out to be active, and one of them (octadecylamide) was found to be an excellent binder. The combined data from molecular dynamics simulations indicate that the binding-active configuration of the terminal disaccharide of S-3PG is with the sialic acid in the anticlinal conformation, whereas in branched PGCs the same structural element most likely assumes the synclinal presentation. 相似文献
89.
90.
Actin polymerization is a prominent feature of migrating cells, where it powers the protrusion of the leading edge. Many studies have characterized the well-ordered and dynamic arrangement of filamentous actin in this submembraneous space. However, less is known about the organization of unpolymerized actin. Previously, we reported on the use of covalently coupled profilin:actin to study actin dynamics and presented evidence that profilin-bound actin is a major source of actin for filament growth. To locate profilin:actin in the cell we have now used this non-dissociable complex for antibody generation, and obtained monospecific anti-actin and anti-profilin antibodies from two separate immunizations. Fluorescence microscopy revealed drastic differences in the staining pattern generated by the anti-actin antibody preparations. With one, distinct puncta appeared at the actin-rich leading edge and sometimes aligned with microtubules in the interior of the lamella, while the other displayed typical actin filament staining. Labelling experiments in vitro demonstrated failure of the first antibody to recognize filamentous actin and none of the two bound microtubules. The two anti-profilin antibodies purified in parallel generated a punctated pattern similar to that seen with the first anti-actin antibody. All antibody preparations labelled the nuclei. 相似文献