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991.
A novel method was developed for the direct examination of pairwise encounters between positively and negatively charged
phospholipid bilayer vesicles. Giant bilayer vesicles (unilamellar, 4–20 μm in diameter) prepared from 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine, a new cationic phospholipid derivative, were electrophoretically maneuvered into contact with
individual anionic phospholipid vesicles. Fluorescence video microscopy revealed that such vesicles commonly underwent fusion
within milliseconds (1 video field) after contact, without leakage. Fusion occurred at constant volume and, since flaccid
vesicles were rare, the excess membrane was not available after fusion. Hemifusion (the outer monolayers of each vesicle fused
while the inner monolayers remained intact) was inferred from membrane-bound dye transfer and a change in the contact area.
Hemifusion was observed as a final stable state and as an intermediate to fusion of vesicles composed of charged phospholipids
plus zwitterionic phospholipids. Hemifusion occurred in one of three ways following adhesion: either delayed with an abrupt
increase in area of contact, immediately with a gradual increase in area of contact, or with retraction during which adherent
vesicles dissociated from a flat contact to a point contact. Phosphatidylethanolamine strongly promoted immediate hemifusion;
the resultant hemifused state was stable and seldom underwent complete fusion. Although sometimes single contacts between
vesicles led to rupture of both, in other cases, a single vesicle underwent multiple fusion events. Direct observation has
unequivocally demonstrated the fusion of two, isolated bilayer-bounded bodies to yield a stable, non-leaky product, as occurs
in cells, in the absence of proteins.
Received: 25 November 1998/Revised: 23 March 1999 相似文献
992.
993.
R Fleischmajer K Kuroda A Utani E Douglas MacDonald J S Perlish E Arikawa-Hirasawa K Sekiguchi N Sanzen R Timpl Y Yamada 《Matrix biology》2000,19(7):637-647
The purpose of this study was to determine the mRNA and protein expression of laminin alpha chains at various stages of in vitro skin morphogenesis. Fibroblasts in mono-cultures express low levels of the mRNA of laminin alpha1,alpha2, alpha3 and alpha4 chains. When co-cultured with keratinocytes for 28 days, they expressed the mRNA for all these chains. Keratinocytes in monolayer expressed the laminin alpha3 chain mRNA and very low levels of the mRNA of the alpha1 and alpha2 chains, although, when recombined with fibroblasts they also expressed laminin alpha1and alpha2 mRNA, but not the laminin alpha4 mRNA. Immunocytochemistry of cells in co-culture showed that laminin alpha1, alpha3 and alpha5 chains were expressed in the epidermis, while the laminin alpha2, beta1, and gamma1 chains were noted in the dermis and at the epidermo-dermal interface. The laminin alpha1chain was first expressed during the proliferative stage (14-21 days) and the laminin alpha2 and alpha5 chains appeared later, during the differentiation stage (28-42 days). The above results suggest that epithelial-mesenchymal interactions are involved in the expression of laminin alpha chain mRNA during in vitro skin morphogenesis. In addition, there is distinct temporal and spatial expression of these chains during proliferative and differentiation stages, possibly reflecting different functions. 相似文献
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995.
Kyra J. Cowan Justin A. MacDonald Janet M. Storey Kenneth B. Storey 《Experimental Biology Online》2000,5(1):1-25
The maximal activities of 28 enzymes, representing multiple pathways of intermediary metabolism, were quantified in the brain, liver and skeletal muscle of spadefoot toads Scaphiopus couchii, comparing control toads with animals that had estivated for 2 months. Estivation-induced changes in brain enzyme activities were consistent with suppressed glycolysis and increased ketone body and amino acid catabolism. In liver, estivation resulted in reduced activities of eight enzymes representing carbohydrate, amino acid, ketone body and phosphagen metabolism, but the maximal activity of malic enzyme increased by 2.4-fold. Estivation led to a large-scale reorganization of skeletal muscle affecting most of the enzymes analyzed. Activities of enzymes of carbohydrate catabolism were generally elevated except for glycogen phosphorylase and hexokinase, whereas those of enzymes of fatty acid synthesis and ketone body metabolism were reduced. Increased glutamate dehydrogenase activities in both brain and muscle, as well as activities of other amino-acid-catabolizing enzymes in muscle, correlated with specific changes in the free amino acids pools in those tissues (reduced glutamine activity, increased glutamate, alanine and valine activities) that appear to be related to protein catabolism, for the purposes of elevating urea levels. The effects of estivation on signal transduction systems were also assessed. Total activities of protein kinases A and C (PKA and PKC) were largely unaltered in toad tissues during estivation (except for a 57% reduction in liver total PKC), but in seven organs there were strong reductions in the percentage of PKA present as the active catalytic subunit in estivating animals, and three contained a much lower percentage of membrane-bound active PKC during estivation. Activities of protein phosphatase types 1, 2A, 2B, and 2C were also frequently reduced during estivation. Overall, these results suggest that anuran estivation involves metabolic reorganization, including changing the maximal activities of key enzymes of intermediary metabolism as well as depressing the metabolic rate by suppressing signal transducing enzymes. 相似文献
996.
Katharine MacDonald 《Human nature (Hawthorne, N.Y.)》2007,18(4):386-402
This paper is a cross-cultural examination of the development of hunting skills and the implications for the debate on the
role of learning in the evolution of human life history patterns. While life history theory has proven to be a powerful tool
for understanding the evolution of the human life course, other schools, such as cultural transmission and social learning
theory, also provide theoretical insights. These disparate theories are reviewed, and alternative and exclusive predictions
are identified. This study of cross-cultural regularities in how children learn hunting skills, based on the ethnographic
literature on traditional hunters, complements existing empirical work and highlights future areas for investigation. 相似文献
997.
Paolo Biancheri Antonio Di Sabatino Gino R. Corazza Thomas T. MacDonald 《Cell and tissue research》2013,351(2):269-280
Serine proteases, cysteine proteases, aspartic proteases and matrix metalloproteinases play an essential role in extracellular matrix remodeling and turnover through their proteolytic action on collagens, proteoglycans, fibronectin, elastin and laminin. Proteases can also act on chemokines, receptors and anti-microbial peptides, often potentiating their activity. The intestinal mucosa is the largest interface between the external environment and the tissues of the human body and is constantly exposed to proteolytic enzymes from many sources, including bacteria in the intestinal lumen, fibroblasts and immune cells in the lamina propria and enterocytes. Controlled proteolytic activity is crucial for the maintenance of gut immune homeostasis, for normal tissue turnover and for the integrity of the gut barrier. However, in intestinal immune-mediated disorders, pro-inflammatory cytokines induce the up-regulation of proteases, which become the end-stage effectors of mucosal damage by destroying the epithelium and basement membrane integrity and degrading the extracellular matrix of the lamina propria to produce ulcers. Protease-mediated barrier disruption in turn results in increased amounts of antigen crossing into the lamina propria, driving further immune responses and sustaining the inflammatory process. 相似文献
998.
Oscillations, Intercellular Coupling, and Insulin Secretion in Pancreatic β Cells 总被引:2,自引:0,他引:2 下载免费PDF全文
Patrick E MacDonald 《PLoS biology》2006,4(2):e49
999.
1000.