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71.
Because the liver is the major organ responsible for removal of soluble immune complexes (IC), the surface binding characteristics of preformed model IC to unstimulated mouse liver nonparenchymal cells (NPC) in suspension were studied. NPC of non-autoimmune C3H/FeJ, C3H/HeJ, A/J, DBA/2 and the autoimmune NZB/W F1 and MRL/lpr female mice of various ages were isolated by perfusion of the portal vein with collagenase followed by separation of NPC from hepatocytes with a metrizamide gradient. Thirty-five percent of NPC of all mouse strains were nonspecific esterase-positive and phagocytosed latex beads. Radiolabeled mouse IgG anti-DNP covalently cross-linked stable IC were separated by gel filtration and bound to NPC under various conditions. Marked differences were noted in maximal number of IC bound per cell between the autoimmune and non-autoimmune mouse strains: 3.3 to 4.0 X 10(5) in the non-autoimmune strains vs 0.3 to 1.4 X 10(5) molecules of IC bound per cell in the autoimmune strains at 1 to 6 mo. Insignificant differences were noted in Ka by Scatchard plot analysis (3.5 to 5.0 X 10(8) M-1) and rate of reversibility of binding as determined by dissociation of surface-bound IC with an excess of heat-aggregated gamma-globulin (T 1/2:1.5 to 2 min). These data demonstrate a decreased number of available binding sites for IC in unstimulated NPC from NZB/W F1 and MRL/lpr female mice throughout their life spans. Although the findings are consistent with saturation of binding sites of the NPC with native IC, the abnormality found in the 1-mo-old autoimmune mice (who do not have detectable autoantibodies) suggests a primary defect in FC receptor expression or an altered state of activation of NPC that may contribute to the disease process.  相似文献   
72.
The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K+, Ca2+ and Mg2+ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.  相似文献   
73.
N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).  相似文献   
74.
A PROCESS called “excitation-contraction coupling” has been generally accepted to take place only in the direction of excitation to contraction. Through this mechanism a propagated action potential initiates an active state in skeletal or cardiac muscle and the muscle contracts. We propose that, in the mammalian ventricular myocardium at least, the process is not unidirectional and an important reverse coupling between the contractile system and the excitable plasma membrane has been overlooked. Through this feedback interaction the mode of contraction (that is, isotonic or isometric) not only determines the instantaneous electrical state of the plasma membrane, but also influences the mechanical events of the subsequent beats. Thus when Kaufmann et al.1 recorded intracellular action potentials from cat papillary muscle, the time course of the repolarization was altered depending on the mode of contraction. Some kind of contraction-excitation feedback has also been suggested by Stauch2 and Lab3,4. They showed a difference in the shape of the monophasic action potential, as recorded by a suction electrode, when comparing isotonic and isovolumic contraction of the intact ventricle. But their experimental conditions did not allow satisfactory analysis of the phenomenon.  相似文献   
75.
76.
Sokawa et al. suggest that rel- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.  相似文献   
77.
A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells.  相似文献   
78.
Kimball and Wilson1 reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen2 observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators3 had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore4 reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler5 has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore.  相似文献   
79.
JACOB and Fuerst1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ3 which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli2 and one would therefore expect its substrate to be murein.  相似文献   
80.
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