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41.
The effects of addition of cellular fibronectin on the cell-to-substrate contacts of a non-transformed adhesion-defective mutant, AD6, of the BALB/ c3T3 cell-line, and of transformed L-929 fibroblasts have been examined by interference reflection microscopy (IRM). We report that formation of the close contact, but not focal contacts, is promoted in parallel with an increase in spreading in both cell types. These results provide strong evidence for a functional role of fibronectin in the formation of the adhesive close contact.  相似文献   
42.
The mouse 3T3-L1 fibroblastic cell line rapidly differentiates to an adipocyte phenotype when post-confluent cells are treated for 48 h in fetal calf serum-containing medium supplemented with 1 microM dexamethasone (D), 0.5 mM methylisobutylxanthine (M) and 10 micrograms/ml insulin (I). D and I act synergistically to commit the cells to differentiate 24-48 h after initiating treatment, and this is blocked by the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate. In order to identify cellular proteins involved in the differentiation process we analyzed differentiating 3T3-L1 cells using two-dimensional electrophoresis on large format gels. We observed changes in over 300 proteins during differentiation (over 100 within 5 h of initiating differentiation) and many of these are also changed at the level of mRNA (by analysis of in vitro translation products). About 75% of the initial changes were maximally induced by treatment with a combination of M and I, while no more than 10 proteins and their corresponding mRNAs were maximally induced by D within 3.5 h. Another 10 proteins were synergistically regulated by the combination of all three agents (DMI) within 3.5 h. Additional species were induced at later times. Five of these were synergistically induced by treatments that lead to differentiation, were first expressed at elevated levels during commitment and remained elevated in fully differentiated adipocytes. One or more of these proteins could well have a functional role in the commitment to and/or expression of the adipocyte differentiation program.  相似文献   
43.
Vitellogenin has been identified in the ant Camponotus festinatus, both in queens and workers. In the workers, it is already present before adult eclosion in low concentrations (less than 1 microgram/microliter hemolymph). Vitellogenin and vitellin are immunologically identical and are composed of a single type of apoprotein with an apparent Mr = 185,000. The molecular weight of the native molecules was estimated as approximately 460,000 by pore limiting gradient electrophoresis. Vitellogenin was detected as a major protein in the hemolymph of young workers, both under queenright and queenless conditions. Thus, in spite of their sterility in the presence of the queen, C. festinatus workers are able to synthetize vitellogenin which is identical both in size and immunologically to the queen vitellogenin. About 6-7 weeks after adult eclosion, however, vitellogenin was usually undetectable in the hemolymph of queenright workers, particularly the minor workers, while it constituted about 30% of total protein in queenless workers. Protein concentration in the hemolymph of queenless insects increased up to 20-fold as compared to 1-day-old insects. Queenless workers also developed large amounts of perivisceral fat body, while queenright workers, particularly the minor workers, showed a dramatic fat body regression about 6 weeks after emergence.  相似文献   
44.
Three forms of glutamate dehydrogenase have been isolated from developing soybean seed. Their intracellular locations could not be determined directly because organelles and marker enzymes showed abnormal distribution on sucrose density gradient fractionation. By analogy with enzymes from other parts of the plant, glutamate dehydrogenase 2 was shown to be located in chloroplasts and glutamate dehydrogenase 3 in mitochondria. Glutamate dehydrogenase 1 could not be located in this way because it is found only in the seed. The three enzymes are similar in pH optima, molecular weight and substrate specificity with respect to 2-oxoglutarate and l-glutamate. The mitochondrial enzyme is specific for NAD+. The chloroplast enzyme shows low activity with NADP+ relative to NAD+ but uses NADPH readily in the aminating direction. Glutamate dehydrogenase 1 is active with both nucleotides and is the only form to show substantial deaminating activity with NADP+. Glutamate dehydrogenases 1 and 2 are activated and stabilized by glutathione and 2-mercaptoethanol whereas enzyme 3 is unaffected. No significant metabolic control of any of the enzymes could be detected. Malate, citrate, adenine nucleotides and long-chain fatty acyl CoA derivatives gave slight inhibition at high concentrations. Amino acids had no effect on activity. A possible role for the enzyme characteristic of the developing seed is discussed in relation to nutrient supply during the accumulation of reserve materials in the seed.  相似文献   
45.
Natural killer (NK) cell activity and interferon levels have been measured in the peripheral blood of children acutely ill with Plasmodium falciparum infection. The NK cell levels were found to be raised in the malaria-infected children, with a positive correlation between the degree of parasitemia and lytic activity. Comparatively high titers of antiviral activity was discovered in sera from the majority of P. falciparum-infected children, again positively correlating with the degree of parasitemia and NK levels. The characteristics of the antiviral factor indicated alpha-type interferon to be the dominating agent involved. Addition of exogenous interferon in vitro potentiated the NK levels of PBL from normal children while having no significant impact on cells from malaria-infected children.  相似文献   
46.
When C57BL/6 mice were injected iv with BCG in an oil-in-saline emulsion, they developed intense pulmonary granulomatous inflammation (PGI) and splenomegaly as well as chemotactic activity for macrophages and angiotensin-converting enzyme (ACE) in their lung fluids. PGI, splenomegaly, and levels of chemotactic activity and ACE were markedly reduced in T-cell-deficient “B” mice. The capacity to develop PGI was fully restored and splenomegaly was partially restored in “B” mice by the provision of syngeneic thymocytes, spleen cells, or purified T cells. These results indicate that the full expression of BCG-induced PGI is dependent upon thymus-derived cells and is associated with high levels of chemotactic activity for macrophages and ACE in the lung lavage fluid. Although BCG-induced splenomegaly appears to be T cell dependent, it did not reach its full magnitude in reconstituted “B” mice.  相似文献   
47.
Inhibition of rat skeletal muscle adenylate deaminase by creatine phosphate reported previously is due to inorganic pyrophosphate present as a contaminant in commercial preparations of creatine phosphate. This conclusion is based on the following evidence: a compound that inhibits adenylate deaminase can be separated from commercially prepared creatine phosphate by ion exchange chromatography; the inhibition by "creatine phosphate" and by the separated inhibitory compound is relieved by treatment with inorganic pyrophosphatase; inhibition by inorganic pyrophosphate is similar to that produced by unpurified creatine phosphate; and pyrophosphate is present in commercially available creatine phosphate in amounts sufficient to account for the inhibition. Some commercial preparations of creatine phosphate contain much less pyrophosphate than others; these preparations are only weakly inhibitory. Inorganic triphosphate is a more powerful inhibitor of the enzyme than pyrophosphate; it may also be present as a contaminant in creatine phosphate.  相似文献   
48.
49.
The relative proportions of carbonyl, O-acetyl, and O-(methylthio)methylsugars resulting from the partial oxidation of methyl α-D-glucopyranoside with methyl sulphoxide and acetic anhydride have been investigated@ the preparation of the 2- and 6-(methylthio)methyl ethers of methyl α-D-glucopyranoside is described.  相似文献   
50.
Trinitrophenyl groups have been specifically introduced into the alpha- and/or the epsilon-NH2 groups of glucagon by reaction with trinitrobenzenesulfonic acid. Introduction of this group into the epsilon-NH2 position of the hormone leads to an apparant increase in the helical content as measured by circular dichroism, while substitution on the alpha-NH2 position causes little change in this property. The usefulness of the trinitrophenyl group for the study of intramolecular singlet excitation transfer from tryptophan is suggested. The pK and reactivity of the amino groups, as measured by the pH dependence of the rate of reaction with trinitrobenzenesulfonic acid, showed that the two amino groups of glucagon have similar properties to those of small model peptides. The trinitrophenyl-glucagon derivatives have little or no activity in stimulating adenylyl cylase of rat liver. By comparison with previously reported results, this demonstrates that the effect of chemical modifications of the amino group on the biological activity of glucagon depends critically on the group which is introduced.  相似文献   
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