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901.
Proline transport in Kirsten sarcoma virus-transformed BALB 3T3 (Ki-3T3) cells was increased approximately twofold by 0.5 mm dibutyryl cAMP (dbcAMP), and the increase was observed whether transport was assayed in the presence or absence of cycloheximide. Two days of exposure to the analog was required for maximum stimulation. Increased proline transport contributed almost entirely to the increased incorporation of [14C]proline into noncollagen protein but for only 13% of the increased incorporation into collagen of dbcAMP-treated Ki-3T3 cells. Proline transport was further characterized using an assay system containing 0.1 mm cycloheximide, which did not affect transport over a 30-min period. The Km for proline was decreased from 6.5 to 3.4 mm by dbcAMP treatment of Ki-3T3. Proline transport in Ki-3T3 proceeds almost entirely via the A system, and the effect of dbcAMP appears to be on this system specifically since glycine and glutamine transport, which are heterogeneous, were not affected but transport of N-methylaminoisobutyrate, a specific A system substrate, was increased by dbcAMP treatment. Although 0.5 mm butyrate increased proline transport in Ki-3T3 cells to a similar degree as dbcAMP, the effect of the latter appeared related to its action as a cAMP analog since N6-monobutyryl cAMP, having a stable butyryl group, and 8-bromo-cAMP also increased proline transport while dbcGMP did not. The rate of proline transport in normal BALB 3T3 cells was only 30–40% lower than that of Ki-3T3 cells at various growth stages, and dbcAMP and 8-bromo-cAMP treatment also increased proline transport in the normal cells. The results of these studies suggest that dbcAMP and other cAMP analogs induce the synthesis of an altered component of the A system for amino acid transport and that the effect of these compounds is unrelated to the effect of transformation on proline transport. 相似文献
902.
Histone synthesis and deposition in the G1 and S phases of hepatoma tissue culture cells 总被引:7,自引:0,他引:7
Hepatoma tissue culture cells were synchronized in G1 and in S phase in order to examine the level of synthesis of different histone types and to determine the rate, timing, and location of their deposition onto DNA. We observe a basal level of synthesis in G1 (5% of that seen in S phase) for H2A.1, H2A.2, H3.2, H2B, and H4. The minor histone variants X and Z are synthesized at 30% of the rate observed in S cells. The rate of synthesis of the ubiquinated histones uH2A.1,2 is not as depressed in G1 cells as seen for H2A.1 and H2A.2. Histones synthesized in G1 are not deposited on the DNA of these cells at equivalent rates. Thus, histones H3.2 and H4 are not deposited significantly until S phase begins, at which time deposition occurs selectively on newly synthesized DNA. The deposition of H2A.1, H2A.2, H2B, X, and Z proceeds in G1; however, it occurs to a 2-4-fold lower extent than seen for the deposition of H1, HMG 14, and HMG 17. The deposition of all histones synthesized in S phase occurs rapidly, but there are variations in the sites of deposition. Thus, newly synthesized H3.1, H3.2, and H4 deposit primarily on newly replicated DNA whereas H2A.1, H2A.2, uH2A.1, 2, and H2B deposit only partially on new DNA (30%) and mostly on old. H1, HMG 14, and HMG 17 are deposited in an apparently fully random manner over the chromatin. To interpret these observations, we propose a model which includes a measure of histone exchange on the chromatin fiber. The model emphasizes the dynamics of histone-histone and histone-DNA interactions in regions of active genes and at replication forks. 相似文献
903.
Using pancreatic RNAase and RNAase from Act. rimosus as models, the effect of modification by azocombination on the catalytic properties of enzymes were studied. It was shown that RNAases binding to soluble dextran did not cause any significant changes in their major catalytic properties, when polymeric RNA was used as a substrate. At the same time, the physico-chemical properties of the modified enzymes may result in changes in the catalytic properties in a reaction with low molecular weight substrates. Evidence for this observation can be obtained from the increase in the synthetic activity of modified pancreatic RNAase as compared to the hydrolase activity in the dinucleotide synthesis reaction. 相似文献
904.
905.
S. Goldenberg J.M. Salles V.T. Contreras M.P.Lima Franco A.M. Katzin W. Colli C.M. Morel 《FEBS letters》1985,180(2):265-270
The cell-free translation products of polyribosomal and post-polyribosomal mRNAs from the non-infective epimastigotes and the infective metacyclic trypomastigotes of the parasitic protozoan Trypanosoma cruzi were compared by two-dimensional polyacrylamide gel electrophoresis. The result show that although many polypeptides are conserved, quantitative and qualitative differences are observed between both differentiation stages. The results also indicate the existence of post-polyribosomal mRNAs in equilibrium with polyribosomal counterparts. The immunoprecipitation of the in vitro synthesized polypeptides with chagasic human serum and the serum raised against an 85-kDa glycoprotein (P2-WGA), potentially involved in the process of T. cruzi penetration into mammalian cells, shows that while the chagasic serum recognizes the same 72-kDa, 68-kDa and 46-kDa polypeptides in both differentiation stages, the anti-P2-WGA serum immunoprecipitates a single 48-kDa polypeptide from in vitro translation products of metacyclic trypomastigotes. 相似文献
906.
A range of wheat cultivars with resistance factors effective against Puccinia recondita f. sp. tritici was studied to investigate the mode of action and expression of resistance at first and third seedling leaf stages. In most cultivars, resistance to isolate 74/2 resulted in extremely low levels of infection, apparently linked with a predominantly hypersensitive response by the host. In seedlings of cultivars Mans Fundin and Sterna, however, race-specific resistance was expressed as increased pathogen latent period and intermediate infection levels. 相似文献
907.
A Rhalem K Bekhti C Bourdieu G Luffau P Péry 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1989,309(1):19-23
Proteins are released from the surface of sporozoites of Eimeria falciformis during their in vitro incubation in a detergent solution. Some of these proteins reacted with antibodies from infected mice and specifically stimulated the proliferation of mesenteric lymph node cells of these mice. Oral immunization of mice with liposome encapsulated sporozoite surface antigens protected mice against a challenge infection. Two proteins (M.W. 27 and 180 K) induced an antibody synthesis in these vaccinated mice. 相似文献
908.
909.
Glycosylated haemoglobin (HbA1) was measured in seven insulin-dependent diabetic patients before, during, and after a seven-day period of monitored poor control. There was considerable individual variation in the pattern and degree of change in HbA1 concentration induced by poor control and the time when it occurred. Greater increases in HbA1 were seen during the period of metabolic derangement than in the subsequent two months. More information is required before HbA1 estimations are widely used clinically to monitor control in individual diabetics. 相似文献
910.
The results of the phage typing of 5, 168 Staph. aureus strains isolated in a surgical hospital between 1959 and 1977 are analyzed for each year of this period. The wave of increase in the number of staphylococci belonging to phage group II which began, as discovered in this study, in 1965 and still showed no tendency towards decrease in 1977, as well as the periodicity of rises and falls in the number of staphylococci belonging to phage groups I and III are discussed and compared with the data contained in the literature. The authors come to the conclusion that Staph. aureus is subject to wave-like rises and falls in the number of strains belonging to the main phage groups of the species, and among them the strains belonging to phage groups I and III seem to be inversely related in respect of rises and falls in number, such changes occurring periodically at an interval of 10-12 years, while in the strains belonging to phage group II changes in number occur at a slower rate. The constant account of the percentage of phage groups I, II and III is recommended to ensure rational antibiotic therapy. 相似文献