Showing papers on "Cellular compartment published in 1978"
TL;DR: Reconstructed morphological sequences and the finding of SV40 in different spaces of the cell suggest that entry of SV 40 into the different compartments and eventually into the site of replication is facilitated by its capacity for being enveloped by a variety of membranes and the sequential fusion and fission of these membranes.
Abstract: Permissive and nonpermissive simian virus 40 (SV40)-infected cells were ultrastructurally analyzed. Viral particles were found in the cytoplasm, rough endoplasmic reticulum, nuclear envelope, lysosomes, and mitochondria. Upon entering the cell the virion obtains a tight membrane envelope. It seems to be either released from the envelope upon fusion with other membranes of the cell or aggregated into tubular membrane specializations upon fusion with other membrane-enveloped particles. Reconstructed morphological sequences and the finding of SV40 in different spaces of the cell suggest that entry of SV40 into the different compartments and eventually into the site of replication is facilitated by its capacity for being enveloped by a variety of membranes (notably the cell membrane and the nuclear membrane) and the sequential fusion and fission of these membranes.
67 citations
TL;DR: In the in vitro experiments, higher serum radioactivity alone could not account for increases in the hepatic nuclear 125I in the hypothyroid rats because cytosol 125I (presumably in dynamic exchange with both blood and nuclei) was less, Consequently, cytOSol T3-binding proteins may regulate the free T3 concentration in the cell and, thus influence the distribution of the hormone in other cellular compartments.
Abstract: A tracer dose of [125I]T3 was given iv to normal, thyroidectomized, and propylthiouracil-fed rats and the distribution of radioactivity in serum and liver fractions was studied over 1 h. Total liver homogenate and serum 125I were higher at all times in hypothyroid rats and, in all groups, showed a continuous fall over the period studied. Hepatic nuclear 125I was maximal at 20 min in all and was greater in hypothyroid rats; there was more 125I in the hepatic cytosol of normal rats than in that from either thyroidectomized or propylthiouracil-fed animals. Binding studies with [125I]T3 and purified hepatic neclear preparations in vitro indicated that both the association constant, Ka (1.08-9.0 x 10(9) M-1) and the capacity (500-600 pg/mg DNA) in thyroidectomized and goitrogen-treated rats were similar to those obtained with normal animals. Cytosol, on the other hand, showed a decrease in binding capacity without change in affinity in livers of hypothyroid rats. Analysis of binding data by Hill plots indicated the presence of both positive and negative cooperativity in binding of T3 by rat liver cytosol proteins. In the in vitro experiments, higher serum radioactivity alone could not account for increases in the hepatic nuclear 125I in the hypothyroid rats because cytosol 125I (presumably in dynamic exchange with both blood and nuclei) was less. Consequently, cytosol T3-binding proteins may regulate the free T3 concentration in the cell and, thus influence the distribution of the hormone in other cellular compartments.
19 citations
TL;DR: High cell concentrations decreased transport and protein synthesis as a result of isotopic dilution of labelled amino acids with those released by the hepatocytes, consistent with the capacity of naturally occurring amino acids to compete with alpha-aminoisobutyric acid for uptake into the hepatocyte.
19 citations
TL;DR: The complete absence of glycolytic enzymes from brush-border vesicles, which had retained part of their original content, indicates that the brush border does not contain glycoleytic enzymes in vivo and can be thought of as a compartment of its own, somehow separated from the cytoplasm.
Abstract: Activities of four enzymes of the glycolytic pathway, hexokinase, glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase, were determined in a vesicular brush-border preparation from rabbit kidneys. The specific activities of the enzymes were decreased several-hundredfold in the brush-border preparation compared with a kidney homogenate, but the enzymes were not totally absent. Density-gradient centrifugation of the brush-border preparation yielded brush border of even higher purity and also a characteristic pattern of distribution for each of the contaminating intracellular membranes. The presence of hexokinase in the brush-border preparation could be traced to contaminating mitochondria, and that of glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase to contaminating vesicles derived from the endoplasmic reticulum. The brush-border vesicles contained some ATP. An intravesicular concentration of 0.1mm was estimated, indicating that the vesicles had retained at least a part of their original content. Experiments in which fluorescein isothiocyanate-dextran (mol.wt. 20000) was present during cell lysis revealed that much, but not all, of the brush-border contents had been exchanged with the medium. The complete absence of glycolytic enzymes from brush-border vesicles, which had retained part of their original content, indicates that the brush border does not contain glycolytic enzymes in vivo and can be thought of as a compartment of its own, somehow separated from the cytoplasm.
5 citations