The effect of ribonuclease on rat-liver ribosomes.
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ABSTRACT:
SUBMITTER: Brentani R
PROVIDER: S-EPMC1198493 | biostudies-other | 1968 Jan
REPOSITORIES: biostudies-other
Similar Datasets
Project description:Because it has been proposed that the ribosome-membrane interaction is different in endoplasmic reticulum derived from a non-secretory and secretory cell we undertook a study to determine whether attachment of the ribosome to the membrane involved ribosomal RNA and if the rRNA in ribosomes derived from the two classes of cell possessed an altered susceptibility to RNAase (ribonuclease) hydrolysis. We found that brain ribosomes appeared to possess more regions accessible to nuclease attack, independent of whether a sequence-dependent RNAase (T(1)) or a sterically hindered RNAase bound to Enzite polymer was employed. These results were independent of whether the ribosomes were membrane-bound or detached from the endoplasmic reticulum membranes, but at high RNAase concentration these differences became negligible. No conclusions, however, could be drawn as to whether ribosomal RNA is involved in the attachment of the ribosome to the endoplasmic reticulum membrane, because of the presence of endogeneous membrane-associated RNAases. Analysis of the rRNA fragments by polyacrylamide-gel electrophoresis suggests that the sites available for attack by low concentrations of nuclease in bound-ribosomes derived from brain cortex are different from those of liver.
| S-EPMC1165823 | biostudies-other
Project description:The mildest treatment with ribonuclease that causes any disaggregation of the polysomes of Escherichia coli or HeLa cells simultaneously attacks the RNA of the constituent ribosomes. It is concluded that the susceptibility to ribonuclease of polysomes does not suggest that they are held together by a strand of messenger RNA. The RNA of the larger sub-unit of bacterial ribosomes has particularly sensitive regions resulting in a non-random degradation. The RNA of the smaller sub-unit of E. coli ribosomes is relatively resistant to ribonuclease attack. The same may be true of the respective sub-units of the intact HeLa-cell ribosome, but both sub-units become very sensitive to ribonuclease on dissociation from each other.
| S-EPMC1198691 | biostudies-other
Project description:1. A comparison has been made between the ribonuclease activities of untreated ribosomes from Escherichia coli B and Pseudomonas fluorescens and the activities of ribosomes on to which ribosomal ribonuclease from E. coli B has been adsorbed. 2. The normal ribosomes from both species were stable in 5-10mm-Mg(2+) (I0.16) at pH6. The RNA in ribosomes from Ps. fluorescens was attacked by the adsorbed ribonuclease under these conditions, whereas the ribosomes from E. coli B were able to adsorb and inhibit this enzyme. 3. Inhibition was also observed with ribosomes from Aerobacter aerogenes, Proteus vulgaris and two other strains of E. coli. It was not observed in ribosomes from three species of Pseudomonas. 4. The inhibition depended on the integrity of the ribosomes and was not observed under conditions of low Mg(2+) concentration that cause irreversible degradation into more slowly sedimenting particles.
| S-EPMC1264755 | biostudies-other
Project description:1. Parts of the 16s and 30s RNA species of reticulocytes are readily hydrolysed by pancreatic ribonuclease. The biological activity of the ribosomes is diminished after treatment with low concentrations of the enzyme (e.g. 1ng. of ribonuclease/2.5mg. of polyribosome fraction/ml.). A high proportion of the chain scissions are ;hidden' owing to the secondary structure of the RNA moiety. 2. As the concentration of ribonuclease is increased RNA is lost from the ribosome. About 20-30% of the RNA may be removed from the ribosome without altering appreciably its sedimentation coefficient or its appearance in the electron microscope. 3. The amount of RNA removed from the ribosome is not increased by raising the concentration of enzyme from about 1mug. to 2.5mg. of ribonuclease/2.5mg. of polyribosome fraction/ml., or by increasing the temperature from 0 degrees to 30 degrees , or by first converting the RNA moiety into a single-stranded form before exposure to ribonuclease. 4. Untreated polyribosomes aggregate at about 75 degrees , whereas ribosomes treated with ribonuclease aggregate at about 45 degrees . The aggregates that are found on heating ribosomes after enzymic hydrolysis contain about 40-50% of the complement of RNA of intact ribosomes. 5. From the size of the fragments of RNA isolated from RNA-depleted ribosomes it is inferred that there is one site/60-100 nucleotides that is sensitive to ribonuclease. 6. The RNA moiety of RNA-depleted ribosomes has some double-helical character as shown by the optical properties and X-ray-diffraction pattern of ribonuclease-treated ribosomes and by the ;melting' properties of the isolated RNA. 7. Subparticles prepared by titration with an excess of EDTA are readily hydrolysed by ribonuclease to fragments of S(20,w) less than 4s, in contrast with the intact particle.
| S-EPMC1184962 | biostudies-other
Project description:The ribonuclease and phosphodiesterase activities of rat liver plasma membranes, purified from the crude nuclear fraction by centrifugation in an A-XII zonal rotor and flotation, were examined and compared. The plasma membrane is responsible for between 65 and 90% of the phosphodiesterase activity of the cell and between 25 and 30% of the particulate ribonuclease activity measured at pH8.7 in the presence of 7.5mm-MgCl(2). Both enzymes were most active between pH8.5 and 8.9. Close to the pH optimum, both enzymes were more active in Tris buffer than in Bicine or glycine buffer. Both plasma-membrane phosphodiesterase and ribonuclease were strongly activated by Mg(2+), there being at least a 12-fold difference between the activity in the presence of Mg(2+) and of EDTA. There is, however, a difference in the response of the enzymes to Mg(2+) and EDTA in that the phosphodiesterase is fully activated by 1.0mm-MgCl(2) and fully inhibited by 1.0mm-EDTA, whereas the ribonuclease requires 7.5mm-MgCl(2) for full activation and 5mm-EDTA for full inhibition. Density-gradient centrifugation has indicated that on solubilization in Triton X-100 most of the ribonuclease activity is released into a small fragment of the same size as that containing the phosphodiesterase activity. The relationship between the two activities is discussed in view of these results.
| S-EPMC1177608 | biostudies-other
Project description:Preparations of covalently closed mitochondrial DNA of rat liver contain 10-30% of molecules that are converted into relaxed circular molecules after treatment with ribonuclease. Control experiments, with covalently closed bacteriophage PM2 DNA, indicate that ribonuclease-sensitivity cannot be induced either by depurination or by incubation with reducing agents.
| S-EPMC1168061 | biostudies-other
Project description:1. The ;30s' and ;50s' ribosomes from ribonuclease-active (Escherichia coli B) and -inactive (Pseudomonas fluorescens and Escherichia coli MRE600) bacteria have been studied in the ultracentrifuge. Charge anomalies were largely overcome by using sodium chloride-magnesium chloride solution, I 0.16, made 0-50mm with respect to Mg(2+). 2. Differentiation of enzymic and physical breakdown at Mg(2+) concentrations less than 5mm was made by comparing the properties of E. coli B and P. fluorescens ribosomes. 3. Ribonuclease-active ribosomes alone showed a transformation of ;50s' into 40-43s components. This was combined with the release of a small amount of ;5s' material which may be covalently bound soluble RNA. Other transformations of the ;50s' into 34-37s components were observed in both ribonuclease-active and -inactive ribosomes at 1.0-2.5mm-Mg(2+), and also with E. coli MRE600 when EDTA (0.2mm) was added to a solution in 0.16m-sodium chloride. 4. Degradation of ribonuclease-active E. coli B ribosomes at Mg(2+) concentration 0.25mm or less was coincident with the formation of 16s and 21s ribonucleoprotein in P. fluorescens, and this suggested that complete dissociation of RNA from protein was not an essential prelude to breakdown of the RNA by the enzyme. 5. As high Cs(+)/Mg(2+) ratios cause ribosomal degradation great care is necessary in the interpretation of equilibrium-density-gradient experiments in which high concentrations of caesium chloride or similar salts are used. 6. The importance of the RNA moiety in understanding the response of ribosomes to their ionic environment is discussed.
| S-EPMC1207202 | biostudies-other
Project description:1. The size distribution of aggregates of liver ribosomes and their protein-synthesizing ability in vitro were studied shortly after X-irradiation of guinea pigs. 2. Sucrose-density-gradient analysis of the mitochondrial supernatant after treatment with deoxycholate revealed a gradual increase in the number of polysomes, reaching a maximum between 9 and 15 hr. after irradiation. At that period the amount of ribonucleoprotein particles reached a level 25-30% above the control. This finding was confirmed by analytical-ultracentrifugal analysis and electron microscopy. Experiments were conducted to exclude the possibility that the enrichment of polysomes in the irradiated animals had occurred during the isolation procedure. 3. The protein-synthesizing ability of total ribosomal particles was measured in vitro. This showed an increase in amino acid incorporation parallel to the progressive enrichment of polysomes. At radiation doses of up to 1000r. the protein-synthesizing capacity was dependent on the radiation dose: the higher the dose the higher the amino acid incorporation, reaching 40-60% above the control at the period of maximal polysome enrichment. Amino acid incorporation remained at this level after radiation doses of between 1000 and 3000r. The enhanced protein-synthesizing activity was due solely to the increase in the proportion of polysomes, since irradiation was without effect on the activity of single ribosomes. 4. The results of the experiments are discussed in the light of our knowledge of the effect of radiation on protein synthesis.
| S-EPMC1186935 | biostudies-other
Project description:Starvation of rats for several days led to marked decrease in cytoplasmic polysomes and accumulation of breakdown products having S values less than 200s. Re-feeding of the starved animals induced a rapid reassembly of polysomes. These newly formed polysomes, in the presence of actinomycin D, decayed in a biphasic fashion: about two-thirds decayed with an apparent half-life of 3-3(1/2)hr. but the other one-third were much more stable. Evidence that polysome decay is an accurate reflexion of messenger RNA stability is presented, and it is concluded that in the presence of large doses of actinomycin D, rat-liver cytoplasm contains messenger RNA classes of widely varying stability, the more stable class having a half-life of at least 80hr. The half-life of liver ribosomes was also determined and was found to be 110-127hr.
| S-EPMC1270442 | biostudies-other
Project description:Two important signaling pathways in liver fibrosis are the PDGF- and TGF? pathway and compounds inhibiting these pathways are currently developed as antifibrotic drugs. Testing antifibrotic drugs requires large numbers of animal experiments with high discomfort. Therefore, a method to study these drugs ex vivo was developed using precision-cut liver slices from fibrotic rat livers (fPCLS), representing an ex vivo model with a multicellular fibrotic environment. We characterized the fibrotic process in fPCLS from rat livers after 3 weeks of bile duct ligation (BDL) during incubation and tested compounds predominantly inhibiting the TGF? pathway (perindopril, valproic acid, rosmarinic acid, tetrandrine and pirfenidone) and PDGF pathway (imatinib, sorafenib and sunitinib). Gene expression of heat shock protein 47 (Hsp47), ? smooth muscle actin (?Sma) and pro-collagen 1A1 (Pcol1A1) and protein expression of collagens were determined. During 48 hours of incubation, the fibrosis process continued in control fPCLS as judged by the increased gene expression of the three fibrosis markers, and the protein expression of collagen 1, mature fibrillar collagen and total collagen. Most PDGF-inhibitors and TGF?-inhibitors significantly inhibited the increase in gene expression of Hsp47, ?Sma and Pcol1A1. Protein expression of collagen 1 was significantly reduced by all PDGF-inhibitors and TGF?-inhibitors, while total collagen was decreased by rosmarinic acid and tetrandrine only. However, fibrillar collagen expression was not changed by any of the drugs. In conclusion, rat fPCLS can be used as a functional ex vivo model of established liver fibrosis to test antifibrotic compounds inhibiting the PDGF- and TGF? signalling pathway.
| S-EPMC3995767 | biostudies-literature