scholarly journals Transcriptional control of ribosome production in regenerating rat liver

1982 ◽  
Vol 208 (1) ◽  
pp. 101-108 ◽  
Author(s):  
M D Dabeva ◽  
K P Dudov
Keyword(s):  
Rat Liver ◽  
Transcriptional Control ◽  
18S Rrna ◽  
Specific Radioactivity ◽  
Rrna Synthesis ◽  
Transcriptional Level ◽  
Enhanced Production ◽  
Regenerating Rat Liver ◽  
Fold Stimulation

Kinetic experiments of labelling in vivo with [14C]orotate of cellular free UMP and/or UTP, nucleolar, nucleoplasmic and cytoplasmic rRNA in normal and 12 h-regenerating rat liver were performed. The specific-radioactivity curves obtained were analysed by computer and the rates of synthesis of precursor rRNA (45S pre-rRNA) and cytoplasmic 28S and 18S rRNA calculated. (a) The rates of synthesis of 45S pre-rRNA in normal and regenerating rat liver are 1400 and 3700 molecules/min per nucleus respectively; (b) the average rates of formation of mature 28S and 18S rRNA are identical with the rates of synthesis of 45S pre-rRNA in both normal and regenerating rat liver. Thus the synthesis of rRNA in 12h-regenerating rat liver is activated 2.7-fold. The analysis of rRNA synthesis in isolated nucleoli also shows a 2.7-fold stimulation of transcription in regenerating liver. It is concluded that all the 45S pre-rRNA molecules synthesized are processed and transferred as 28S and 18S rRNA in the cytoplasm, i.e. degradation (wastage) of newly synthesized ribosomes in the nucleus does not occur in both normal and regenerating rat liver. Thus the enhanced production of ribosomes in regenerating rat liver is regulated only at the transcriptional level.

DEOXYCYTIDYLATE DEAMINASE LEVELS IN REGENERATING RAT LIVER

1961 ◽  
Vol 39 (6) ◽  
pp. 1043-1054 ◽  
Author(s):  
D. K. Myers ◽  
C. Anne Hemphill ◽  
Constance M. Townsend
Keyword(s):  
Dna Synthesis ◽  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Deoxyribonucleic Acid ◽  
Regenerating Liver ◽  
Regenerating Rat Liver ◽  
High Level ◽  
Early Regeneration

Deoxycytidylate deaminase activity and net synthesis of deoxyribonucleic acid (DNA) in vivo were found to increase at approximately the same time during the early stages of liver regeneration. However, deaminase activity in the regenerating liver remained at a high level for 1 day after DNA synthesis had slowed down again during the later stages of regeneration. The increase in deaminase activity was restricted as a result of exposure to 600 r X radiation during early regeneration, but this effect only became evident 11–16 hours after the irradiation. Irradiation on the second day after partial hepatectomy, when deaminase levels in control regenerating livers were relatively constant, failed to affect the deaminase activity immediately but did produce a 40–50% decrease in activity 11–16 hours later. Other antimitotic agents, e.g., colchicine, had little effect on deaminase activity.

scholarly journals The availability of inorganic sulphate in blood for sulphate conjugation of drugs in rat liver in vivo. (35S)Sulphate incorporation into harmol sulphate

1978 ◽  
Vol 172 (2) ◽  
pp. 247-251 ◽  
Author(s):  
G J Mulder ◽  
E Scholtens
Keyword(s):  
Plasma Concentration ◽  
Rat Liver ◽  
Biliary Excretion ◽  
Time Course ◽  
Specific Radioactivity ◽  
Pool Size ◽  
Inorganic Sulphate ◽  
Initial Decrease ◽  
Sulphate Conjugate

1. When Na235SO4 is injected intravenously in rats, it is immediately available for sulphate conjugation of the phenolic drug harmol (7-hydroxyl-1-methyl-9H-pyrido[3,4-b]indole) in the liver. This was established by following the time course of the biliary excretion of the sulphate conjugate of harmol, and the incorporation of [35S]sulphate into harmol sulphate. 2. During the 10min immediately after injection of Na235SO4 re-distribution of [35S]sulphate took place, which resulted in a rapid initial decrease in the plasma concentration of [35S]sulphate; a concomitant decrease in the amount of [35S]sulphate incorporated into harmol sulphate was observed, indicating that the co-substrate of sulphation, adenosine 3′-phosphate 5′-sulphatophosphate, equilibrates rapidly with [35S]sulphate in plasma. 3. The results suggest that the pool size of adenosine 3′-phosphate 5′-sulphatophosphate is very small; therefore the specific radioactivity of [35S]sulphate in plasma determines the specific radioactivity incorporated into sulphate esters at any time.

scholarly journals Post-transcriptional regulation of ribosome formation in the nucleus of regenerating rat liver

1983 ◽  
Vol 210 (1) ◽  
pp. 183-192 ◽  
Author(s):  
K P Dudov ◽  
M D Dabeva
Keyword(s):  
Rat Liver ◽  
Ribosome Biogenesis ◽  
Rrna Processing ◽  
Regenerating Liver ◽  
Regenerating Rat Liver ◽  
Rrna Species ◽  
Rrna Maturation ◽  
The Individual ◽  
Post Transcriptional Regulation

Kinetic experiments on RNA labelling in vivo with [14C]orotate were performed with normal and 12h-regenerating rat liver. The specific radioactivities of nucleolar, nucleoplasmic and cytoplasmic rRNA species were analysed by computer according to the models of rRNA processing and nucleo-cytoplasmic migration given previously [Dudov, Dabeva, Hadjiolov & Todorov, Biochem. J. (1978) 171, 375-383]. The rates of formation and the half-lives of the individual pre-rRNA and rRNA species were determined in both normal and regenerating liver. The results show clearly that the formation of ribosomes in regenerating rat liver is post-transcriptionally activated: (a) the half-lives of all the nucleolar pre-rRNA and rRNA species are decreased by 30% on average; (b) the pre-rRNA processing is directed through the shortest maturation pathway: 45 S leads to 32 S + 18 S leads to 28 S; (c) the nucleo-cytoplasmic transfer of ribosomes is accelerated. As a consequence, the time for formation and appearance of ribosomes in the cytoplasm is shortened 1.5-fold for the large and 2-fold for the small subparticle. A new scheme for endonuclease cleavage of 45 S pre-rRNA is proposed, which explains the alterations in pre-rRNA processing in regenerating liver. Its validity for pre-rRNA processing in other eukaryotes is discussed. It is concluded that: (i) the control sites in the intranucleolar formation of 28 S and 18 S rRNA are the immediate precursor of 28 S rRNA, 32 S pre-rRNA, and the primary pre-rRNA, 45 S pre-rRNA, respectively; (ii) the limiting step in the post-transcriptional stages of ribosome biogenesis is the pre-rRNA maturation.

Inhibition of in vivo DNA synthesis in regenerating rat liver following thermal injury

1989 ◽  
Vol 160 (1) ◽  
pp. 196-201 ◽  
Author(s):  
Edward A. Carter ◽  
Sara E. Kirkham ◽  
Ronald G. Tompkins ◽  
John F. Burke
Keyword(s):  
Dna Synthesis ◽  
Rat Liver ◽  
Thermal Injury ◽  
Regenerating Rat Liver

Incorporation in vivo of [32P]orthophosphate and [Me-3H]choline into rough microsomal, Golgi, and plasma membranes of rat liver

1977 ◽  
Vol 55 (8) ◽  
pp. 876-885 ◽  
Author(s):  
Patricia L. Chang ◽  
John R. Riordan ◽  
Mario A. Moscarello ◽  
Jennifer M. Sturgess
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Rat Liver ◽  
Plasma Membranes ◽  
Specific Activity ◽  
Specific Radioactivity ◽  
Marker Enzyme ◽  
Golgi Membranes ◽  
Endomembrane Flow

To study membrane biogenesis and to test the validity of the endomembrane flow hypothesis, incorporation of 32P and [Me-3H]choline in vivo into membranes of the rat liver was followed. Rough microsomal, Golgi-rich, and plasma membrane fractions were monitored with marker enzyme assays and shown with morphometric analysis to contain 82% rough microsomes, at least 70% Golgi complexes, and 88% plasma membranes, respectively. Membrane subfractions from the rough microsomal and Golgi-rich fractions were prepared by sonic disruption.At 5 to 30 min after 32P injection, the specific radioactivity of phosphatidylcholine was higher in the rough microsomal membranes than in the Golgi membranes. From 1 to 3 h, the specific activity of phosphatidylcholine in Golgi membranes became higher and reached the maximum at about 3 h. Although the plasma membrane had the lowest specific radioactivity throughout 0.25–3 h, it increased rapidly thereafter to attain the highest specific activity at 5 h. Both rough microsomal and plasma membranes reached their maxima at 5 h.The specific radioactivity of [32P]phosphatidylethanolamine in the three membrane fractions was similar to that of [32P]phosphatidylcholine except from 5 to 30 min, when the specific radioactivity of phosphatidylethanolamine in the Golgi membranes was similar to the rough microsomal membranes.At 15 min to 5 h after [Me-3H]choline injection, more than 90% of the radioactivity in all the membranes was acid-precipitable. The specific radioactivities of the acid-precipitated membranes, expressed as dpm per milligram protein, reached the maximum at 3 h. After [Me-3H]choline injection, the specific radioactivity of phosphatidylcholine separated from the lipid extract of the acid-precipitated membranes (dpm per micromole phosphorus) did not differ significantly in the three membrane fractions. The results indicated rapid incorporation of choline into membrane phosphatidylcholine by the rough endoplasmic reticulum, Golgi, and plasma membranes simultaneously.The data with both 32P and [Me-3H]choline precursors did not support the endomembrane flow hypothesis. The Golgi complexes apparently synthesized phosphatidylethanolamine and incorporated choline into phosphatidylcholine as well as the endoplasmic reticulum. The results are discussed with relevance to current hypotheses on the biogenesis and transfer of membrane phospholipids.

scholarly journals Measurement of protein turnover in rat liver. Analysis of the complex curve for decay of label in a mixture of proteins

1976 ◽  
Vol 156 (3) ◽  
pp. 657-663 ◽  
Author(s):  
P J Garlick ◽  
J C Waterlow ◽  
R W Swick
Keyword(s):  
Rat Liver ◽  
Turnover Rate ◽  
Decay Curve ◽  
Specific Radioactivity ◽  
Liver Protein ◽  
Turnover Rates ◽  
A Value ◽  
Maximum Value ◽  
Single Exponential

The curve for decay of 14C in rat liver protein labelled by injection of NaH14CO3 was analysed to obtain the average turnover rate of mixed liver protein. Three different methods of analysis were used. (1) Unlike decay curves from homogeneous proteins, the curve did not fit a single exponential, but a good fit was obtained with three exponentials. By assuming that the mixture contained three major components with different turnover rates, the calculated value for the average turnover rate (k) was close to 40% per day. (2) k was also calculated from the area under the decay curve, a method which makes no assumptions about the number of proteins in the mixture. This method also gave a value close to 40% per day. (3) It was shown empirically, both by simulation of decay of label in model mixtures of protein and with the decay curve measured in vivo, that k can be calculated from the time taken for the specific radioactivity to fall to 10% of its maximum value. This is an advantage, since the other two methods require the decay curve to be measured over a much longer period of time.

scholarly journals Thymidine metabolism in regenerating rat liver one to two hours after partial hepatectomy

1973 ◽  
Vol 136 (3) ◽  
pp. 571-577 ◽  
Author(s):  
Margery G. Ord ◽  
Lloyd A. Stocken
Keyword(s):  
Partial Hepatectomy ◽  
Intravenous Injection ◽  
Rat Liver ◽  
Thymidine Uptake ◽  
Regenerating Rat Liver ◽  
Perfusion Studies ◽  
Saturation Kinetics

1. When [3H]thymidine was injected intravenously into rats in amounts up to 40mg/kg body wt. and the3H radioactivity in the livers measured at 30min, saturation kinetics for thymidine uptake were not found. If the animals were examined 3 min after intravenous injection, saturation could be attained in normal rats with 12mg of thymidine/kg and in partially hepatectomized rats with 4mg/kg. At concentrations of thymidine close to saturation, no differences were found in rate or amount of uptake/g of liver between normal and partially hepatectomized rats 1–2h after operation. 2. Perfusion techniques were used to compare thymidine uptakes in the two sets of rats at concentrations up to 40μm-thymidine. Uptakes with tracer amounts of thymidine after 30min were identical in vivo and in the perfusion studies and were twice as great in livers from partially hepatectomized rats with concentrations up to 40μm-thymidine. 3. At 1.5h after operation there was nearly twice as much β-aminoisobutyrate present per g of liver from partially hepatectomized as compared with normal rats.

scholarly journals Intranuclear maturation pathways of rat liver ribosomal ribonucleic acids

1976 ◽  
Vol 160 (3) ◽  
pp. 495-503 ◽  
Author(s):  
M D Dabeva ◽  
K P Dudov ◽  
A A Hadjiolov ◽  
I Emanuilov ◽  
B N Todorov
Keyword(s):  
Secondary Structure ◽  
Rat Liver ◽  
Mammalian Cells ◽  
18S Rrna ◽  
Electron Microscopic Observation ◽  
28S Rrna ◽  
Electron Microscopic ◽  
Rrna Species ◽  
A Minor

The maturation of pre-rRNA (precursor to rRNA)in liver nuclei is studied by agar/ureagel electrophoresis, kinetics of labelling in vivo with [14C] orotate and electron-microscopic observation of secondary structure of RNA molecules. (1) Processing starts from primary pre-rRNA molecules with average mol. wt. 4.6×10(6)(45S) containing the segments of both 28S and 18S rRNA. These molecules form a heterogeneous peak on electrophoresis. The 28S rRNA segment is homogeneous in its secondary structure. However, the large transcribed spacer segment (presumably at the 5′-end) is heterogeneous in size and secondary structure. A minor early labelled RNA component with mol.wt. about 5.8×10(6) is reproducibly found, but its role as a pre-rRNA species remains to be determined. (2) The following intermediate pre-rRNA species are identified: 3.25×10(6) mol.wt.(41S), a precursor common to both mature rRNA species; 2.60×10(6)(36S) and 2.15×10(6)(32S) precursors to 28S rRNA; 1.05×10(6) (21S) precursor to 18S rRNA. The pre-rRNA molecules in rat liver are identical in size and secondary structure with those observed in other mammalian cells. These results suggest that the endonuclease-cleavage sites along the pre-rRNA chain are identical in all mammalian cells. (3) Labelling kinetics and the simultaneous existence of both 36S and 21S pre-rRNA reveal that processing of primary pre-rRNA in adult rat liver occurs simultaneously by at least two major pathways: (i) 45S → 41S → 32S+21S → 28S+18S rRNA and (ii) 45S → 41S → 36S+18S → 32S → 28S rRNA. The two pathways differ by the temporal sequence of endonuclease attack along the 41 S pre-rRNA chain. A minor fraction (mol.wt.2.9×10(6), 39S) is identified as most likely originating by a direct split of 28S rRNA from 45S pre-rRNA. These results show that in liver considerable flexibility exists in the order of cleavage of pre-rRNA molecules during processing.

Alterations in Deoxyribonucleic Acid from Regenerating Rat Liver after X-radiation in vivo

Nature ◽  
1962 ◽  
Vol 194 (4831) ◽  
pp. 883-884 ◽  
Author(s):  
R. FOSTER ◽  
MARGERY G. ORD
Keyword(s):  
Rat Liver ◽  
Deoxyribonucleic Acid ◽  
Regenerating Rat Liver
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