scholarly journals Biosynthesis of phosphatidylethanolamines and phosphatidylcholines from ethanolamine and choline in rat liver

1975 ◽  
Vol 146 (2) ◽  
pp. 309-315 ◽  
Author(s):  
R Sundler ◽  
B Akesson
Keyword(s):  
Rat Liver ◽  
Molecular Species ◽  
Kinetic Models ◽  
Quantitative Data ◽  
Specific Radioactivity ◽  
Similar Rate ◽  
Time Intervals ◽  
Previous Suggestion ◽  
Kinetics Of

1. The kinetics of phosphatidylcholine and phosphatidylethanolamine synthesis in rat liver were followed 5-60 min after the intraportal injection of [14-C]choline and [3-H]-ethanolamine. 2. At all time-intervals the specific radioactivity of CDP-choline was only about half that of phosphorylcholine. This indicated that CDP-choline was formed at a similar rate from phosphorylcholine and phosphatidylcholines, the latter probably through the reverse reaction of cholinephosphotransferase (EC 2.7.8.2.). In view of recent data obtained from experiments in vitro this implies a significant role for the cholinephosphotransferase reaction in the turnover of molecular species of phosphatidylcholine. 3. The specific radioactivity of CDP-ethanolamine was about twice that of phosphorylethanolamine at all time-intervals studied. This supports a previous suggestion that the liver phosphorylethanolamine pool is subject to compartmentation and shows that there is no rapid equilibration between different pools. In contrast with a recent study, no evidence was found for any significant methylation of phosphoryl-or CDP-ethanolamine to the corresponding choline derivative. 4. Quantitative data on the biosynthesis of molecular species of phosphoLIPIDS via CDP derivatives were calculated according to simple kinetic models. They were in the same range as those calculated from earlier data on precusors incorporated via diacylglycerols. 5. The proportion of radioactive phosphatidylethanolamines appearing in the plasma was approximately ten times lower than that for phosphatidylcholines. No selectivity was observed in the transfer into plasma of different molecular species of phosphatidylethanolamine.

Studies on the Biosynthesis of Flavin Nucleotides from 2-14C-Riboflavin by Rat Liver and Kidney

1973 ◽  
Vol 51 (6) ◽  
pp. 772-782 ◽  
Author(s):  
A. G. Fazekas ◽  
T. Sandor
Keyword(s):  
Rat Liver ◽  
Flavin Adenine Dinucleotide ◽  
Total Radioactivity ◽  
Flavin Mononucleotide ◽  
Time Intervals ◽  
Adult Rats ◽  
Liver And Kidney ◽  
Rat Liver Cytosol

2-14C-Riboflavin was injected subcutaneously into young adult rats to study the biosynthesis of flavin mononucleotide (FMN) and flavin–adenine dinucleotide (FAD) in the liver and kidneys. Animals were sacrificed at different time intervals following the administration of labelled riboflavin (RF), and radioactive flavins were determined in their tissues by a newly devised method. Both tissues accumulated radioactive riboflavin rapidly and peak levels were obtained at 90 min after the injection, when over 80% of the total radioactivity of the liver was present in FAD. At this time the liver contained 17% of the injected dose of 2-14C-RF. The kidneys contained relatively high quantities of free RF due to the concentration and urinary excretion of the vitamin.Analysis of subcellular fractions of the liver of animals injected with 2-14C-RF revealed that most of the radioactivity was present in mitochondria and nuclei. The flavin nucleotides of rat liver cytosol became progressively associated with macromolecules in vivo. However, there was no significant binding of free RF by macromolecules in blood plasma or liver cytosol.Kinetic studies and incubations with liver slices indicated that RF freely diffuses into the liver cells, is rapidly converted into FAD, and becomes attached to apoenzymes. The tissue uptake of RF and FMN formation is considerably influenced by the concentration of RF present in the system, both in vivo and in vitro.

Kinetics of in vitro nitro reduction of 2,4-dinitrophenol by rat liver homogenates

1974 ◽  
Vol 27 (1) ◽  
pp. 140-144 ◽  
Author(s):  
Julie L. Eiseman ◽  
Perry J. Gehring ◽  
James E. Gibson
Keyword(s):  
Rat Liver ◽  
Liver Homogenates ◽  
Kinetics Of ◽  
Nitro Reduction

Measurements of the rate of production of bacteria in the rumen of buffalo calves

1974 ◽  
Vol 83 (1) ◽  
pp. 13-17 ◽  
Author(s):  
U. B. Singh ◽  
D. N. Verma ◽  
A. Varma ◽  
S. K. Ranjhan
Keyword(s):  
Specific Radioactivity ◽  
Turnover Time ◽  
Sodium Sulphate ◽  
Bacterial Cells ◽  
Buffalo Calves ◽  
Time Intervals ◽  
Turn Over ◽  
Specific Radio

SUMMARYA technique is described for thein vivoestimation of the rate of production of bacteria in the rumen of buffalo calves. The animals were given their daily ration in 12 equal amounts at 2-h intervals. The bacterial cells from the rumen were labelled either with14C or36S byin vitroincubation in the presence of [U-14C]DL-leucine or35S-sodium sulphate. Labelled bacterial cells were injected in a single dose into the rumen. Samples of the ruminal fluid were drawn at various time intervals for 9 h and the specific radio-activity of the bacteria determined. The dilution in the specific radioactivity was used to calculate the turn-over time and rates of production of bacteria in the rumen. The average turnover time was 308 min. The production rate of bacteria averaged 211 mg/min (20·3 g/mole VFA produced).

scholarly journals The catabolism of cholesterol in vitro. Formation of 3α,7α,12α-trihydroxy-5β-cholestanoic acid from cholesterol by rat liver

1969 ◽  
Vol 114 (1) ◽  
pp. 1-3 ◽  
Author(s):  
D. Mendelsohn ◽  
L. Mendelsohn
Keyword(s):  
Gall Bladder ◽  
Bile Acids ◽  
Rat Liver ◽  
Specific Radioactivity ◽  
Liver Preparation

1. Both 25-d- and 25-l-3α,7α,12α-trihydroxy-5β-cholestanoic acid were isolated from the gall-bladder bile of Crocodylus niloticus. 2. The catabolism of cholesterol to 25-d- and 25-l-3α,7α,12α-trihydroxy-5β-cholestanoic acid respectively was studied by using a rat liver preparation in vitro. The results show that rat liver can metabolize cholesterol to both forms of 3α,7α,12α-trihydroxy-5β-cholestanoic acid. However, a preference was noted for the formation from [4−14C]cholesterol of 3α,7α,12α-trihydroxy-5β-cholestanoic acid (25-d), which was isolated from the incubations with a specific radioactivity about four times that of 3α,7α,12α-trihydroxy-5β-cholestanoic acid (25-l). 3. The results indicate that 3α,7α,12α-trihydroxy-5β-cholestanoic acid is a normal intermediate in the biosynthesis of bile acids from cholesterol in the rat.

Mass spectroscopic analysis of phosphatidylinositol synthesis using 6-deuteriated-myo-inositol: comparison of the molecular specificities and acyl remodelling mechanisms in mouse tissues and cultured cells

2004 ◽  
Vol 32 (6) ◽  
pp. 1057-1059 ◽  
Author(s):  
A.D. Postle ◽  
H. Dombrowsky ◽  
H. Clarke ◽  
C.J. Pynn ◽  
G. Koster ◽  
...  
Keyword(s):  
Molecular Species ◽  
Cultured Cells ◽  
Ionization Mass ◽  
Membrane Composition ◽  
Mouse Tissues ◽  
Wide Range ◽  
Kinetics Of ◽  
Hydrolysis Of

Mammalian cell PtdIns (phosphatidylinositol) in vivo is enriched in the sn-1-stearoyl 2-arachidonoyl species, the physiological precursor of phosphatidylinositol 4,5-bisphosphate. Mechanisms regulating this specificity are unclear but are typically lost for cells in culture. We used ESI-MS (tandem electrospray ionization-mass spectrometry) to determine the molecular species of PtdIns synthesized by mouse tissues in vivo compared with cultured cells in vitro. After incorporation of deuteriated myo-d6-inositol over 3 h, endogenous and newly synthesized PtdIns and lysoPtdIns species were quantified from precursor scans of m/z 241− and m/z 247− respectively. PtdIns was synthesized as a wide range of species irrespective of the final membrane composition. Analyses of isotope enrichments argued against acyl remodelling as the major regulatory mechanism: composition of the lysoPtdIns pool under all conditions reflected that of either endogenous or newly synthesized PtdIns and was always at equilibrium. The kinetics of PtdIns synthesis, together with the prolonged time scale required for achieving final equilibrium compositions suggest that selective transport between membranes and/or hydrolysis of selected molecular species are the most probable mechanisms regulating compositions of PtdIns and, ultimately, phosphatidylinositol 4,5-bisphosphate.

scholarly journals The submicrosomal localization of acyl-coenzyme A–cholesterol acyltransferase and its substrate, and of cholesteryl esters in rat liver

1978 ◽  
Vol 174 (3) ◽  
pp. 863-872 ◽  
Author(s):  
Santhirasegaram Balasubramaniam ◽  
Soundararajan Venkatesan ◽  
Konstantinos A. Mitropoulos ◽  
Timothy J. Peters
Keyword(s):  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
Plasma Membranes ◽  
Microsomal Fraction ◽  
Smooth Endoplasmic Reticulum ◽  
Cholesterol Acyltransferase ◽  
Specific Radioactivity ◽  
Cholesteryl Esters ◽  
Distribution Profile

To determine the submicrosomal distribution of acyl-CoA–cholesterol acyltransferase and of cholesteryl esters, the microsomal fraction and the digitonin-treated microsomal preparation of rat liver were subjected to analytical centrifugation on sucrose density gradients. With untreated microsomal fractions the distribution profile and the median density of acyl-CoA–cholesterol acyltransferase were very similar to those of RNA. This is in contrast with hydroxymethylglutaryl-CoA reductase and cholesterol 7α-hydroxylase, which are confined to endoplasmic reticulum membranes with low ribosomal coating. In digitonin-treated microsomal preparations activity of acyl-CoA–cholesterol acyltransferase was not detectable. The labelling of untreated microsomal fractions with trace amounts of [14C]cholesterol followed by subfractionation of the labelled microsomal fraction showed that the specific radioactivity of cholesteryl esters obtained in vitro by the various subfractions was similar with all subfractions but different from the specific radioactivity of the 7α-hydroxycholesterol obtained in vitro by the same subfraction. These results demonstrate the existence of two pools of cholesterol confined to membranes from the endoplasmic reticulum, one acting as substrate for cholesterol 7α-hydroxylase and the other acting as substrate for acyl-CoA–cholesterol acyltransferase. The major part of cholesteryl esters present in both untreated and digitonin-treated microsomal fractions was distributed at densities similar to those of membranes from the smooth endoplasmic reticulum and at densities lower than those of smooth membranes from Golgi apparatus. The ratio of the concentrations of non-esterified to esterified cholesterol in the subfractions from both untreated and digitonin-treated microsomal fractions was highest at the maximum distribution of plasma membranes.

Interrelationships in the Metabolism of Liver Arachidonoyllecithins and Plasma Cholesteryl Arachidonate in the Rat

1971 ◽  
Vol 49 (9) ◽  
pp. 1005-1011 ◽  
Author(s):  
B. J. Holub ◽  
A. Kuksis
Keyword(s):  
Arachidonic Acid ◽  
Rat Liver ◽  
Molecular Species ◽  
Free Cholesterol ◽  
Plasma Lipids ◽  
Male Rats ◽  
Gradual Release ◽  
Acid Esters ◽  
Net Transfer

Male rats were injected intravenously with albumin-bound 1-14C-arachidonic acid or 1-14C-palmitoyllysolecithin and the molecular species of the labeled liver and plasma lipids were identified after various periods of time. There was an extensive esterification of lysolecithin with arachidonic acid in the rat liver, which was in agreement with the earlier demonstrated specific incorporation of labeled arachidonic acid into the liver lysolecithins. The subsequent gradual release of the labeled liver arachidonoyllecithins into the plasma was accompanied by a steady rise in the radioactivity of plasma cholesteryl arachidonate. In other experiments, it was shown that radioactive arachidonic acid esters of cholesterol are readily formed in vitro from 1-14C-arachidonoyllecithin and free cholesterol, and that such esters upon subsequent injection can contribute arachidonic acid for the biogenesis of lecithin from lysolecithin in the liver as a result of hydrolysis. These results are compatible with the operation of a plasma–liver cycle which results in a net transfer of cholesterol from plasma to the liver and a return of lysolecithin and arachidonic acid to the plasma in the form of lecithin.

Utilization of fatty acids by rat liver slices as a function of medium concentration

1964 ◽  
Vol 206 (2) ◽  
pp. 345-350 ◽  
Author(s):  
Herbert Rose ◽  
Martha Vaughan ◽  
Daniel Steinberg
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Rat Liver ◽  
Neutral Lipids ◽  
Specific Radioactivity ◽  
Lipid Synthesis ◽  
Normal Liver ◽  
Precursor Pool ◽  
Liver Slices

The rate of incorporation of palmitate-1-C14 into neutral lipids and phospholipids of rat liver slices in vitro and its conversion to C14O2 were shown to increase markedly as the free fatty acid (FFA) concentration of the medium was increased. Incorporation into lipids and conversion to C14O2 proceeded linearly with time over 60 min. The incorporation of glycerol-1,3-C14 into neutral lipids also increased as the FFA concentration of the medium was increased but incorporation into phospholipids was unchanged. It is concluded that high FFA concentrations cause a true increase in rate of neutral lipid synthesis by liver slices. The associated increase in incorporation of labeled palmitate into phospholipids most likely reflects the higher specific radioactivity of the precursor pool of FFA and/or an exchange reaction rather than a true increase in net synthesis. A method for recovering tissue FFA quantitatively is described. Normal liver was found to contain 0.40–0.87 µEq FFA/g wet wt. The composition of this tissue FFA fraction is presented.

Thyroxine transport from blood to brain via transthyretin synthesis in choroid plexus

1990 ◽  
Vol 258 (2) ◽  
pp. R338-R345 ◽  
Author(s):  
G. Schreiber ◽  
A. R. Aldred ◽  
A. Jaworowski ◽  
C. Nilsson ◽  
M. G. Achen ◽  
...  
Keyword(s):  
Cerebrospinal Fluid ◽  
Thyroid Hormones ◽  
Choroid Plexus ◽  
Intravenous Injection ◽  
Rat Liver ◽  
Specific Radioactivity ◽  
Perfusion Medium ◽  
The Brain

The transport of thyroxine from the bloodstream to the brain and the synthesis and secretion of transthyretin (formerly called prealbumin) were studied in rats and in sheep choroid plexus perfused in vitro. Rat choroid plexus contained 4.4 micrograms and rat liver 0.39 micrograms transthyretin mRNA per gram wet tissue. The specific radioactivity of transthyretin isolated from cerebrospinal fluid of rats 60 min after intravenous injection of [14C]leucine was greater than 50 times that of transthyretin from serum. After adding [14C]leucine to the perfusion medium of an in vitro perfused sheep choroid plexus, highly radioactive transthyretin was isolated from freshly secreted cerebrospinal fluid collected from the exposed choroid plexus surface. Secretion of newly synthesized transthyretin into the perfusion medium could not be demonstrated. After intravenous injection of [125I]-thyroxine into rats, a maximum in the curve of radioactivity in tissue plotted against time after injection was observed first for choroid plexus, thereafter for cerebrospinal fluid, and still later for cortex and striatum. Based on the obtained data, a hypothesis is derived for the mechanism of the transport of thyroid hormones from the bloodstream to the brain involving transthyretin synthesized in choroid plexus and secreted into the cerebrospinal fluid.

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