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At least 19 recordsLinked to original sources
PubMed1976

The incorporation of radioactive fatty acids and of radioactive derivatives of glucose into the phospholipids of subsynaptosomal fractions of cerebral cortex.

1. Crude synaptosomal fractions (P2) from guinea-pig cerebral cortex were incubated in a Krebs-glucose medium containing labelled fatty acids and [3H]glucose. After the shortest incubation period (7.5 min) a high percentage (50-80%) of the total radioactive fatty acids was found in the P2 fractions. 2. After the incubation, the synaptosomal fractions were submitted to hypo-osmotic disruption and subsynaptosomal fractionation was carried out by using discontinuous-sucrose-gradient centrifugation. The specific radioactivities of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol were determined in fractions D (synaptic vesicles), E (microsomal preparation) and H (disrupted synaptosomes), as were the specific activities of a number of marker enzymes and the distribution of acetylcholine. 3. By using [14C]oleate, [14C]arachidonate, [3H]palmitate and [3H]glucose, the order to specific radioactivities in fraction D was found to be: phosphatidylinositol greater than phosphatidylcholine greater than phosphatidylserine greater than phosphatidylethanolamine. 4. The specific radioactivities of phosphatidylcholine and phosphatidylethanolamine were always higher in fraction D than in fraction E. As fraction E had higher specific activities of several membrane marker enzymes, the enhanced labelling found in fraction D was considered to be localized in the synaptic vesicles. In this fraction, phosphatidylinositol made particularly large contributions to the total phospholipid labelling derived from [14C]arachidonate and [3H]glucose. 5. The similar labelling ratios of fatty acid/glucose in the phospholipids of fractions D and E, and the high specific radioactivities in the total phospholipid of the soluble fraction O, suggested intrasynaptosomal phospholipid transport.

Acetylcholine↗
PubMed1980

Temperature-mediated hyperinduction of fatty acid desaturation in pre-existing and newly formed fatty acids synthesized endogenously in Bacillus megaterium.

3H-labedeled fatty acids synthesized endogenously by Bacillus megaterium ATCC 14581 growing at 35 degrees C in the presence of L-[G-3H]valine exhibited the same time-course of hyperinduced desaturation following a temperature decrease to 20 degrees C as was observed previously with exogenously supplied 14C-labeled fatty acids. Radioactive fatty acids synthesized in the presence of [U-14C]glucose during hyperinduction at 20 degrees C following a shift-down from 35 degrees C were desaturated at the same relative rate as 14C-labeled fatty acids synthesized previously at 35 degrees C, suggesting that the newly synthesized fatty acids equilibrate with a large portion of the preexisting moieties before becoming susceptible to desaturation.

Bacillus megaterium↗
PubMed1980

The incorporation of radioactive fatty acids into the phospholipids of nerve-cell-body membranes in vivo.

1. Nerve cell bodies were isolated in bulk from cerebral cortices of 15 day-old rabbits after intrathecal injections of [(3)H]plamitate, [(3)H]oleate or [(3)H]arachidonate and [(14)C]glycerol. 2. Nuclear, microsomal and two mitochondrial fractions were isolated from homogenates of the radioactively labelled nerve cell bodies by using differential and discontinuous-gradient centrifugation. 3. After 7.5min in vivo, a high percentage (>80%) of the total (3)H-labelled fatty acid radioactivity was found in the membrane fractions of the nerve cell bodies, whereas after 60min in vivo 50% of the total [(14)C]glycerol radioactivity was found in the high-speed supernatant. 4. The specific radioactivities of phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, and the radioactivity in neutral lipid and non-esterified fatty acid fractions were determined in the four subfractions, as were the distributions of several marker enzymes and nucleates. 5. With respect of (3)H-labelled fatty acid, the phospholipids of the nuclear fraction had the highest specific radioactivities of the four subfractions. However, for [(14)C]glycerol labelling, generally the (14)C specific radioactivities for individual phospholipids were comparable in the four subfractions. This latter observation suggests transport of phospholipids synthesized de novo between membranes of the nerve cell body. 6. Double-labelling experiments demonstrated that individual phospholipids and the combined neutral lipids of the nuclear fraction had higher labelling ratios of (3)H-labelled fatty acid/[(14)C]glycerol than did the corresponding lipids of the microsomal or mitochondrial fractions. 7. On the basis of the labelling results and the marker studies, it is proposed that it is indeed the nuclei of the nuclear fraction that have these lipids highly labelled with (3)H-labelled fatty acid, and the existence of nuclear acyl transferases that are responsible for this fatty acid incorporation is suggested.

Animals↗
PubMed1989

Galactolipids of Thylakoid Pigment Protein Complexes Separated Electrophoretically from Thylakoids of Dunaliella salina Labeled with Radioactive Fatty Acids.

Experiments have been conducted to determine whether mono- and digalactosyldiacylglycerols (MGDG and DGDG) labeled by short term exposure of the green alga Dunaliella salina to exogenous radioactive lauric, myristic, or palmitic acids are preferentially recovered in one or more thylakoid protein complexes separated by electrophoresis on nondenaturing gels. A selective retention of certain lipid classes and molecular species by the major electrophoretically separable fractions, oligomeric form (LHCP-1) and monomeric form (LHCP-3) of hight-harvesting chlorophyll a/b protein complex, and major photosystem I protein complex (CPla), and nonprotein-bound lipids, was indicated. After 5 min of labeling with (3)H-palmitate the specific radioactivities of MGDG and DGDG molecular species recovered from LHCP-3 and CPla were slightly higher and lower, respectively, than specific radioactivities of equivalent molecular species from LHCP-1 and nonprotein-bound lipid. However, the differences were smaller than those which have been observed between whole thylakoids and the more highly labeled chloroplast envelopes from briefly labeled cells.

Journal Article↗
PubMed1983

The rapid incorporation of radioactive fatty acid into triacylglycerols during the in vitro acylation of native lipids of neuronal nuclei.

Using neuronal nuclei (N1) and microsomes (P3) isolated from cerebral cortices of 15-day-old rabbits, the incorporation of [14C]oleate was followed in vitro, making use of fatty acid activation factors and endogenous membrane acyl acceptors. Of the lipids of N1, it was triacylglycerol which showed the highest rates of labelling and which represented 71-80% of the total incorporated radioactivity in this fraction. Specific rates of N1 triacylglycerol formation were 63-166 times those of P3 triacylglycerols (based upon membrane phospholipid content). In P3, phospholipids made up 85% of the total microsomal lipid labelling. The incorporation of oleate was dependent upon ATP and coenzyme A, and acyl-CoA synthetase activities were demonstrated in N1 and P3 (specific activity ratio, N1:P3 = 4.5). Using exogenous [14C]oleoyl-CoA, high rates of N1 triacylglycerol labelling were still seen relative to P3, but rates of diacylglycerol and phospholipid labelling were substantially elevated in both fractions in contrast to rates found using [14C]oleate. By increasing levels of endogenous diacylglycerol using preincubations with phospholipase C, a 3-fold increase was seen in specific rates of triacylglycerol formation in both fractions in subsequent assays with [14C]oleate. A 4.5-fold increase in N1 diacylglycerol concentrations was found when N1 was incubated for 10 min in the absence of fatty acid, ATP and coenzyme A. It is concluded that neuronal nuclei have a very active diacylglycerol acyltransferase as well as the ability to generate diacylglycerol substrates.

Acylation↗
PubMed1976

Effects of glycerol on VLDL secretion by the isolated rat liver.

Stimulation of VLDL production by increasing fatty acid availability is now well established. However, a possible regulatory role of glycerol, another lipid precursor, in VLDL synthesis by the liver has not yet been substaniated. The present experiments investigate this problem using the isolated perfused rat liver. [14C] Glycerol uptake and metabolism were studied at two different glycerol concentrations: 1 mumol/perfusate (control) or 1.6 mmol/perfusate. VLDL production and lipid synthesis were investigated using [14C]leucine and several labelled fatty acids as precursors in control and glycerol-overloaded livers. Neoglycogenesis and lipogenesis from glycerol carbons are negligible in our conditions. The absolute amount of glycerol, but not the precentage, taken up by the liver, increased after raising its concentration in the perfusate. A major part of exogenous (plasmatic) glycerol was esterified with endogenous (non plasmatic) fatty acids. Incorporation of radioactive fatty acids into liver or plasma lipids was lower than in the the control group. Significant differences were observed between saturated and unsaturated fatty acids used as lipid precursors. Production of VLDL as assessed by radioactive leucine and fatty acid incorporation in the VLDL of the perfusate was depressed by glycerol. Glycerol partly inhibits the normal stimulation of VLDL production by plasmatic fatty acid overload.

Animals↗
PubMed1982

Synthesis and biosynthetic utilization of radioactive photoreactive fatty acids.

A synthesis of a homologous series of highly radioactive photoreactive fatty acids has been developed. Oxidative cleavage of the cis double bonds of unsaturated fatty acids by NaIO4/OsO4 produced the omega-oxo fatty acids; subsequent reduction by [3H]NaBH4 afforded a series of highly radioactive [omega-3H]hydroxy fatty acids to which a variety of photoreactive probes can be readily attached. In this study, the m-diazirinophenoxy group was coupled to the omega-hydroxy groups of the fatty acids, yielding the omega-(m-diazirinophenoxy) derivatives of nonanoic, undecanoic, tridecanoic, and pentadecanoic acid. These photoreactive derivatives were incorporated by L-cells into their major phospholipids; in addition, a number of proteins were shown to be acylated by these fatty acids. The photoreactive group was shown to remain intact as indicated by the cross-linking of the resulting photoreactive phospholipids to other phospholipids as well as to a number of L-cell proteins upon photolysis. This procedure thus identifies integral membrane proteins and directly produces photoaffinity derivatives of those proteins normally acylated by fatty acids.

Animals↗