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PubMed1986

Fractionation of membrane proteins by temperature-induced phase separation in Triton X-114. Application to subcellular fractions of the adrenal medulla.

After solubilization with the detergent Triton X-114, membrane proteins may be separated into three groups: if the membrane is sufficiently lipid-rich, one family of hydrophobic constituents separates spontaneously at low temperature; warming at 30 degrees C leads to separation of a detergent-rich phase and an aqueous phase. Using the chromaffin-granule membrane as a model, we found that many intrinsic membrane glycoproteins are found in the latter phase, probably maintained in solution by adherent detergent. They precipitate, however, when this is removed by dialysis, leaving in solution those truly hydrophilic proteins that were originally adhering to the membranes. We have used this method with mitochondria, and with Golgi- and rough-endoplasmic-reticulum-enriched microsomal fractions: it has proved to be a rapid and convenient method for effecting a partial separation of proteins from a variety of different membranes.

Adenosine Triphosphatases↗

PubMed1967

The biosynthesis of cytochrome c. Sequence of incorporation in vivo of [14C]lysine into cytochrome c and total proteins of rat-liver subcellular fractions.

1. In order to determine the initial intracellular site of synthesis of cytochrome c in the liver cell, groups of rats were injected with [(14)C]lysine and killed 7.5, 15, 30 and 60min. later. The livers were homogenized in 0.3m-sucrose and subcellular fractions obtained. The mitochondrial fraction was further subfractionated. Pure cytochrome c was isolated from extracts of each fraction, obtained first with water at pH4.0 and then with 0.15m-sodium chloride. 2. A comparison of the kinetics of incorporation of [(14)C]lysine into total protein for each particulate fraction showed the usual two different kinds of kinetics. Incorporation into all the mitochondrial subfractions and the nuclear fraction rose gradually to a plateau value at about 20min., in contrast with that into the two microsomal fractions which rose rapidly to a peak value about seven times that for the mitochondrial fractions. The kinetics for the incorporation into mitochondrial cytochrome c showed a plateau value at 30min. about three times that for the total mitochondrial protein. There was no difference in the specific radioactivity of the mitochondrial cytochrome c extracted with water or 0.15m-sodium chloride or between the different mitochondrial subfractions. In contrast, the cytochrome c isolated from water extracts of the microsomal fractions had a lower specific radioactivity than that obtained from the 0.15m-sodium chloride extract. The specific radioactivity of the latter showed a rapid rise to a peak value about four times that for the mitochondrial cytochrome c, and the shape of the curve was similar to that for the total protein of the microsomal fraction. The results suggest that cytochrome c is synthesized in toto by the morphological components of the microsomal fraction. It seems first to be bound tightly to a microsomal particle, passing then to a looser microsomal binding and being finally transferred to the mitochondria. The newly synthesized cytochrome c in the mitochondrion could not be differentiated from the old by its degree of extractability at pH 4.0.

Animals↗

PubMed1989

A novel lectin-gold density perturbation eliminates plasma membrane contaminants from Golgi-enriched subcellular fractions.

The availability of pure Golgi fractions is a prerequisite for documenting the composition of the membranes of the Golgi Complex and comparing and contrasting this organelle with the rough endoplasmic reticulum. In a companion article, we have described a subcellular fractionation protocol for rat myeloma cells which effectively eliminates rough microsomes from Golgi-enriched fractions. Nevertheless, a major overlap with plasma membrane remains. We have therefore developed a novel density perturbation procedure to eliminate plasma membrane contaminants. By binding a conjugate of wheat germ agglutinin and colloidal gold to cells at 4 degrees C before homogenization we cause extensive sedimentation of plasma membrane markers to the "mitochondrial pellet" as well as a major shift in the isopycnic density of these markers. The differential and isopycnic sedimentation of several Golgi markers is unaffected in lectin-gold treated cells. The Golgi-enriched fractions obtained by isopycnic sedimentation are therefore of high purity. This procedure may be of general use for either purifying or eliminating plasma membrane-derived vesicles. Adaptations of the method might be equally useful for density perturbation of intracellular organelles.

Animals↗

PubMed1975

Glycerolipid metabolism in cellular and subcellular fractions of fasted rat liver.

The effect of overnight fasting on glycerolipids of the rat liver organelles was studied. The concentration of microsomal phospholipids was markedly decreased by fasting, whereas that of mitochondria and whole liver increased significantly. The significant increase due to fasting in the activity of microsomal phosphorylcholine-glyceride transferase appeared to be responsible for the increased concentration of hepatic phospholipid. The incorporation by the liver slice of [1(-14)C] glycerol into PC3 in mitochondria was increased by fasting, while there was no difference in the microsomal fraction containing supernatant. The significant decrease in the relative proportions of oleic and linoleic acids and a significant increase in stearic and arachidonic acids in phosphatidylcholine were observed in the intact liver as well as its subcellular fractions. The possible relationship of these changes after fasting to the similarity in the incorporation pattern of [1(-14)C] glycerol into the molecular species of these glycerolipids was demonstrated.

Animals↗

PubMed1987

Subcellular fractionation of the longitudinal smooth muscle/myenteric plexus of dog ileum: dissociation of the distribution of two plasma membrane marker enzymes.

The distribution of plasma membrane markers, the sodium pump [evaluated as ouabain-sensitive, potassium-stimulated p-nitrophenyl phosphatase (K+-pNPPase)], [3H]saxitoxin binding, and 5'-AMPase, was studied in the subcellular fractions prepared from the homogenates of the longitudinal smooth muscle/myenteric plexus of dog ileum. The K+-pNPPase activity and [3H]-saxitoxin binding were found to be predominantly associated with the synaptosomal fraction as indicated by the high level of these activities in the crude synaptosomal fraction and by the copurification of K+-pNPPase and [3H]saxitoxin binding, but not 5'-AMPase, with several synaptosomal markers during the fractionation of the crude synaptosomal fraction on density gradients. In contrast to the K+-pNPPase activity and [3H]saxitoxin binding, the 5'-AMPase activity was found to be concentrated in the microsomal pellet. Further fractionation of microsomes on density gradient resulted in copurification of 5'-AMPase but not K+-pNPPase or [3H]saxitoxin binding, with other smooth muscle plasma membrane-bound enzymes, such as high-affinity Ca2+-ATPase, Mg2+-ATPase, and Ca2+-ATPase. It was concluded that in the longitudinal smooth muscle/myenteric plexus, the sodium pump activity is present in higher density in the neuronal plasma membranes whereas 5'-AMPase activity is concentrated in the smooth muscle plasma membranes.

4-Nitrophenylphosphatase↗

PubMed1979

Glycosphingolipids of subcellular fractions from normal rat liver and Morris hepatoma 5123TC.

Neutral glycosphingolipids and gangliosides were quantified in lipid extracts from plasma membranes, mitochondria, microsomes, and nuclei isolated from normal rat liver and Morris hepatoma 5123TC. Results showed a higher content of glycosphingolipids, especially gangliosides, in hepatomas and differences in the distribution of glycosphingolipids among subcellular fractions. Differences in the glycosphingolipid composition of the hepatoma, namely, the absence of trisialogangliosides and an increase in the lower molecular weight gangliosides, reflected an altered metabolism of glycosphingolipids in this tumor. The results indicated that changes in membrane glycosphingolipids were not restricted to the cell surfaces of malignant cells, inasmuch as intracellular membrane fractions also exhibited altered glycosphingolipid profiles.

Animals↗

PubMed1973

Localization of Na + , K + -ATPase and other enzymes in teleost pseudobranch. I. Biochemical characterization of subcellular fractions.

In an effort to determine the subcellular localization of sodium- and potassium-activated adenosine triphosphatase (Na(+), K(+)-ATPase) in the pseudobranch of the pinfish Lagodon rhomboides, this tissue was fractionated by differential centrifugation and the activities of several marker enzymes in the fractions were measured. Cytochrome c oxidase was found primarily in the mitochondrial-light mitochondrial (M+L) fraction. Phosphoglucomutase appeared almost exclusively in the soluble (S) fraction. Monoamine oxidase was concentrated in the nuclear (N) fraction, with a significant amount also in the microsomal (P) fraction but little in M+L or S. Na(+), K(+)-ATPase and ouabain insensitive Mg(2+)-ATPase were distributed in N, M+L, and P, the former having its highest specific activity in P and the latter in M+L. Rate sedimentation analysis of the M+L fraction indicated that cytochrome c oxidase and Mg(2+)-ATPase were associated with a rapidly sedimenting particle population (presumably mitochondria), while Na(+), K(+)-ATPase was found primarily in a slowly sedimenting component. At least 75% of the Na(+), K(+)-ATPase in M+L appeared to be associated with structures containing no Mg(2+)-ATPase. Kinetic properties of the two ATPases were studied in the P fraction and were typical of these enzymes in other tissues. Na(+), K(+)-ATPase activity was highly dependent on the ratio of Na(+) and K(+) concentrations but independent of absolute concentrations over at least a fourfold range.

Adenosine Triphosphatases↗

PubMed1987

Ethoxyresorufin O-deethylase activity in rat brain subcellular fractions.

Non-polar, lipid-soluble drugs or xenobiotics are able to cross the blood-brain barrier. The brain cytochrome P-450-dependent monooxygenases may oxidize these molecules to more polar and somewhat hazardous metabolites responsible for neurotoxicity. In order to characterize the cytochrome P-450 dependent aryl hydrocarbon hydroxylase activity in brain subcellular fractions, we used 7-ethoxyresorufin as a substrate, as its O-deethylation reflects specifically the activity of the cytochrome P-450 isoform which metabolizes and is induced by polycyclic aromatic hydrocarbons. The results reported here show that this enzymatic activity occurs in both microsomal and mitochondrial fractions, and that the induction after 3-methylcholanthrene treatment remains limited, thus preventing the formation of high levels of harmful metabolites.

Animals↗

PubMed1992

Furosemide decreases eggshell thickness and inhibits 45Ca2+ uptake by a subcellular fraction of eggshell gland mucosa of the domestic fowl.

1. Administration of furosemide to egg-laying domestic fowl (single p.o. dose 100 mg/bird) caused a decrease in the thickness of the shell of eggs laid the next day. 2. Furosemide administration in vivo caused a 37% decrease in the uptake of 45Ca2+ by a subcellular fraction of the eggshell gland mucosa (mainly composed of cell fragments and plasma membranes). 3. Furosemide treatment did not affect calcium concentrations in plasma or shell gland fluid but did cause a significant increase in the calcium concentration in shell gland mucosa. 4. It is concluded that the eggshell-thinning effect of furosemide is localized to an inhibitory effect on plasma membrane calcium transport in the eggshell gland mucosa. 5. These findings are discussed and compared with the effects of other drugs and toxic substances known to influence eggshell formation in birds.

Animals↗

PubMed1998

Localization of motilin binding sites in subcellular fractions from rabbit antral and colonic smooth muscle tissue.

BACKGROUND AND AIM: Motilin stimulates gastrointestinal motility, but in vitro studies reveal a direct smooth muscle effect, whereas in vivo studies reveal a neurally mediated effect. The aim of the present study was to determine if motilin binds to microsomes (smooth muscle) and/or synaptosomes (neurons). METHODS: Subcellular fractions were prepared from tissue of rabbit gastric antrum and colon by differential centrifugation and density gradient centrifugation and characterized by determining motilin binding and the presence of membrane markers. RESULTS: The purified microsomal fraction, enriched in the smooth muscle marker 5'-nucleotidase, was found to have the highest specific motilin binding in both antrum and colon. In the antrum, but not in the colon, the mitochondrial fraction also showed enrichment of [3H]-saxitoxin binding (marker for synaptosomes) and motilin binding, although the latter was much lower than in the microsomal fraction. Two receptor binding sites were characterized in both the antral mitochondrial/synaptosomal and colonic microsomal fraction (antrum: pKd,1 9.89+/-0.19, pKd,2 8.18+/-0.11, colon: pKd,1 9.72+/-0.31, pKd,2 8.39+/-0.58). CONCLUSION: Motilin binding is predominantly associated with smooth muscle membranes in both antrum and colon of the rabbit. In both organs two motilin binding sites are present with comparable affinities, but the density in the colon is much higher for both sites. Whether they represent neural and smooth muscle receptors will require studies with isolated smooth muscle cells and neurons.

Animals↗

PubMed1998

Alpha-tocopherol in rat brain subcellular fractions is oxidized rapidly during incubations with low concentrations of peroxynitrite.

The reaction of superoxide (a reactive oxygen species) and nitric oxide (one of the nitrogen oxides with numerous biological functions) results in the production of peroxynitrite. The characteristics of oxidation of alpha-tocopherol (vitamin E) in synaptosomes (nerve ending particles) and mitochondria by peroxynitrite were studied. The subcellular fractions were isolated from brain hemispheres of 4-month-old male Fischer 344 rats by standard centrifugation procedures involving Ficoll gradients. Peroxynitrite treatment oxidized alpha-tocopherol in <5 s. This reaction was selective because another membrane component, cholesterol, was not oxidized at the same time, as observed in our previous studies. Mitochondrial alpha-tocopherol was more susceptible to peroxynitrite-induced oxidation than synaptosomal tocopherol. Measurable and significant (P < 0.05) oxidation of tocopherol occurred when mitochondria or synaptosomes were incubated with peroxynitrite in concentrations as low as 5 or 10 micromol/L, respectively. The oxidation could be readily monitored by estimating the production of tocopherolquinone. Oxidation of tocopherol induced by ferrous iron and ascorbate was much slower and the yield of tocopherolquinone lower than by peroxynitrite. The fast and selective oxidation of alpha-tocopherol by peroxynitrite suggests that vitamin E may play an important role in preventing membrane oxidation induced by peroxynitrite. Literature reports indicate the existence of threshold concentrations of tocopherol below which functional alterations occur. Tocopherol oxidation by peroxynitrite could reduce tocopherol concentrations in tissues and subcellular structures to these threshold levels by different concentrations of peroxynitrite. Hence the sensitivity of tissues to peroxynitrite could vary over a wide range.

Animals↗

PubMed1995

Subcellular fractions of cyclic AMP and cyclic AMP-dependent protein kinase and the positive inotropic effects of selective beta 1- and beta 2-adrenoceptor agonists in guinea pig hearts.

We studied the effects of a full beta 1-adrenoceptor agonist (T-0509), a beta 2-adrenoceptor agonist (procaterol) and a nonselective beta-adrenoceptor agonist (isoproterenol, ISO) on subcellular cyclic AMP levels and cyclic AMP-dependent protein kinase (cyclic AMP-PK) activity in guinea pig hearts and compared them with the effect of each drug on cardiac contractility. T-0509 (10(-8)M) and ISO (3 x 10(-8)M) caused an increase of approximately 170% in dF/dtmax, whereas 10(-7) procaterol produced only a 25% increase. All these agonists significantly increased the cyclic AMP level in ventricular homogenate. Subcellular fractions were obtained by centrifugation at 100,000 g for 10 min and by Li2SO4 precipitation of the 100,000-g supernatant. In the control heart, probably salcolemmal protein, phospholamban, and 60-kDa protein in the particulate fraction and probably troponin I and troponin C in the supernatant fraction were mainly phosphorylated by the catalytic subunit of cyclic AMP-PK. In the precipitate obtained from the supernatant fraction with Li2SO4, probably all proteins described were contained. However, none of the proteins were detected in the supernatant obtained with Li2SO4. T-0509 and ISO caused significant changes in cyclic AMP levels and cyclic-PK activities in all fractions. However, procaterol increased the cyclic AMP concentrations and cyclic AMP-PK activities only in the supernatant fraction and the supernatant obtained with Li2SO4. T-0509 and ISO increased cyclic AMP level (9-16 pmol/mg protein) and cyclic AMP-PK activity ratio (0.27-0.33) significantly to the same degree in the precipitate obtained with Li2SO4, whereas the effects of T-0509 in other fractions were about twofold less than those of ISO. These results suggest that beta 1- and beta 2-adrenoceptor agonists cause differential compartmentalization of cyclic AMP and cyclic AMP-PK in the cardiac muscle.

Adrenergic alpha-Agonists↗

PubMed1982

The effect of chronic ethanol administration on lipids and fatty acids in subcellular fractions of rat brain.

In this study we have investigated the proportion of lipids and of fatty acids in brain membranes and blood serum from rats which received ethanol over a long period. Nine Sprague-Dawley rats were given ethanol in their drinking water for five months. Nine age-matched rats given pure water served as controls. Subcellular fractions (myelin, synaptosomes and mitochondria) were prepared in a discontinuous gradient of sucrose from each of the 18 rats. Blood serum was collected at decapitation. The fractions were assayed for their concentrations of protein, cholesterol, phospholipids and for the proportions of fatty acids in individual phosphoglycerides. No significant differences in the concentration of the major lipids were obtained between the ethanol-exposed rats and the control rats. In the synaptosomal fraction from ethanol-exposed rats, the proportion of oleic acid in phosphatidylcholine was increased and that of arachidonic acid in phosphatidylethanolamine decreased. These two fatty acids were also changed in the blood serum and there was a significant correlation between the changes in the brain and blood serum. The results suggest that during ethanol exposure there is an increased disposition toward modification of synaptosomal membranes by changes in the blood plasma fatty acid pattern.

Animals↗

PubMed1993

Metabolism and bioactivation of 3-methylindole by Clara cells, alveolar macrophages, and subcellular fractions from rabbit lungs.

3-Methylindole (3MI), a fermentation product of tryptophan produced by intestinal and ruminal microflora, has been shown to cause pneumotoxicity in several species subsequent to cytochrome P450-mediated biotransformation. Among several species studied, rabbits are comparatively resistant to 3MI-induced pneumotoxicity, especially when compared to goats or mice. In this study, rabbit pulmonary cells and subcellular fractions were used to examine the metabolism and bioactivation of 3MI. A covalent-binding metabolite was produced in 3MI incubations by both Clara cells and macrophages. The addition of the cytochrome P450 inhibitor, 1-aminobenzotriazole, to these incubations inhibited the production of covalent-binding metabolite(s) by 94% in Clara cells and only 24% in macrophages. In incubations of Clara cells or macrophages with 3MI and N-acetylcysteine (NAC), a polar conjugate was detected and tentatively identified as an adduct of 3-hydroxy-3-methylindolenine (3H3MIN). Also identified were 3[(N-glutathione-S-yl)-methyl]-indole (3MI-GSH) and 3-methyloxindole (3MOI). In rabbit lung microsomal incubations with 3MI and glutathione (GSH), 3MI-GSH, 3MOI, indole-3-carbinol, and a GSH adduct of 3H3MIN were identified. The addition of cytosol to the microsomal incubations with GSH did not increase the rate of formation of the GSH adducts, indicating that cytosolic GSH-S-transferases are not essential in the formation of these metabolites. GSH significantly decreased the covalent binding of an electrophilic metabolite in microsomal incubations. These data suggest that GSH may be important in the mitigation of 3MI toxicity. Furthermore, the comparison of 3MI bioactivation to electrophilic intermediates in Clara cells and alveolar macrophages suggests that 3MI is metabolized by different oxidative pathways in the two different cell types, although the same metabolites were produced by the two cell types. This study shows that rabbit pulmonary enzymes are capable of bioactivating 3MI to reactive intermediates which become covalently bound to cellular macromolecules. This indicates that the relative resistance of rabbits to 3MI-induced pneumotoxicity is probably not due to differences in metabolic enzymes which convert 3MI to reactive intermediates.

Acetylcysteine↗

PubMed2005

In vitro conjugation of ethanolamine with fatty acids by rat liver subcellular fractions.

Previous studies from our laboratory have shown the enzymic formation of fatty acid (FA) conjugates of xenobiotic alcohols and amines. In the present study, the formation of FA conjugates of a bifunctional compound, ethanolamine was investigated by incubating [1-14C]oleic acid (1 mM) with ethanolamine (25 mM) at 37 degrees C in the presence of various rat liver subcellular fractions. The resultant product (or products) was separated by thin-layer chromatography (TLC) and the radioactivity corresponding to the relative flow of fatty acid amide was determined. Under similar conditions, formation of ethanolamides of palmitic, stearic, linoleic, linolenic, and arachidonic acids were also examined. The formation of ethanolamine conjugate with oleic acid was found to be 16.3 nmol/h/mg protein as compared to 6.7, 6.2, 8.1, 8.3, and 7.6 nmol/h/mg protein for palmitic, stearic, linoleic, linolenic, and arachidonic acids, respectively. The formation of oleoyl ethanolamide was found to be 18.9, 40.1, 65.9, and 0.3 nmol/h/mg protein in postnuclear, mitochondrial, microsomal, and cytosolic fractions, respectively. Mass spectrometric and nuclear magnetic resonance spectroscopic data of the TLC-purified product confirm the formation of oleoyl ethanolamide, and amidation appeared to be a preferred reaction over esterification. The results of this study suggest that the enzyme responsible for the amidation of fatty acids resides mainly in the microsomal fraction of the liver, and that oleic acid is a better substrate than other fatty acids used in the present study.

Analysis of Variance↗

PubMed1975

Amino acid incorporation into brain subcellular fractions in experimental allergic encephalomyelitis.

The in vitro protein synthetic capactiy of brain slices from guinea-pigs in the late stage (17-18 days post-induction) of experimental allergic encephalomyelitis was increased over that of Freund's adjuvant injected controls, as determined by the rate of (14C)-leucine incorporation into both tris-soluble and tris-insoluble proteins. All subcellular fractions prepared from incubated slices showed increased incorporation, with a crude nuclear fraction having the largest increase. Isolated brain mitochondria from EAE animals incorporated more amino acid into protein during the late stage of the disease, while isolated microsomes and "pH5 enzymes" show decreased amino acid incorporation compared with controls in the late stage of EAE. Polyacrylamide gel electrophoresis of acidic, soluble proteins isolated from (3H)-leucine labeled nuclear or synaptosomal fractions revealed that increases of incorporation were generalized, and not restricted to a few proteins.

Amino Acids↗

PubMed1975

[Decanoic acid, new precursor for in vitro biosynthesis of oleic acid by a plant subcellular fraction].

Various membraneous fractions prepared from a cauliflower homogenate synthesize radioactive oleic acid when they are incubated in a 14C-decanolate solution. The more active fraction is formed of vesicles sedimenting at 30,000 g x 20 mn (heavy microsomes). The labelled precursor is transformed by this fraction mainly into oleic acid and hydroxyacids. ATP, NADPH, CoA and oxygen are required for these reactions. Labelled fatty acids, longer than lauric and (i.e. 14C-myristic, 14C-palmitic and 14C-stearic acids) are not transformed into oleic acid by the subcellular fraction studied in this paper.

Adenosine Triphosphate↗

PubMed1975

[Studies on the appearance of chalone proteins in the subcellular fractions from some bovine tissues. I. Antimitotic activity, the level of proteins, nucleic acids and glycoproteins in healthy cattle and in that affected with leukosis].

The occurrence of chalones has been studied in the liver, spleen and lymph nodes of cattle. The cells of those organs were fractionated. After removing the nuclei and mitochondria the residue was subdivided by means of the cesium chloride gradient into smooth and rough microsomes. The chalones were investigated in supernatants from these two groups of microsomes. In the obtained supernatants, the levels of proteins, nucleic acids and glycoproteins were estimated. The protein composition was analysed by means of disc electrophoresis on polyacrylamide, and the antigenic relationship of these proteins with the serum ones was studied using immunoelectrophoresis. The biological value of the separated fractions was investigated by means of the mitosis inhibition test in mice. The experimental groups of these animals were injected intraperitoneally with different cellular subfractions without or with colcemide. The control groups were treated with colcemide only or with physiological solution of NaCl. The subcellular fractions were separated from the tissues of healthy cattle and of that affected with leukosis. It was found that a protein showing chalone activity appears in all cellular subfractions derived from the tissues of healthy animals; its highest concentration was found in the supernatants from rough microsomes of the spleen and from smooth microsomes of the lymph nodes. The antimitotic effect was observed at the concentration of 100-200 microg of protein in 0.1 ml. This effect seems to be connected with glycoproteins. In the supernatants from tissues of leukotic animals, there was observed a decrease of the antimitotic effect. A mixture of proteins was present in the supernatants, which was demonstrated by means of polyacrylamide electrophoresis. These proteins showed and antigenic relationship with the proteins of blood serum. This can be concluded from their precipitation with the sera against the bovine serum proteins in the immunoelectrophoresis test. The chalone of the spleen seems to be different from that of the lymph nodes. The experiment showed the occurrence of an antimitotic effect with the non-homologous proteins, i.e. the chalone from the liver inhibited the mitotic divisions of the cells of the spleen, thymus and lymph nodes in mice. In this experiment, a mixture of proteins was used. The purification of an active chalone will be the subject of further investigations.

Animals↗