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PubMed1982

Alkyldihydroxyacetone-P synthase. Solubilization, partial purification, new assay method, and evidence for a ping-pong mechanism.

Alkyldihydroxyacetone-P (alkyl-DHAP) synthase, the enzyme that forms the ether linkage of alkyl and alk-1-enyl glycerolipids, has been solubilized from ehrlich ascites cell microsomes using Triton X-100 and acetone precipitation. the solubilized enzyme, which is stabilized by glycerol or ethylene glycol, was then purified further by chromatography on DEAE-cellulose, QAE-Sephadex, Matrex Red, and hydroxylapatite with the aid of a new rapid assay method using DEAE-cellulose disks. Four enzymes involved in the metabolism of acyl-DHAP and alkyl-DHAP (acyl-DHAP/alkyl-DHAP oxidoreductase, DHAP acyltransferase, alkyl-DHAP phosphohydrolase, and a dinitrofluorobenzene-insensitive acyl-DHAP acylhydrolase) are removed under these conditions along with endogenous fatty acids and fatty alcohols. Two other activities copurify with the alkyl-DHAP synthase forward reaction: an acyl exchange reaction, in which [1-14C]palmitic acid is incorporated into palmitoyl-DHAP, and an alkyl exchange reaction, in which [1-14C]hexadecanol is incorporated into hexadecyl-DHAP. Exchange reactions of this type are characteristic properties of a ping-pong mechanism but not a sequential mechanism. This is confirmed by documentation that palmitic acid is a competitive inhibitor with respect to hexadecanol. In addition, low levels of palmitoyl-DHAP (less than 100 microM) show competitive inhibition with respect to hexadecanol, possibly due to palmitic acid formed from palmitoyl-DHAP by alkyl-DHAP synthase under these conditions. Based on the observations presented here and previously, a molecular mechanism for alkyl-DHAP synthase is proposed.

Alkyl and Aryl Transferases↗
PubMed1988

The Rh polypeptide is a major fatty acid-acylated erythrocyte membrane protein.

The erythrocyte Rh antigens contain an Mr = 32,000 integral protein which is thought to contribute in some way to the organization of surrounding phospholipid. To search for possible fatty acid acylation of the Rh polypeptide, intact human erythrocytes were incubated with [3H]palmitic acid prior to preparation of membranes and sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. Several membrane proteins were labeled, but none corresponded to the glycophorins or membrane proteins 1-8. An Mr = 32,000 band was prominently labeled on Rh (D)-negative and -positive erythrocytes and could be precipitated from the latter with anti-D. No similar protein was labeled on membranes from Rhmod erythrocytes, a rare phenotype lacking Rh antigens. Labeling of the Rh polypeptide most likely represents palmitic acid acylation through thioester linkages. The 3H label was not extracted with chloroform/methanol, but was quantitatively eluted with hydroxylamine and co-chromatographed with palmitohydroxamate and free palmitate by thin layer chromatography. The fatty acid acylations occurred independent of protein synthesis and were completely reversed by chase with unlabeled palmitate. It is concluded that the Rh polypeptide is fatty acid-acylated, being a major substrate of an acylation-deacylation mechanism associated with the erythrocyte membrane.

Acylation↗
PubMed1984

Lignoceric acid is oxidized in the peroxisome: implications for the Zellweger cerebro-hepato-renal syndrome and adrenoleukodystrophy.

The deficient oxidation and accumulation of very-long-chain fatty acids in the Zellweger cerebro-hepato-renal syndrome (CHRS) and X chromosome-linked adrenoleukodystrophy (ALD), coupled with the observation that peroxisomes are lacking in CHRS, prompted us to investigate the subcellular localization of the catabolism of lignoceric acid (C24:0). Peroxisomal and mitochondrial-rich fractions were separated from rat liver crude mitochondria by sucrose density gradient centrifugation. Enzyme activity for the oxidation of [1-14C]palmitic acid to water-soluble acetate was 2- to 3-fold higher in the mitochondrial than in the peroxisomal-rich fraction whereas [1-14C]lignoceric acid was oxidized at a 2- to 3-fold higher rate in the peroxisomal than in the mitochondrial fraction. Moreover, unlike palmitic acid oxidation, lignoceric acid oxidation was not inhibited by potassium cyanide in either rat liver fractions or human skin cultured fibroblasts, showing that lignoceric acid is mainly and possibly exclusively oxidized in peroxisomes. We also conducted studies to clarify the striking phenotypic differences between CHRS and the childhood form of ALD. In contrast to CHRS, we found normal hepatocellular peroxisomes in the liver biopsy of a childhood ALD patient. In addition, in the presence of potassium cyanide, the oxidation of palmitic acid in cultured skin fibroblasts was inhibited by 62% in control and X chromosome-linked ALD patients compared with 88% in CHRS and neonatal ALD. This differential effect may be related to differences in peroxisomal morphology in those disorders.

Abnormalities, Multiple↗
PubMed1995

A novel neuropeptide cellular mechanism in amphibian interrenal steroidogenesis.

Interrenals of female Rana esculenta were incubated with gonadotropin-releasing hormone (GnRH), 9-ketoreductase inhibitor (palmitic acid), acetyl salicyclic acid, prostaglandin F2 alpha (PGF2 alpha), forskolin, isobutylmethyl xanthine (IBMX), dibutyril cyclic adenosine monophosphate (dbcAMP). Prostaglandin E2 (PGE2), PGF2 alpha, testosterone and 17 beta-estradiol were assessed on the incubation media. In addition, in the same interrenals, 9-ketoreductase and aromatase activities were evaluated. GnRH increased PGF2 alpha, 17 beta-estradiol, 9-ketoreductase and aromatase, and decreased PGE2 and testosterone. PGF2 alpha increased 17 beta-estradiol and aromatase, and decreased testosterone. Palmitic acid counteracted GnRH effects, while forskolin, IBMX and dbcAMP showed the same PGF2 alpha effects. These results suggest that GnRH stimulates 9-ketoreductase enhancing PGF2 alpha which in turn activates aromatase through cAMP mediation in the interrenal of Rana esculenta.

1-Methyl-3-isobutylxanthine↗
PubMed2004

Epitope mapping of a monoclonal antibody specific to bovine dry milk: involvement of residues 66-76 of strand D in thermal denatured beta-lactoglobulin.

beta-Lactoglobulin (beta-LG) is a bovine milk protein sensitive to thermal denaturation. Previously, we demonstrated that such structural change can be detected by a monoclonal antibody (mAb) specific to denatured beta-LG. In the present study, we show a dramatic increase in beta-LG immunoreactivity when heating raw milk between 70 and 80 degrees C. To map out the specific epitope of beta-LG recognized by this mAb, we used a combined strategy including tryptic and CNBr fragments, chemical modifications (acetylation and carboxymethylation), peptide array containing in situ synthesized peptides, and a synthetic soluble peptide for immunoassays. The antigenic determinant we defined was exactly located within the D strand (residues 66-76) of beta-LG. Circular dichroic spectral analysis shows that carboxymethylation on beta-LG not only resulted in a substantial loss of beta-configuration but also exerted a 10 times increase in immunoreactivity as compared with heated beta-LG. The result suggests that a further disordered structure occurred in beta-LG and thus rendered the mAb recognition. Mutations on each charged residue (three Lys and one Glu) revealed that Lys-69 and Glu-74 were extremely essential in maintaining the antigenic structure. We also show an inverse relationship between the immunoreactivity in heated beta-LG and its binding to retinol or palmitic acid. Most interestingly, pH 9-10, which neutralizes the Lys groups of beta-LG, not only reduced its immunoreactivity but also its binding to palmitic acid implicating a role of Lys-69. Taken together, we concluded that strand D of beta-LG participated in the thermal denaturation between 70 and 80 degrees C and the binding to retinol and palmitic acid. The antigenic and biochemical roles of mAb specific to D strand are discussed in detail.

Amino Acid Sequence↗
PubMed1987

Inhibition of 12-O-tetradecanoylphorbol-13-acetate induction of ornithine decarboxylase activity, DNA synthesis, and tumor promotion in mouse skin by ascorbic acid and ascorbyl palmitate.

The effects of topically applied 12-O-tetradecanoylphorbol-13-acetate (TPA) on the level of ascorbic acid in the epidermis and the effects of topically applied ascorbic acid, ascorbyl palmitate (a synthetic lipophilic derivative of ascorbic acid), palmitic acid and sorbitan monopalmitate on TPA-induced epidermal ornithine decarboxylase activity, epidermal DNA synthesis, and the promotion of skin tumors were evaluated in female CD-1 mice. Topical application of 5 or 16 nmol of TPA resulted in a 45-50% decrease in the amount of ascorbic acid per mg protein in mouse epidermis at 5 h after TPA application. Large topical doses of ascorbic acid inhibited TPA-induced tumor promotion in mouse epidermis, but smaller doses were inactive. The topical application of relatively small doses of ascorbyl palmitate had a marked inhibitory effect on TPA-induced ornithine decarboxylase activity, DNA synthesis, and tumor promotion in mouse epidermis. Ascorbic acid, palmitic acid, and sorbitan monopalmitate were less effective than ascorbyl palmitate as inhibitors of tumor promotion. The topical application of 4 mumol of ascorbyl palmitate inhibited by 60-76% the induction of epidermal ornithine decarboxylase activity and DNA synthesis that occurred after a single topical application of 2 nmol of TPA whereas similar doses of ascorbic acid had no inhibitory effect. The topical application of 4 mumol of ascorbyl palmitate together with 5 nmol of TPA twice weekly for 20 weeks to previously initiated mice inhibited by 91% the number of tumors per mouse.

Administration, Topical↗
PubMed1985

The synthesis and secretion of gastric mucus glycoprotein by mucosal cells cultured in the presence of ethanol.

The effect of ethanol on the synthesis and secretion of mucus glycoprotein in gastric mucosal cells was investigated. The mucosal cell suspensions were subjected to a short-term (4 h) culture in the presence of 0-1.5 M ethanol, with [3H]proline and [3H]palmitic acid as markers for glycoprotein synthesis and acylation. The synthesized labeled mucus glycoprotein was isolated from the incubation medium (extracellular glycoprotein) and from the mucosal cells (intracellular glycoprotein), and analyzed. Depending upon the ethanol concentration in the cell culture medium, two distinct effects on the synthesis and secretion of mucus glycoprotein were observed. The cells cultured in the presence of 0.02-0.1 M ethanol showed increased ability for the incorporation of [3H]proline and [3H]palmitic acid, and for the secretion of the newly assembled mucus glycoprotein. The synthesis of the glycoprotein increased 18-fold, acylation 5-fold, and secretion 10-fold. The synthesized glycoprotein, however, contained four to five times less of acyl-bound fatty acids. Ethanol at 0.1-1.5 M caused a marked reduction (62-64%) in the mucus glycoprotein synthesis, but the amount of glycoprotein released to the medium remained constant. This indicated that higher concentrations of ethanol caused the release of the preformed intracellular mucus glycoprotein reserves. The results demonstrate that gastric mucosal cells incubated in the presence of ethanol exhibit impaired synthesis and secretion of mucus glycoprotein, and that the severity of impairment depends upon the ethanol concentration.

Animals↗
PubMed1983

Effects of retinol, retinal, retinoic acid, retinyl palmitate and retinyl acetate on HeLa cell viability.

A study has been made of the effects of retinoic acid, retinal, retinol, retinyl palmitate and retinyl acetate on HeLa cell viability. The results obtained show that (i) these cells seem to be more resistant to vitamin A than other cell cultures; (ii) the various vitamin A compounds differ in their inhibitory action on HeLa cells; (iii) the effects of retinoic acid, retinal, retinol and retinyl acetate are cytotoxic, those of retinyl palmitate are always cytolytic.

Cell Survival↗
PubMed1979

Quantitative chromatographic method for the determination of low levels of nitrilotriacetic and ethylenediaminetetraacetic acids in diethylenetriaminepentaacetic acid.

A quantitative method for determination of low levels (0.05%, w/w) of nitrilotriacetic and ethylenediaminetetraacetic acids in diethylenetriaminepentaacetic acid is described. Palmitic acid is added to the chelator as an internal standard before esterification with methanol containing 2%(v/v)H2SO4. The methyl esters of palmitic, nitrilotriacetic, and ethylenediaminetetraacetic acids are first separated from diethylenetriaminepentaacetate by silicic acid column chromatography and are subsequently quantitated by gas-liquid chromatography. The method is both accurate and reproducible with less than 10% relative error. Thin-layer chromatographic separations of the methyl esters, and quantitation at the 1% level, are also described.

Acetates↗
PubMed1990

Fatty acid composition of erythrocyte membrane lipid obtained from children suffering from kwashiorkor and marasmus.

The fatty acid composition of erythrocyte membrane (EM) lipids obtained from normal, kwashiorkor, and marasmic children was analyzed by gas chromatography. The proportion of palmitic acid (16:0) was lower and of oleic acid (18:1) higher in the kwashiorkor group than in the control group. The marasmic group showed lower proportions of eicosatrienoic acid (20:3) and arachidonic acid (20:4) and a higher proportion of oleic acid (18:1) than the control group. A significant difference was found between the marasmic and kwashiorkor groups with respect to arachidonic acid (20:4), which showed a lower proportion in the former group than the latter. The ratio of arachidonic acid to linoleic acid (20:4/18:2) was markedly lower in the marasmic group than the control group, suggesting a possible impairment in the conversion of linoleic acid to arachidonic acid in marasmic children. The ratio of unsaturated fatty acids to saturated fatty acids was markedly elevated in the kwashiorkor group over that of control group, indicating increased fluidity of EM in kwashiorkor. It is suggested that the altered membrane fatty acid composition reflects deranged lipid metabolism and affects the physical and physiological properties of EM and could contribute to changes in the activities of several red blood cell membrane-bound enzymes reported earlier in kwashiorkor children.

Child, Preschool↗
PubMed1999

[The compositional analysis of phospholipids and their fatty acids in rabbit sarcoplasmic reticulum].

Phospholipids were extracted from the sarcoplasmic reticulum of rabbit skeletal muscle, and separated by high performance thin layer chromatography. The mole fraction of individual phospholipids were determined by assaying phosphorus of each band. Main phospholipids were scraped and extracted, and subjected to esterification by alkaline methanol, and then the composition and content of fatty acids were determined by gas chromatography. The results show that the main phospholipid components were PC (phosphatidylcholine) and PE (phosphatidylethanolamine). They account for 66.5% and 15.5%, respectively. The main fatty acid in PC is palmitic acid and those in PE are stearic acid and arachidic acid.

Animals↗
PubMed1993

Hexadecylpalmitoylglycerol or ceramide is linked to similar glycophosphoinositol anchor-like structures in Trypanosoma cruzi.

The lipopeptidophosphoglycan from Trypanosoma cruzi is a glycosylated inositol-phosphoceramide isolated from epimastigotes at the stationary phase of growth (4-5 days). We have now purified two similar glycoinositolphospholipids (glycoinositolphospholipid A and glycoinositolphospholipid B) from epimastigotes after the second day of culture growth. [3H]Palmitic acid was incorporated into 1-O-hexadecyl-2-O-palmitoylglycerol in glycoinositolphospholipid A and into ceramide in glycoinositolphospholipid B. The lipids were released by incubation with glycosylphosphatidylinositol-specific phospholipase C from Bacillus thuringiensis or by chemical methods. After alkaline hydrolysis, the lipids were analysed by GLC/MS. In glycoinositolphospholipid A the resulting lipids corresponded to 1-O-hexadecylglycerol and palmitic acid. The ceramide components in glycoinositolphospholipid B are sphinganine, palmitic acid and lignoceric acid. The oligosaccharides could be degraded by nitrous acid and further enzymic treatment showed that the two glycoinositolphospholipids isolated from T. cruzi share the common core structure of the glycosylphosphatidylinositol membrane anchors. The microheterogeneity was determined, as well as the substitution by galactose, and was mainly in the furanose configuration as was previously described for lipopeptidophosphoglycan. However, methylation analysis indicated that 20% of the galactose is in the pyranose form. Both glycoinositolphospholipids mainly differ in the lipid moiety.

Animals↗
PubMed2001

5-Hydroxytryptamine 4(a) receptor expressed in Sf9 cells is palmitoylated in an agonist-dependent manner.

The mouse 5-hydroxytryptamine 4(a) receptor [5-HT(4(a))] was expressed with a baculovirus system in insect cells and analysed for acylation. [(3)H]Palmitic acid was effectively incorporated into 5-HT(4(a)) and label was sensitive to the treatment with reducing agents indicating a thioester-type bond. Analysis of protein-bound fatty acids revealed that 5-HT(4(a)) contains predominantly palmitic acid. Treatment of infected Sf9 (Spodoptera frugiperda) cells with BIMU8 [(endo-N-8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2,3-dehydro-2-oxo-3-(prop-2-yl)-1H-benzimid-azole-1-carboxamide], a 5-HT(4) receptor-selective agonist, generated a dose-dependent increase in [(3)H]palmitate incorporation into 5-HT(4(a)) with an EC(50) of approx. 10 nM. The change in receptor labelling after stimulation with agonist was receptor-specific and did not result from general metabolic effects. We also used both pulse labelling and pulse-chase labelling to address the dynamics of 5-HT(4(a)) palmitoylation. Incorporation studies revealed that the rate of palmitate incorporation was increased approx. 3-fold after stimulation with agonist. Results of pulse-chase experiments show that activation with BIMU8 promoted the release of radiolabel from 5-HT(4(a)), thereby reducing the levels of receptor-bound palmitate to approximately one-half. Taken together, our results demonstrate that palmitoylation of 5-HT(4(a)) is a reversible process and that stimulation of 5-HT(4(a)) with agonist increases the turnover rate for receptor-bound palmitate. This provides evidence for a regulated cycling of receptor-bound palmitate and suggests a functional role for palmitoylation/depalmitoylation in 5-hydroxytryptamine-mediated signalling.

Amino Acid Sequence↗
PubMed1993

A tightly membrane-associated subpopulation of spectrin is 3H-palmitoylated.

A tightly membrane-associated form of spectrin (TMA-spectrin) was labeled when human red blood cells were incubated with [3H]palmitic acid. About 90% of spectrin was not fatty acid-acylated and was extracted from membranes by low salt buffers. The 3H-palmitoylated TMA-spectrin, however, resisted low and even high salt extraction and remained associated with inside-out vesicles that were generated in the process of spectrin-actin extraction from membranes. TMA-spectrin was preferentially extracted from KCl-stripped vesicles by 5 M urea at low ionic strength. TMA-spectrin was purified by gel filtration and by ion exchange chromatography in the presence of urea and a non-ionic detergent. Purified TMA-spectrin was 3H-palmitoylated exclusively in the beta subunit to 0.28 mol/mol after a 12-h incubation of red cells. The labeled palmitate may be bound as an ester or thioester, since hydroxylamine (1 M, pH 7.5) released the label completely. Peptide maps of 3H-palmitoylated TMA-spectrin showed three or two labeled peptides from the beta subunit, when generated by V8 protease and trypsin, respectively. Two types of antibodies to spectrin reacted with purified TMA-spectrin, and TMA-spectrin contained the same antigenic peptides as low salt-extractable spectrin. Rabbit anti-ankyrin antibodies did not bind to TMA-spectrin. The substoichiometric incorporation of [3H]palmitic acid into TMA-spectrin could result from the slow turnover of endogenously bound fatty acids. Generation of the tightly membrane-associated and 3H-palmitoylated subpopulation of spectrin cannot be due to entrapment of an unmodified residual fraction of spectrin in right-side-out vesicles. Instead, the data suggest the existence of a subpopulation of spectrin molecules that undergo a covalent fatty acid modification and thereby alter their binding properties. This may offer a new, metabolically dependent mechanism for dynamic interactions between spectrin and the membrane lipid bilayer.

Electrophoresis, Polyacrylamide Gel↗
PubMed1989

Intramyelinic conversion of cerebrosides into acylgalactosylceramides.

Acylgalactosylceramide (AGC) synthesis was measured in vivo, and in a cell free system. 24 hours post-injection of [3H] palmitic acid into rat brain, more than 60% of the AGC radioactivity was associated with an ester linkage. Isolated rat myelin was incubated in the presence of [14C] palmitic acid, 2mM ATP, 50 microM CoA and 10 mM MgCl2 and acylation of myelin cerebrosides occurred at a linear rate for at least 60 min. Incubation of isolated myelin under standard conditions with [3H] cerebrosides and [14C] palmitic acid produced double labeled AGC. Labeling of AGC was maximum at pH 7.5 and 37 degrees C and appeared to be enzyme mediated inasmuch as it was reduced by myelin incubation with trypsin and drastically reduced by preheating the myelin for 5 min at 80 degrees C. Omission of ATP, CoA, MgCl2 or all three did not reduce fatty acid incorporation into AGC when compared to the values in the complete system. Addition of Triton X100 or Sodium Dodecyl Sulfate had little or no effect on the acylation of cerebrosides. Pulse chase experiments indicated that the reaction involved the net addition of fatty acid to the cerebrosides, rather than a rapid fatty acid exchange.

Animals↗
PubMed1988

Myristylation of rotavirus proteins.

After labelling with [3H]myristic acid during replication the structural proteins VP6 and VP2 of purified rotavirus particles were found to be myristylated in an amide bond. [3H]Palmitic acid was converted to myristic acid before bonding to the viral proteins. Possible functions of rotavirus protein myristylation are discussed.

Capsid↗
PubMed1990

A stimulatory effect of FFA on glycolysis unmasked in cells with impaired oxidative capacity.

The physiological importance of the glucose fatty acid cycle has been controversial. Many studies have failed to demonstrate an inhibitory effect of free fatty acids (FFA) on glucose utilization. Using both hepatoma cells (Hep G2) and human erythrocytes, which have poor oxidative capacity and metabolize glucose primarily anaerobically, we have demonstrated a unique stimulatory effect of FFA on glycolysis. Fructose 2,6-bisphosphate (F-2,6-P2) concentrations also increased significantly in Hep G2 cells incubated with palmitic acid. In contrast, F-2,6-P2 concentrations fell in primary cultured hepatocytes incubated with palmitic acid in association with increased oxidation of FFA and accumulation of beta-hydroxybutyrate. We propose that a stimulatory effect of FFA on glycolysis reported here for the first time may have been masked in previous studies performed in tissues in which the oxidation of FFA and the accumulation of intermediates such as citrate may have decreased F-2,6-P2 concentrations. We conclude that the spectrum of FFA effects in glycolysis probably depends on tissue oxidative capacity.

Animals↗