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At least 253 records · Page 14Linked to original sources
PubMed1989

Cholesterol metabolism by purified cytochrome P-450scc is highly stimulated by octyl glucoside and stearic acid exclusively in large unilamellar phospholipid vesicles.

Cholesterol side-chain cleavage (CSCC) catalyzed by purified bovine adrenal mitochondrial cytochrome P-450scc is highly dependent on the vesicles that supply cholesterol. Six-fold higher rates are achieved with large unilamellar dioleoylphosphatidylcholine vesicles (diameter 150 nm) prepared by octyl glucoside (OG) dialysis (DOPC-LUV) than with small sonicated vesicles (diameter 30 nm) (DOPC-SUV) (Vmax = 25 and 4 min-1, respectively. Extensive dialysis that may remove OG decreased Vmax rates for DOPC-LUV almost to rates seen with DOPC-SUV. These dialyzed DOPC-LUV were, however, very sensitive to addition of OG (EC50 = 2.5 microM, 4.3-fold stimulation) while DOPC-SUV were only weakly affected (EC50 = 100 microM, 1.6-fold stimulation). This enhancement of CSCC in LUV by OG only occurred when the cholesterol:DOPC exceeded 0.1 and was associated with a 15-fold increase in the Km for cholesterol. Structural changes in both SUV and LUV at high cholesterol:DOPC ratios (0.1-1) were indicated by decreases in internal volume that were insensitive to OG and did not affect the external diameters. Stearic acid produced a similar stimulation of CSCC in LUV (EC50 = 50 microM) and had no effect on SUV. The Vmax for CSCC, produced by OG activation of DOPC-LUV, is comparable to the highest attained for cytochrome P-450scc (Tween 20/cholesterol). In LUV, a minor proportion of OG (1-5% of cholesterol) is thus sufficient to generate a domain of reactive cholesterol that maintains a near-optimum turnover. This increased CSCC was paralleled by increased binding of cholesterol to P-450scc, suggesting that this cholesterol is more readily donated by the membrane to the cytochrome.

Animals↗
PubMed1979

beta-Oxidation of the coenzyme A esters of elaidic, oleic, and stearic acids and their full-cycle intermediates by rat heart mitochondria.

beta-Oxidation rates for the CoA esters of elaidic, oleic and stearic acids and their full-cycle beta-oxidation intermediates and for the carnitine esters of oleic and elaidic acids were compared over a wide range of substrate and albumin concentrations in rat heart mitochondria. The esters of elaidic acid were oxidized at about half the rate of the oleic acid esters, while stearoyl-CoA was oxidized equally as rapid as oleoyl-CoA. The full-cycle beta-oxidation intermediates of elaidoyl-CoA (trans-16 : 1 delta 7, -14 : 1 delta 5, and -12 : 1 delta 3) were found to be oxidized at rates nearly equal to those for the corresponding intermediates of oleoyl-CoA. Therefore, after the first cycle of beta-oxidation, oleoyl-CoA and elaidoyl-CoA are oxidized at nearly equal rates. The activity of fatty acyl-CoA dehydrogenase was higher with elaidoyl-CoA and its full-cycle intermediates as substrates than with the corresponding cisisomers. It was concluded that the slower oxidation rate of elaidic acid is not due to slower oxidation of any of its full-cycle beta-oxidation intermediates, nor to slower activity of fatty acyl-CoA dehydrogenase, nor to outer mitochondrial carnitine acyltransferase. Possible explanations to account for the slower oxidation rate of elaidic acid are discussed.

Acyl Coenzyme A↗
PubMed1999

Effect of synthetic triglycerides of myristic, palmitic, and stearic acid on serum lipoprotein metabolism.

OBJECTIVES: To determine relative effects of diets high in synthetic sources of myristic (14:0), palmitic (16:0) or stearic (18:0) acid on concentrations and metabolism of serum lipoproteins. DESIGN: Eighteen healthy women participated in a three-way cross-over study for five week periods separated by seven week washout periods, diets were assigned in random order. SUBJECTS: Premenopausal women, not on medication, were from three races (Caucasian, African-American, Asian) and four apolipoprotein E phenotype groups (3/3, 3/2, 4/3, and 4/2). INTERVENTION: During the first week the subjects consumed a baseline diet providing 11 energy (en)% saturated fat, 10en% polyunsaturated fat and 14en% monounsaturated fat. Followed by test diets with 19en% saturated fat (including 14en% test saturated fatty acid), 3en% polyunsaturated fat, and 14en% monounsaturated fat for four weeks. Synthetic fats (trimyristin, tripalmitin, and tristearin) were used in blends with natural fats and oils. RESULTS: Mean concentrations of serum total, esterified and LDL cholesterol were significantly lower after 18:0 than after 16:0 (n = 16-18, P < 0.01 for treatment effect). Myristic acid (14:0) had an intermediate effect. Receptor-mediated degradation of 125I-LDL in mononuclear cells obtained from the subjects was lower after 16:0 than after 14:0 and 18:0 (n = 16-18, P=0.05 for treatment effect). Differences in the digestibilities of the fats were not a major factor in the results. Strong cholesterolemic responses to the 16:0 diet were partly explained by apoE phenotype. CONCLUSIONS: As noted previously, stearic acid was neutral compared to 14:0 and 16:0. In contrast to studies involving natural fats, 14:0, fed as a synthetic triglyceride, was less cholesterolemic than 16:0 in a majority of subjects. ApoE phenotype influenced the cholesterolemic response particularly when diets high in 16:0 were eaten.

Adult↗
PubMed1998

The reaction of lanthanide ions with n-doxyl stearic acids and its utilization for the ESR study on the permeability of lipid-bilayer of erythrocyte membrane to gadolinium ions.

The reaction of lanthanide ions with n-doxyl stearic acid (nDS) spin labels (n = 5,7,12,16) was investigated by the electron spin resonance technique in aqueous solution. Among the lanthanides, the Gd3+, Tb3+, Tm3+ and Ce3+ ions strongly quenched the ESR signal of spin labels, but the effects of La3+, Eu3+ and Lu3+ are very weak. The quenching effects are featured by: (1) the dependence on the concentration of lanthanide ions; (2) no obvious changes of the ESR line shape in the presence of lanthanide ions; (3) the quenching constant decreases in the order: Gd3+ > Tb3+ > Tm3+ > Ce3+; (4) the quenching effects of lanthanide ions are found to strikingly correlate with their magnetic properties. These findings indicate that the interaction of lanthanide ions with nitroxide oxygen leading to the reduction of ESR signal amplitude is dominated by their magnetic characteristics rather than the coordination effect. By labeling erythrocyte membrane with nDS, n = 5,7,12,16 at different depths, we studied the diffusion of Gd3+ into the lipid-bilayer of erythrocyte membrane by monitoring the reduction processes of the ESR signals of nitroxide spin labels located at different depths of membrane lipid-bilayer after addition of Gd3+. These results revealed that the Gd3+ ions can penetrate into the lipid-bilayer, though the entry rate is slow. It was shown that the Gd3+ ions bind to the membrane and enhance the permeability of extracellular ascorbate into erythrocyte membrane. The transport mechanism of Gd3+ ions through the lipid-bilayer might be involved in the Gd3+ cation-induced pore formation in the surface of membrane.

Ascorbic Acid↗
PubMed1979

The role of insulin in the regulation of stearic acid desaturase activity in liver and adipose tissue from obese--hyperglycaemic (ob/ob) and lean mice.

The relationship between the hyperinsulinaemia of obese--hyperglycaemic (ob/ob) mice and their high activity of stearic acid delta 9-desaturase compared with lean mice has been investigated. The concentrations of plasma insulin in obese mice were decreased by 71, 88 and 96% after treatment either with alloxan or food restriction to maintain the same weight as lean mice, or treatment of the weight restricted mice with alloxan followed by feeding ad libitum. The concentration of plasma insulin produced by the latter treatment was the same as in normal lean mice. After treatment the hepatic desaturase activities were 24, 68 and 19% less respectively on a cell basis than in livers from untreated obese mice, and the total epididymal fat-pad activities were lower by 16, 62 and 57%. These results suggest that hyperinsulinaemia is not essential for the increased hepatic desaturase, controlling the hepatic desaturase activity, but even this may be subject to overriding regulation by the concentration of esterified linoleic acid in the liver lipids, which was negatively correlated (r = 0.91, P less than 0.001) with desaturase activity.

Adipose Tissue↗
PubMed1975

[Studies on the stearic acid dehydrogenase in the liver and brain of rats of various ages (author's transl)].

Tissue slices from the liver and brain of 7-day-old rats incubated with [1-14C]stearic acid desaturate the stearate to oleate. The activities of the two tissues are different but of the same order of magnitude. With increasing age, the activity in the liver increases markedly, while the brain activity decreases. The postmitochondrial supernatant from adult (3-month-old) liver contains 2 to 3 orders of magnitude more stearoyl-CoA dehydrogenase activity than the brain postmitochondrial fraction. The washed microsomal fraction from liver had about the same activity as the postmitochondrial supernatant, but no dehydrogenase activity could be detected in the washed microsomal fraction from the brain. The acyl-CoA synthetase and the palmitoyl-CoA hydrolase activities measured in the washed microsomes from adult brain were both lower than in liver microsomes. The concentration of stearoyl-CoA (the substrate for the stearoyl-CoA dehydrogenase) resulting from the ratio of these activities was too high, however, for the lack of desaturase activity to have been simulated by lack of substrate.

Aging↗
PubMed1993

Synthesis of alpha,alpha-trehalose 2,3- and 2,3'-diesters with palmitic and stearic acid: potential immunoreactants for the serodiagnosis of tuberculosis.

Regioselective monoacylation, by the stannylation method, of 4,6:4',6'-di-O-benzylidene-alpha,alpha-trehalose with palmitoyl or stearoyl chloride afforded the 2-palmitate and 2-stearate of the diacetal, whereas partial diacylation led to the corresponding 2,3'-dipalmitate and 2,3'-distearate. Protection of the monoesters in the 2',3' positions by cyclizing silylation with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane, followed by acylation of the silyl ethers, gave the fully protected 2,3-dipalmitate, 2,3-distearate, and 2-palmitate-3-stearate. Small proportions of other isomers and triesters were also produced in these reactions. Desilylation and debenzylidenation of the diesters finally furnished 2,3- and 2,3'-di-O-palmitoyl-2,3- and 2,3'-di-O-stearoyl-, and 2-O-palmitoyl-3-O-stearoyl-alpha,alpha-trehalose.

Antigen-Antibody Reactions↗
PubMed1991

Hypoxia-stimulated reduction of doxyl stearic acids in human red blood cells. Role of hemoglobin.

Nitroxide free radicals are under active investigation for their potential use as metabolically responsive contrast agents in electron paramagnetic resonance and nuclear magnetic resonance imaging. The metabolism in human red blood cells of lipid-soluble nitroxides, doxyl stearic acids (DSA), has been investigated. We observed that under normoxia DSA were stable in red blood cells for at least 2 h, but hypoxia stimulated spin label reduction. Complete signal recovery after air or ferricyanide oxidation suggested the formation of hydroxylamine during hypoxia. DSA reduction was found to be dependent upon the position of the nitroxide ring in the fatty acid chain with the reduction rate higher when the -NO degree of the doxyl ring was closer to the fatty acid carboxylic end. The reduction kinetics of DSA with the doxyl ring nearest to the carboxylic end (5DSA) was bifasic. A rapid reduction of about half of the 5DSA was observed in the first hour and, thereafter, a slow reduction process become predominant. The slope of the slow reduction abruptly decreased below 5 microM, thus suggesting a concentration-dependent membrane-cytoplasm translocation of 5DSA. The reducing activity of the red blood cell (RBC) was completely recovered in the cell lysate. Under hypoxia, purified hemoglobin and myoglobin reduced 5DSA and a complete recovery of the signal was obtained after air reoxidation. Globin did not reduce 5DSA, while methemoglobin showed only a small reduction of 5DSA, thus suggesting that ferrous-heme was involved in the hypoxic reduction of DSA. both DSA localization and the characteristics of intracellular reductant (hemoglobin) are responsible for the high stability of DSA in the RBC.

Cyclic N-Oxides↗