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At least 523 records · Page 29Linked to original sources
PubMed1988

Oxidation of 1-O-(alk-1-enyl)-2,3-di-O-acylglycerols: models for plasmalogen oxidation.

Alk-1-enyl diacyl glycerides, model compounds for plasmalogen lipids, were synthesized for use as substrates in oxidation studies. The neutral plasmalogen glycerides prepared included 1-O-(hexadec-1-enyl)-2,3-di-O-stearoylglycerol (4a) and 1-O-(hexadec-1-enyl)-2-O-linoleoyl-3-O-stearoylglycerol (4b). Oxidative disappearance of these glycerides was followed directly by high performance liquid chromatography (HPLC). The extent of oxidation of the side chains of these glycerides, i.e. the alkenyl ether and fatty acyl functions, was monitored by conversion of the side chains to dimethylacetal and methyl ester by methanolysis, followed by subsequent gas chromatography (GC) of the methanolysis products. Both analytical approaches show that the alkenyl ether function of neat 4a oxidizes more slowly than neat ethyl linoleate. However, the rate of alkenyl ether loss from 4a is accelerated in the presence of added ethyl linoleate. Moreover, when the linoleoyl group is incorporated into the 2-position of the alkenyl glyceride, as in 4b, the rate of loss of the alkenyl group was shown to be similar to the rate of loss of the linoleoyl group. These results suggest that oxidation of plasmalogen glycerides should not be ignored as a factor that contributes to the oxidative instability of animal tissue.

Chromatography, Gas↗
PubMed1981

Inhibition of phosphoenolpyruvate carboxykinase, glyceroneogenesis and fatty acid synthesis in rat adipose tissue by quinolinate and 3-mercaptopicolinate.

To study the interrelationships of phosphoenolpyruvate carboxykinase and glyceroneogenesis in adipose tissue, investigations with two effectors of the hepatic carboxykinase, Fe2+ and Mn2+, and two inhibitors of the enzyme and of gluconeogenesis in liver, quinolinic acid and 3-mercaptopicolinic acid, were carried out. Incubating adipose tissue cytosol with 30 microM Fe2+ or 100 microM Mn2+ prior to assaying for phosphoenolpyruvate carboxykinase activity doubled the enzyme activity. Inhibition of the enzyme by quinolinate alone was minimal. Adding 30 microM Fe2+ to the cytosol decreased the K0.5 (concentration that gives 50% inhibition) for quinolinate to 0.4 mM and the K0.5 for mercaptopicolinate from 200 to 14 microM. Activating the enzyme with 100 microM Mn2+ did not lower the K0.5 values and adding 500 microM Mn2+ to the cytosol completely interfered with the enhancement of inhibition induced by Fe2+. Each inhibitor interfered with 14C incorporation into glyceride glycerol from labeled pyruvate, alanine and lactate in suspensions of adipocytes. Adding 1 mM Mn2+ to the adipocyte suspension almost completely prevented the inhibition of pyruvate and alanine incorporation into glyceride glycerol, but adding the Mn2+ or 250 microM Fe2+ to the adipocytes in the absence of inhibitors did not enhance glyceride glycerol formation. Adding 250 microM Fe2+ to the adipocytes did not enhance inhibition of lipid synthesis by mercaptopicolinate or quinolinate. Mercaptopicolinate did not inhibit glyceride glycerol, fatty acid, total lipid or CO2 production from glucose. The lack of activation of glyceride glycerol synthesis by added Fe2+ or Mn2+, the lack of enhancement of pyridine carboxylate inhibition by Fe2+ and the interference with inhibition by Mn2+ are compatible with the idea that a transition metal ion similar to Fe2+, if not Fe2+ itself, is available to, or loosely bound to, the adipose tissue carboxykinase in vivo. Taken together with the results of previous work which showed ferroactivator (a cytosol protein necessary for Fe2+ activation of the carboxykinase) to be present in adipose tissue, the present results indicate that the control of the adipose tissue carboxykinase may be similar to the enzyme in liver. Fatty acid synthesis was also diminished by the inhibitors, albeit to a lesser extent than was glyceride glycerol formation. It is hypothesized that this was secondary to decreased esterification caused by the lack of glycerol 3-phosphate from inhibition of the carboxykinase. Decreased esterification would lead to a build-up of fatty acyl CoA which inhibits fatty acid synthesis.

Adipose Tissue↗
PubMed1969

Effects of prolonged incubation and cell concentration on lipogenesis from glucose in isolated human omental fat cells.

The behavior of human omental fat cells in vitro has been examined in order to define conditions under which glucose is converted to glyceride-glycerol and glyceride fatty acids. Synthesis of glyceride fatty acids from glucose reached maximal rates only after several hours of incubation in Krebs-Henseleit bicarbonate buffer, with or without added bovine albumin. Conversion of glucose to glyceride fatty acids was readily demonstrable with concentrated cell suspensions and was stimulated 3- to 8-fold by insulin. With dilute cell suspensions, little fatty acid was synthesized even after prolonged incubation in the presence of insulin. Conversion of glucose to glyceride-glycerol was linear during 6-hr incubations in buffer and unaffected by the concentration of the cell suspension. In the presence of bovine albumin, glyceride-glycerol synthesis was readily demonstrable at all cell concentrations used, although synthesis was faster in dilute suspensions. Thus, different incubation conditions produce widely divergent patterns of glucose metabolism in human omental fat cells.

Adipose Tissue↗
PubMed1967

Effect of propionate on pyruvate metabolism in adipose tissue.

Glyceride-glycerol formation in rat adipose tissue from pyruvate-2-(14)C is increased by fasting, while fatty acid synthesis is markedly depressed. In tissues of fasted animals glyceride-glycerol formation is maximal with concentrations of pyruvate exceeding 2.5 mM. With 0.25 mM pyruvate-2-(14)C, glyceride-glycerol formation is increased severalfold by the addition of 0.25 mM propionate. No further increase in synthesis is caused by propionate when pyruvate is supplied in optimal amounts. Addition of equimolar concentrations of acetate or pyruvate does not replace propionate. The effect of propionate on glyceride-glycerol synthesis from pyruvate is also given by a series of even-chain fatty acids. However, only propionate promotes fatty acid synthesis in tissues of fasted and fed animals. Fixation of (14)CO(2) in glyceride-glycerol is dependent on the presence of propionate and is maximal in tissues of fasted rats and when pyruvate is also added. Succinate has no significant effect. Actinomycin treatment blocks glyceride-glycerol synthesis in tissues of fed and fasted animals, in the presence and absence of propionate. At the same time, fatty acid synthesis in tissues of fasted rats is markedly increased.

Adipose Tissue↗