Activity of fatty acyl CoA-lysophospholipid acyltransferases in liver microsomes of rats fed a choline-deficient diet

Lipids ◽  
1973 ◽  
Vol 8 (4) ◽  
pp. 163-165 ◽  
Author(s):  
S. -H. Chen ◽  
B. Lombardi
Keyword(s):  
Liver Microsomes ◽  
Fatty Acyl ◽  
Deficient Diet ◽  
Lysophospholipid Acyltransferases

scholarly journals Fatty acyl-CoA esters inhibit glucose-6-phosphatase in rat liver microsomes

1995 ◽  
Vol 307 (2) ◽  
pp. 391-397 ◽  
Author(s):  
R Fulceri ◽  
A Gamberucci ◽  
H M Scott ◽  
R Giunti ◽  
A Burchell ◽  
...  
Keyword(s):  
Palmitic Acid ◽  
Phosphatase Activity ◽  
Rat Liver ◽  
Liver Microsomes ◽  
Fatty Acyl ◽  
Rat Liver Microsomes ◽  
Control Value ◽  
Scattering Measurements ◽  
Induced Changes ◽  
Enzymic Assay

In native rat liver microsomes glucose 6-phosphatase activity is dependent not only on the activity of the glucose-6-phosphatase enzyme (which is lumenal) but also on the transport of glucose-6-phosphate, phosphate and glucose through the respective translocases T1, T2 and T3. By using enzymic assay techniques, palmitoyl-CoA or CoA was found to inhibit glucose-6-phosphatase activity in intact microsomes. The effect of CoA required ATP and fatty acids to form fatty acyl esters. Increasing concentrations (2-50 microM) of CoA (plus ATP and 20 microM added palmitic acid) or of palmitoyl-CoA progressively decreased glucose-6-phosphatase activity to 50% of the control value. The inhibition lowered the Vmax without significantly changing the Km. A non-hydrolysable analogue of palmitoyl-CoA also inhibited, demonstrating that binding of palmitoyl-CoA rather than hydrolysis produces the inhibition. Light-scattering measurements of osmotically induced changes in the size of rat liver microsomal vesicles pre-equilibrated in a low-osmolality buffer demonstrated that palmitoyl-CoA alone or CoA plus ATP and palmitic acid altered the microsomal permeability to glucose 6-phosphate, but not to glucose or phosphate, indicating that T1 is the site of palmitoyl-CoA binding and inhibition of glucose-6-phosphatase activity in native microsomes. The type of inhibition found suggests that liver microsomes may comprise vesicles heterogeneous with respect to glucose-6-phosphate translocase(s), i.e. sensitive or insensitive to fatty acid ester inhibition.

A Study on the Effect of Lysolecithin and Phospholipase A on Membrane-Bound Galactosyltransferase

1974 ◽  
Vol 52 (11) ◽  
pp. 1053-1066 ◽  
Author(s):  
Sailen Mookerjea ◽  
James W. M. Yung
Keyword(s):  
Liver Microsomes ◽  
Fatty Acyl ◽  
Phospholipase A ◽  
Synthetase Activity ◽  
Rat Liver Microsomes ◽  
Physiological Concentration ◽  
Activation Effect ◽  
Membrane Bound ◽  
Hydrolysis Of

Addition of lysolecithin caused very marked activation of UDP-galactose:glycoprotein galactosyltransferase in rat liver microsomes and in Golgi-rich membranes. Lysolecithin activated galactosyltransferase when the enzyme was assayed both with endogenous acceptor and with exogenous proteins or monosaccharides as acceptors. Lactose synthetase activity in presence of α-lactalbumin was also stimulated by lysolecithin. Lecithin, lysophosphatidylethanolamine, lysophosphatidic acid, and glycerophosphorylcholine did not activate the enzyme, suggesting that both fatty acyl and phosphorylcholine groups of the lysolecithin molecule are required for the observed activation. The degree of activation was about the same when myristoyl-, palmitoyl-, oleoyl-, or stearoyllysolecithin were tested. The activation by lysolecithin was observed well within the physiological concentration of the lipid in the liver cell. Saturating amounts of Triton masked the effect of lysolecithin.Brief preincubation with phospholipase A activated the enzyme and generated lysolecithin in the membranes. Triton and lysolecithin activated the enzyme without any lag time, whereas phospholipase A activation was dependent on preincubation and also on an alkaline pH favorable for the hydrolysis of phospholipid. EDTA blocked the activation effect of phospholipase A but had no effect on activation by lysolecithin. Albumin and cholesterol opposed the effects of lysolecithin and phospholipase A on the enzyme. Two successive incubations of the microsomes with lysolecithin caused considerable release of the enzyme into the soluble fraction. The role of lysolecithin in the activation of the enzyme is probably related to the solubilization of the membrane and consequent enhanced interaction of the enzyme with substrate. Lysolecithin also activated N-acetylglucosaminyl- and sialyltransferase activities in microsomes. A possible role of lysolecithin is indicated in the regulation of glycosylation reactions in mammalian system.

scholarly journals Effect of selenium deficiency on hepatic lipid and lipoprotein metabolism in the rat

1997 ◽  
Vol 78 (3) ◽  
pp. 493-500 ◽  
Author(s):  
F. Nassir ◽  
C. Moundras ◽  
D. Bayle ◽  
C. Sérougne ◽  
E. Gueux ◽  
...  
Keyword(s):  
Plasma Cholesterol ◽  
Liver Microsomes ◽  
Ldl Receptor ◽  
Selenium Deficiency ◽  
Cholesterol Concentration ◽  
Deficient Diet ◽  
Hmg Coa Reductase ◽  
Hepatic Lipid ◽  
Se Deficiency ◽  
Coa Reductase

Since experimental Se deficiency results in a significant increase in plasma cholesterol concentration the present investigation was undertaken to assess further the influence of this deficiency on the expression of proteins involved in hepatic lipid metabolism. Se deficiency was induced by feeding weanling male Wistar rats on a deficient diet for 6 weeks. Hypercholesterolaemia associated with Se deficiency was related to increased 3-hydroxy-3-methylglutaryl-coA (HMG-CoA) reductase (EC 1.1.1.34) activity in liver microsomes as compared with control animals. Hepatic lipoprotein receptor levels (LDL-receptor and HDL-binding proteins, HB1 and HB2) were not significantly affected by Se deficiency, as assessed by immunoblotting. Plasma triacylglycerol concentrations tended to decrease in Se-deficient rats in concert with their reduced post-Triton secretion. There was no significant effect of Se deficiency on the hepatic synthesis of apolipoproteins. These results point to the need for further investigations into the mechanism related to the increased activity of HMG-CoA reductase and the enhanced cholesterogenesis in the liver of Se-deficient rats likely to result from this.Selenium: Cholesterol: Triacylglycerol: HMG-CoA reductase

Changes in lipid composition of liver microsomes and fatty acyl-CoA desaturase activities induced by medium chain triglyceride feeding

Lipids ◽  
1989 ◽  
Vol 24 (5) ◽  
pp. 383-388 ◽  
Author(s):  
José L. Periago ◽  
María L. Pita ◽  
María A. Sanchez del Castillo ◽  
Guillermo Caamaño ◽  
María D. Suárez
Keyword(s):  
Lipid Composition ◽  
Liver Microsomes ◽  
Medium Chain Triglyceride ◽  
Fatty Acyl ◽  
Medium Chain

scholarly journals Activation of a peroxisome-proliferating catabolite of cholic acid to its CoA ester

1993 ◽  
Vol 296 (1) ◽  
pp. 265-270 ◽  
Author(s):  
T Nishimaki-Mogami ◽  
A Takahashi ◽  
Y Hayashi
Keyword(s):  
Cholic Acid ◽  
Rat Liver ◽  
Microsomal Fraction ◽  
Liver Microsomes ◽  
Subcellular Fractionation ◽  
Fatty Acyl ◽  
Peroxisome Proliferator ◽  
Rat Liver Microsomes ◽  
Triton X ◽  
Long Chain

We have shown that a microbial cholic acid catabolite (4R)-4-(2,3,4,6,6a beta,7,8,9,9a alpha,9b beta-decahydro-6a beta-methyl-3-oxo- 1H-cyclopenta[f]quinolin-7 beta-yl)valeric acid (DCQVA), is a potent peroxisome proliferator. In this paper a possible key stage in DCQVA metabolism, the activation of DCQVA to its CoA ester, has been investigated in rat liver microsomes and particulate fractions. The microsomal reaction was dependent on CoA, ATP, DCQVA (0.2-1 mM) and protein content. The reaction was decreased by storage at 4 degrees C, preincubation of microsomes at 37 degrees C for 5 min, or inclusion of Triton X-100 in the reaction mixture. Such treatments also enhanced generation of long-chain fatty acyl-CoAs, as determined by h.p.l.c. analysis. The same effect was caused by exposing the microsomes to phospholipase A2, suggesting that endogenous fatty acids may compete with DCQVA for esterification with CoA. Subcellular fractionation of rat liver demonstrated that the activity of DCQVA-CoA synthesis was localized predominantly in the microsomal fraction, in contrast to long-chain fatty acyl-CoA synthetase, which was distributed among all particulate fractions. Administration of clofibrate of rats did not affect the distribution of DCQVA-CoA synthesis activity. In contrast to a 2-fold induction of long-chain fatty acyl-CoA synthetase by clofibrate treatment, the activity of DCQVA-CoA synthesis in the microsomal fraction decreased by 80%. These results suggest that DCQVA is activated by an enzyme distinct from long-chain fatty acyl-CoA synthetase. The resulting perturbation of fatty acid metabolism may be involved in the mechanism whereby DCQVA causes peroxisome proliferation.

scholarly journals Up-regulation of liver glucose-6-phosphatase in rats fed with a Pi-deficient diet

1999 ◽  
Vol 343 (2) ◽  
pp. 393-396 ◽  
Author(s):  
Wensheng XIE ◽  
Yazhou LI ◽  
Marie-Claire MÉCHIN ◽  
Gérald VAN DEWERVE
Keyword(s):  
Glycogen Content ◽  
Control Diet ◽  
Liver Microsomes ◽  
Catalytic Subunit ◽  
Protein Abundance ◽  
Deficient Diet ◽  
Pi Transport ◽  
Nutritional Conditions ◽  
G6pase Activity ◽  
Pi Deficiency

Because Pi deprivation markedly affects the Na/Pi co-transporter in kidney and has been related to insulin resistance and glucose intolerance, the effect of a Pi-deficient diet on the liver microsomal glucose-6-phosphatase (G6Pase) system was investigated. Rats were fed with a control diet (+Pi) or a diet deficient in phosphate (-Pi) for 2 days and killed on the morning of the third day, after an overnight fast (fasted) or not (fed). Kinetic parameters of Pi transport (t½ and equilibration) into liver microsomes were not changed by the different nutritional conditions. In contrast, it was found that G6Pase activity was significantly increased in the (-Pi) groups. This was due to an increase in the Vmax of the enzyme, without change in the Km for G6P. There was no correlation between liver microsomal glycogen content and G6Pase activity, but both protein abundance and mRNA of liver 36 kDa catalytic subunit of G6Pase (p36) were increased. The mRNA of the putative G6P translocase protein (p46) was changed in parallel with that of the catalytic subunit, but the p46 immunoreactive protein was unchanged. These findings indicate that dietary Pi deficiency causes increased G6Pase activity by up-regulation of the expression of the 36 kDa-catalytic-subunit gene.

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