The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform

Dennis E. Vance - One of the best experts on this subject based on the ideXlab platform.

  • localization of the pe methylation pathway and sr bi to the canalicular membrane evidence for apical pc biosynthesis that may promote biliary excretion of phospholipid and cholesterol
    Journal of Lipid Research, 2003
    Co-Authors: Ephraim Sehayek, Dennis E. Vance, Rong Wang, Vadim S Zinchuk, Elizabeth M Duncan, S Shefer, Meenakshisundaram Ananthanarayanan, Brian T Chait, Jan L Breslow
    Abstract:

    : To better understand the regulation of biliary phospholipid and cholesterol excretion, canalicular membranes were isolated from the livers of C57BL/6J mice and abundant proteins separated by SDS-PAGE and identified by matrix-assisted laser desorption/ionization mass spectrometry. A prominent protein revealed by this analysis was betaine homocysteine methyltransferase (BHMT). This enzyme catalyzes the first step in a three-enzyme pathway that promotes the methylation of Phosphatidylethanolamine (PE) to phosphatidylcholine (PC). Immunoblotting confirmed the presence of BHMT on the canalicular membrane, failed to reveal the presence of the second enzyme in this pathway, methionine adenosyltransferase, and localized the third enzyme of the pathway, PE N-methyltransferase (PEMT). Furthermore, immunfluorescence microscopy unambiguously confirmed the localization of PEMT to the canalicular membrane. These findings indicate that a local mechanism exists in or around hepatocyte canalicular membranes to promote phosphatidylethnolamine methylation and PC biosynthesis. Finally, immunoblotting revealed the presence and immunofluorescence microscopy unambiguously localized the scavenger receptor class B type I (SR-BI) to the canalicular membrane. Therefore, SR-BI, which is known to play a role in cholesterol uptake at the hepatocyte basolateral membrane, may also be involved in biliary cholesterol excretion. Based on these findings, a model is proposed in which local canalicular membrane PC biosynthesis in concert with the phospholipid transporter mdr2 and SR-BI, promotes the excretion of phospholipid and cholesterol into the bile.

  • plasma homocysteine is regulated by phospholipid methylation
    Journal of Biological Chemistry, 2003
    Co-Authors: Anna A Noga, Lori M Stead, Margaret E Brosnan, John T Brosnan, Yang Zhao, Dennis E. Vance
    Abstract:

    Abstract Mild hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Homocysteine, a non-protein amino acid, is formed fromS-adenosylhomocysteine and partially secreted into plasma. A potential source for homocysteine is methylation of the lipid Phosphatidylethanolamine to phosphatidylcholine by Phosphatidylethanolamine N-methyltransferase in the liver. We show that mice that lack PhosphatidylethanolamineN-methyltransferase have plasma levels of homocysteine that are ∼50% of those in wild-type mice. Hepatocytes isolated from methyltransferase-deficient mice secrete ∼50% less homocysteine. Rat hepatoma cells transfected with PhosphatidylethanolamineN-methyltransferase secrete more homocysteine than wild-type cells. Thus, PhosphatidylethanolamineN-methyltransferase is an important source of plasma homocysteine and a potential therapeutic target for hyperhomocysteinemia.

  • Plasma homocysteine is regulated by phospholipid methylation.
    The Journal of biological chemistry, 2002
    Co-Authors: Anna A Noga, Lori M Stead, Margaret E Brosnan, John T Brosnan, Yang Zhao, Dennis E. Vance
    Abstract:

    Mild hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Homocysteine, a non-protein amino acid, is formed from S-adenosylhomocysteine and partially secreted into plasma. A potential source for homocysteine is methylation of the lipid Phosphatidylethanolamine to phosphatidylcholine by Phosphatidylethanolamine N-methyltransferase in the liver. We show that mice that lack Phosphatidylethanolamine N-methyltransferase have plasma levels of homocysteine that are approximately 50% of those in wild-type mice. Hepatocytes isolated from methyltransferase-deficient mice secrete approximately 50% less homocysteine. Rat hepatoma cells transfected with Phosphatidylethanolamine N-methyltransferase secrete more homocysteine than wild-type cells. Thus, Phosphatidylethanolamine N-methyltransferase is an important source of plasma homocysteine and a potential therapeutic target for hyperhomocysteinemia.

  • biochemical and evolutionary significance of phospholipid methylation
    Journal of Biological Chemistry, 1998
    Co-Authors: Christopher J. Walkey, Liqing Yu, Luis B Agellon, Dennis E. Vance
    Abstract:

    Abstract All nucleated mammalian cells synthesize phosphatidylcholine from choline via the CDP-choline pathway. Hepatocytes have a second pathway for the synthesis of phosphatidylcholine, a stepwise methylation of Phosphatidylethanolamine, catalyzed by PhosphatidylethanolamineN-methyltransferase and encoded by the Pemptgene. We report that when Pempt-deficient mice were fed a choline-deficient diet for 3 days, severe liver pathology occurred apparently due to a lack of phosphatidylcholine biosynthesis. The hepatic concentration of phosphatidylcholine decreased by 50% compared with wild type mice on the diet. The levels of plasma triacylglycerols and cholesterol were decreased by greater than 90% in thePempt-deficient mice. We suggest that the Pemptgene has been maintained during evolution to provide phosphatidylcholine when dietary choline is insufficient, as might occur during starvation or pregnancy.

  • Phosphatidylethanolamine N-methyltransferase from liver.
    Biochimica et Biophysica Acta, 1997
    Co-Authors: Dennis E. Vance, Christopher J. Walkey, Zheng Cui
    Abstract:

    Phosphatidylethanolamine N-methyltransferase (PEMT) converts Phosphatidylethanolamine to phosphatidylcholine. Most PEMT activity (PEMT1) is associated with endoplasmic reticulum. A second form of the enzyme (PEMT2) has been localized to the mitochondria-associated membrane. PEMT2 is a 22.5-kDa protein that has been purified from rat liver. The rat liver PEMT2 cDNA and the murine PEMT gene have been cloned and characterized. The PEMT gene encodes both forms of the enzyme. Deletion of the PEMT gene eliminates all activity in liver that converts Phosphatidylethanolamine to phosphatidylcholine. The activity of PEMT is regulated by supply of the substrates, Phosphatidylethanolamine and S-adenosylmethionine, and by the product S-adenosylhomocysteine. The expression of the gene is regulated during development and by the supply of choline in the diet. There is reciprocal regulation of the Kennedy pathway for phosphatidylcholine biosynthesis (via CDP-choline) and Phosphatidylethanolamine N-methyltransferase. Several experimental approaches suggest that this enzyme might play a role in regulation of hepatocyte growth and cell division.

Zheng Cui - One of the best experts on this subject based on the ideXlab platform.

  • Phosphatidylethanolamine N-methyltransferase from liver.
    Biochimica et Biophysica Acta, 1997
    Co-Authors: Dennis E. Vance, Christopher J. Walkey, Zheng Cui
    Abstract:

    Phosphatidylethanolamine N-methyltransferase (PEMT) converts Phosphatidylethanolamine to phosphatidylcholine. Most PEMT activity (PEMT1) is associated with endoplasmic reticulum. A second form of the enzyme (PEMT2) has been localized to the mitochondria-associated membrane. PEMT2 is a 22.5-kDa protein that has been purified from rat liver. The rat liver PEMT2 cDNA and the murine PEMT gene have been cloned and characterized. The PEMT gene encodes both forms of the enzyme. Deletion of the PEMT gene eliminates all activity in liver that converts Phosphatidylethanolamine to phosphatidylcholine. The activity of PEMT is regulated by supply of the substrates, Phosphatidylethanolamine and S-adenosylmethionine, and by the product S-adenosylhomocysteine. The expression of the gene is regulated during development and by the supply of choline in the diet. There is reciprocal regulation of the Kennedy pathway for phosphatidylcholine biosynthesis (via CDP-choline) and Phosphatidylethanolamine N-methyltransferase. Several experimental approaches suggest that this enzyme might play a role in regulation of hepatocyte growth and cell division.

Gottfried Pohlentz - One of the best experts on this subject based on the ideXlab platform.

  • neoglycolipids derived from Phosphatidylethanolamine serve as probes in cell culture studies on glycolipid metabolism
    Biological Chemistry, 2000
    Co-Authors: Gottfried Pohlentz, Brigitte Drees
    Abstract:

    The neoglycolipid (NeoGL) N-acetyl-1-deoxy-1-phosphatidylethanolamino lacto-N-tetraositol [Lc4Ose-PtdEtn(NAc)] and the radioactivly labeled analog [Lc4Ose-PtdEtn(N[14C]Ac)] were synthesized by coupling the corresponding oligosaccharide to Phosphatidylethanolamine (dihexadecyl) via reductive amination and subsequent N-acetylation with unlabeled and [14C]acetic acid anhydride, respectively. Lc4Ose-PtdEtn(N[14C]Ac) was then incubated with homogenates of rat small intestine epithelial cells (IEC-6) at pH 4. The reaction products were shown to be the degradation products formed by glycosidases by fast atom bombardment mass spectrometry (FAB MS). On the other hand, incubation of Lc4Ose-PtdEtn(NAc) with IEC-6 cell homogenates in sialyltransferase assays yielded the corresponding sialylated product. When Lc4Ose-PtdEtn(N[14C]Ac) was fed to IEC-6 cells as BSA complex, up to 5% of the NeoGL administered were taken up by the cells. After extraction of the NeoGL and separation by thin layer chromatography (TLC) the catabolic products Lc3Ose-PtdEtn(N[14C]Ac), Lac-PtdEtn(N[14C]Ac), and Glc-PtdEtn(N[14C]Ac), as well as the main anabolic product NeuGc-Lc4Ose-PtdEtn(N[14C]Ac) could be identified by FAB MS. These results demonstrate that PtdEtn-derived NeoGL can be used as probes for studies on the metabolism of specific oligosaccharide structures in cell culture.

  • Neoglycolipids of 1-deoxy-1-phosphatidylethanolaminolactitol type: synthesis, structure analysis, and use as probes for characterization of glycosyltransferases.
    Methods in enzymology, 1994
    Co-Authors: Gottfried Pohlentz, Heinz Egge
    Abstract:

    Publisher Summary Neoglycolipids (NeoGL) of the 1-deoxy- 1-phosphatidylethanolamino-lactitol type (Lac-PtdEtn), synthesized by coupling an oligosaccharide to Phosphatidylethanolamine (PtdEtn) by reductive amination, have been used for studies on antigenicity, receptor function, and lectin and toxin binding by carbohydrates. Glycosyl-PtdEtns and especially the N-acetylated derivatives can serve as acceptors for glycosphingolipid (GSL) glycosyltransferases. The NeoGLs are as good acceptors as the authentic GSL analogs, and they are glycosylated by the same enzymes. This chapter describes an improved synthesis of Lac-PtdEtn-type neoglycolipids, their N-acetylation, and their use as acceptors for glycosyl-transferases and for structure elucidation of oligosaccharides by fast atom bombardment-mass spectrometry (FAB-MS). Radiolabeled NeoGL can be useful tools for investigations on glycolipid metabolism in cell culture. For the glycosyl-PtdEtn compounds to serve as substitutes for natural GSL in glycosyltransferase assays, it must be ascertained that neoglycolipids are converted to the analogous products by the same enzymes that act on natural GSL and that they exhibit similar apparent kinetic constants. This chapter illustrates the use of glycosyl-PtdEtns and the N-acetylated derivatives as acceptors for sialyltransferases from rat liver Golgi and discusses the transferase products by FAB-MS. By competition experiments it is demonstrated that the NeoGL and the authentic GSL analog are sialylated by the same respective enzymes.

Ulla Lahtinen - One of the best experts on this subject based on the ideXlab platform.

  • mass spectrometric analysis reveals changes in phospholipid neutral sphingolipid and sulfatide molecular species in progressive epilepsy with mental retardation epmr brain a case study
    Journal of Neurochemistry, 2005
    Co-Authors: Martin Hermansson, Pentti Somerharju, Reijo Kakela, Maria Berghall, Annaelina Lehesjoki, Ulla Lahtinen
    Abstract:

    Progressive epilepsy with mental retardation, EPMR, belongs to a group of inherited neurodegenerative disorders, the neuronal ceroid lipofuscinoses. The CLN8 gene that underlies EPMR encodes a novel transmembrane protein that localizes to the endoplasmic reticulum (ER) and ER–Golgi intermediate compartment. Recently, CLN8 was linked to a large eukaryotic protein family of TLC (TRAM, Lag1, CLN8) domain homologues with postulated functions in lipid synthesis, transport or sensing. By using liquid chromatography/mass spectrometry we analysed molecular species of major phosholipid and simple sphingolipid classes from cerebral samples of two EPMR patients representing a progressive and advanced state of the disease. The progressive state brain showed reduced levels of ceramide, galactosyl- and lactosylceramide and sulfatide as well as a decrease in long fatty acyl chain containing molecular species within these classes. Among glycerophospholipid classes, an increase in species containing polyunsaturated acyl chains was detected especially in phosphatidylserines and Phosphatidylethanolamines. By contrast, saturated and monounsaturated species were overrepresented among phosphatidylserine, Phosphatidylethanolamine and phosphatidylinositol classes in the advanced state sample. The observed changes in brain sphingo- and phospholipid molecular profiles may result in altered membrane stability, lipid peroxidation, vesicular trafficking or neurotransmission and thus may contribute to the progression of the molecular pathogenesis of EPMR.

Christopher J. Walkey - One of the best experts on this subject based on the ideXlab platform.

  • biochemical and evolutionary significance of phospholipid methylation
    Journal of Biological Chemistry, 1998
    Co-Authors: Christopher J. Walkey, Liqing Yu, Luis B Agellon, Dennis E. Vance
    Abstract:

    Abstract All nucleated mammalian cells synthesize phosphatidylcholine from choline via the CDP-choline pathway. Hepatocytes have a second pathway for the synthesis of phosphatidylcholine, a stepwise methylation of Phosphatidylethanolamine, catalyzed by PhosphatidylethanolamineN-methyltransferase and encoded by the Pemptgene. We report that when Pempt-deficient mice were fed a choline-deficient diet for 3 days, severe liver pathology occurred apparently due to a lack of phosphatidylcholine biosynthesis. The hepatic concentration of phosphatidylcholine decreased by 50% compared with wild type mice on the diet. The levels of plasma triacylglycerols and cholesterol were decreased by greater than 90% in thePempt-deficient mice. We suggest that the Pemptgene has been maintained during evolution to provide phosphatidylcholine when dietary choline is insufficient, as might occur during starvation or pregnancy.

  • Phosphatidylethanolamine N-methyltransferase from liver.
    Biochimica et Biophysica Acta, 1997
    Co-Authors: Dennis E. Vance, Christopher J. Walkey, Zheng Cui
    Abstract:

    Phosphatidylethanolamine N-methyltransferase (PEMT) converts Phosphatidylethanolamine to phosphatidylcholine. Most PEMT activity (PEMT1) is associated with endoplasmic reticulum. A second form of the enzyme (PEMT2) has been localized to the mitochondria-associated membrane. PEMT2 is a 22.5-kDa protein that has been purified from rat liver. The rat liver PEMT2 cDNA and the murine PEMT gene have been cloned and characterized. The PEMT gene encodes both forms of the enzyme. Deletion of the PEMT gene eliminates all activity in liver that converts Phosphatidylethanolamine to phosphatidylcholine. The activity of PEMT is regulated by supply of the substrates, Phosphatidylethanolamine and S-adenosylmethionine, and by the product S-adenosylhomocysteine. The expression of the gene is regulated during development and by the supply of choline in the diet. There is reciprocal regulation of the Kennedy pathway for phosphatidylcholine biosynthesis (via CDP-choline) and Phosphatidylethanolamine N-methyltransferase. Several experimental approaches suggest that this enzyme might play a role in regulation of hepatocyte growth and cell division.