Publications

• Acyl coenzyme A dependent retinol esterification by acyl coenzyme A: diacylglycerol acyltransferase 1.

  Orland M.D., Anwar K., Cromley D., Chu C.H., Chen L., Billheimer J.T., Hussain M.M., Cheng D.

  We provide biochemical evidence that enzymes involved in the synthesis of triacylglycerol, namely acyl coenzyme A:diacylglycerol acyltransferase (DGAT) and acyl coenzyme A:monoacylglycerol acyltransferase (MGAT), are capable of carrying out the acyl coenzyme A:retinol acyltransferase (ARAT) reacti ... >> More

  We provide biochemical evidence that enzymes involved in the synthesis of triacylglycerol, namely acyl coenzyme A:diacylglycerol acyltransferase (DGAT) and acyl coenzyme A:monoacylglycerol acyltransferase (MGAT), are capable of carrying out the acyl coenzyme A:retinol acyltransferase (ARAT) reaction. Among them, DGAT1 appears to have the highest specific activity. The apparent K(m) values of recombinant DGAT1/ARAT for retinol and palmitoyl coenzyme A were determined to be 25.9+/-2.1 microM and 13.9+/-0.3 microM, respectively, both of which are similar to the values previously determined for ARAT in native tissues. A novel selective DGAT1 inhibitor, XP620, inhibits recombinant DGAT1/ARAT at the retinol recognition site. In the differentiated Caco-2 cell membranes, XP620 inhibits approximately 85% of the Caco-2/ARAT activity indicating that DGAT1/ARAT may be the major source of ARAT activity in these cells. Of the two most abundant fatty acyl retinyl esters present in the intact differentiated Caco-2 cells, XP620 selectively inhibits retinyl-oleate formation without influencing the retinyl-palmitate formation. Using this inhibitor, we estimate that approximately 64% of total retinyl ester formation occurs via DGAT1/ARAT. These studies suggest that DGAT1/ARAT is the major enzyme involved in retinyl ester synthesis in Caco-2 cells. << Less

  Biochim. Biophys. Acta 1737:76-82(2005) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Retinol esterification by microsomes from the mucosa of human small intestine. Evidence for acyl-Coenzyme A retinol acyltransferase activity.

  Helgerud P., Petersen L.B., Norum K.R.

  The mechanism of the intestinal esterification of retinol has been obscure. Recently, an acyl-Coenzyme A (CoA):retinol acyltransferase (ARAT) was found in rat intestinal microsomes, and experiments were therefore conducted to determine whether a corresponding enzyme exists in human small intestine ... >> More

  The mechanism of the intestinal esterification of retinol has been obscure. Recently, an acyl-Coenzyme A (CoA):retinol acyltransferase (ARAT) was found in rat intestinal microsomes, and experiments were therefore conducted to determine whether a corresponding enzyme exists in human small intestine. When microsomes were incubated with [3H]retinol and palmitoyl-CoA, or retinol and [1-14C]palmitoyl-CoA, radioactive retinyl palmitate was formed as identified by alumina column chromatography and reverse-phase high-pressure liquid chromatography. Heating the microsomes for 30 min at 60 degrees C resulted in loss of activity. The esterification was negligible without exogenous acyl-CoA and markedly stimulated by palmitoyl-, oleoyl-, and stearoyl-CoA in concentrations up to 20 microM. The acyl-CoA was successfully replaced by an acyl-CoA generating system, but not by unactivated palmitate (2.5-200 microM). The assay was dependent on the presence of albumin with optimum activity at 2-10 mg/ml. The optimal retinol concentration was 20-30 microM and pH approximately 7.4. The esterifying activity was completely inhibited by 8 mM of taurocholate and to 90% by 1 mM of 5,5'-dithiobis(2-nitrobenzoic acid). Activity was found throughout the small intestine. In jejunum the rate of retinol esterification was: 3.44 +/-2.24 nmol [3H]retinyl ester formed . mg microsomal protein-1 . min-1 (mean +/-SD, n = 12). The corresponding activity in whole homogenates of biopsies were 1.17 +/-0.28 (n = 8). It is concluded that human small intestine contains a microsomal acyl-CoA:retinol acyltransferase. Due to its high activity in vitro this enzyme is likely to be responsible for the intestinal esterification of retinol. << Less

  J Clin Invest 71:747-753(1983) [PubMed] [EuropePMC]

• A human skin multifunctional O-acyltransferase that catalyzes the synthesis of acylglycerols, waxes, and retinyl esters.

  Yen C.-L.E., Brown C.H. IV, Monetti M., Farese R.V. Jr.

  Acyl-CoA-dependent O-acyltransferases catalyze reactions in which fatty acyl-CoAs are joined to acyl acceptors containing free hydroxyl groups to produce neutral lipids. In this report, we characterize a human multifunctional O-acyltransferase (designated MFAT) that belongs to the acyl-CoA:diacylg ... >> More

  Acyl-CoA-dependent O-acyltransferases catalyze reactions in which fatty acyl-CoAs are joined to acyl acceptors containing free hydroxyl groups to produce neutral lipids. In this report, we characterize a human multifunctional O-acyltransferase (designated MFAT) that belongs to the acyl-CoA:diacylglycerol acyltransferase 2/acyl-CoA:monoacylglycerol acyltransferase (MGAT) gene family and is highly expressed in the skin. Membranes of insect cells and homogenates of mammalian cells overexpressing MFAT exhibited significantly increased MGAT, acyl-CoA:fatty acyl alcohol acyltransferase (wax synthase), and acyl-CoA:retinol acyltransferase (ARAT) activities, which catalyze the synthesis of diacylglycerols, wax monoesters, and retinyl esters, respectively. Furthermore, when provided with the appropriate substrates, intact mammalian cells overexpressing MFAT accumulated more waxes and retinyl esters than control cells. We conclude that MFAT is a multifunctional acyltransferase that likely plays an important role in lipid metabolism in human skin. << Less

  J. Lipid Res. 46:2388-2397(2005) [PubMed] [EuropePMC]

  This publication is cited by 7 other entries.

• Acyl CoA:retinol acyltransferase (ARAT) activity is present in bovine retinal pigment epithelium.

  Kaschula C.H., Jin M.H., Desmond-Smith N.S., Travis G.H.

  Visual perception is mediated by a family of G protein-coupled receptors called the opsins. The light-absorbing chromophore in most opsins is 11-cis-retinaldehyde, which is isomerized to all-trans-retinaldehyde upon absorption of a photon. Restoration of light sensitivity to the photobleached opsi ... >> More

  Visual perception is mediated by a family of G protein-coupled receptors called the opsins. The light-absorbing chromophore in most opsins is 11-cis-retinaldehyde, which is isomerized to all-trans-retinaldehyde upon absorption of a photon. Restoration of light sensitivity to the photobleached opsin requires chemical re-isomerization of the chromophore. This is carried out by an enzymatic pathway called the visual cycle in retinal pigment epithelial cells. The isomerase in this pathway uses fatty-acyl esters of all-trans-retinol as substrate. A retinyl-ester synthase that produces these esters, called lecithin:retinol acyltransferase (LRAT), has been extensively characterized. Based on prior biochemical studies and the phenotype in lrat(-/-) knockout mice, it has been assumed that LRAT is the sole or dominant retinyl-ester synthase in the retinal pigment epithelium. Here we demonstrate the presence of a second ester synthase activity in these cells called acyl CoA:retinol acyltransferase (ARAT). We show that this activity uses palmitoyl coenzyme A as an acyl donor, unlike LRAT which uses phosphatidylcholine. Similar to LRAT, ARAT esterifies both all-trans-retinol and 11-cis-retinol. LRAT and ARAT are both potently inhibited by the retinyl-ester analog, all-trans-retinylbromoacetate, but only ARAT is inhibited by progesterone. Unexpectedly, the maximum turnover rate (V(max)) of ARAT was similar to that of LRAT. However, the Michaelis constant (K(M)) of ARAT was 10-fold higher than the K(M) of LRAT for all-trans-retinol. These observations suggest that ARAT may complement LRAT to provide additional retinyl-ester synthase activity under conditions of high all-trans-retinol. These conditions occur in the retina following exposure to bright light. << Less

  Exp Eye Res 82:111-121(2006) [PubMed] [EuropePMC]

• Retinol esterification by rat liver microsomes. Evidence for a fatty acyl coenzyme A: retinol acyltransferase.

  Ross A.C.

  To explore the nature of retinyl ester synthesis by liver microsomes, membranes prepared from rat or cat liver were incubated under various conditions with [3H] retinol dispersed in dimethyl sulfoxide. When [3H]retinol, buffer, and microsomes were incubated together (basal conditions), some [3H]re ... >> More

  To explore the nature of retinyl ester synthesis by liver microsomes, membranes prepared from rat or cat liver were incubated under various conditions with [3H] retinol dispersed in dimethyl sulfoxide. When [3H]retinol, buffer, and microsomes were incubated together (basal conditions), some [3H]retinol esterification was consistently observed. However, the rate of esterification could be increased 6-to 11-fold by addition of either palmitoyl-CoA (100 microM) or a fatty acyl CoA-generating system. To determine whether the fatty acid used to esterify [3H]retinol under basal conditions might be derived from an endogenous pool of fatty acyl-CoA associated with the microsomal preparation, microsomes were pretreated at pH 7.4 with 0.5 M hydroxylamine, a reagent that reacts with coenzyme A thioesters to form hydroxamates. This pretreatment reduced the basal reaction by 69%. However, hydroxylamine-treated microsomes still retained acyltransferase activity, as shown by a 24-to 40-fold increase in retinyl ester synthesis after addition of palmitoyl-CoA. When microsomes were incubated with both [3H]retinol and [14C]palmitoyl-CoA of known specific radioactivities, the ratio of 14C to 3H in newly synthesized retinyl palmitate was essentially equal to that of its putative substrates, indicating that [14C]palmitate did not undergo significant isotope dilution prior to acylation of [3H]retinol. These experiments provide direct evidence for retinol esterification catalyzed by a microsomal acyl-CoA:retinol acyltransferase and indirect evidence for a pool of fatty acyl-CoA in isolated liver microsomes that is available to react with [3H]retinol to form esterified retinol. << Less

  J Biol Chem 257:2453-2459(1982) [PubMed] [EuropePMC]