The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Robert Verger - One of the best experts on this subject based on the ideXlab platform.
-
human pancreatic lipase related protein 2 is a galactolipase
Biochemistry, 2004Co-Authors: Barbara Sias, Dominique Lafont, Robert Verger, Francine Ferrato, Philippe Grandval, Paul Boullanger, Alain De Caro, B Leboeuf, Frederic CarriereAbstract:Human pancreatic lipase-related protein 2 (HPLRP2) was found to be expressed in the pancreas, but its biochemical properties were not investigated in detail. A recombinant HPLRP2 was produced in insect cells and the yeast Pichia pastoris and purified by cation exchange chromatography. Its substrate specificity was investigated using pH-stat and Monomolecular film techniques and various lipid substrates (triglycerides, diglycerides, phospholipids, and galactolipids). Lipase activity of HPLRP2 on trioctanoin was inhibited by bile salts and poorly restored by adding colipase. In vivo, HPLRP2 therefore seems unlikely to show any lipase activity on dietary fat. In human pancreatic lipase (HPL), residues R256, D257, Y267, and K268 are involved in the stabilization of the open conformation of the lid domain, which interacts with colipase. These residues are not conserved in HPLRP2. When the corresponding mutations (R256G, D257G, Y267F, and K268E) are introduced into HPL, the effects of colipase are drastically reduced in the presence of bile salts. This may explain why colipase has such weak effects on HPLRP2. HPLRP2 displayed a very low level of activity on phospholipid micelles and Monomolecular films. Its activity on monogalactosyldiglyceride Monomolecular film, which was much higher, was similar to the activity of guinea pig pancreatic lipase related-protein 2, which shows the highest galactolipase activity ever measured. The physiological role of HPLRP2 suggested by the present results is the digestion of galactolipids, the most abundant lipids occurring in plant cells, and therefore, in the vegetables that are part of the human diet.
-
surface fluorescence resonance energy transfer studies on interfacial adsorption of thermomyces humicola lanuginosa lipase using Monomolecular films of cis parinaric acid
Biopolymers, 2002Co-Authors: S Yapoudjian, Margarita G Ivanova, A Zenatti, Allan Svendsen, Wladimir Marine, Marc Sentis, Isabelle Douchet, Robert VergerAbstract:The fluorescence resonance energy transfer (FRET) technique was adapted to study the process whereby lipase is adsorbed to Monomolecular lipid films spread at the air–water interface. When cis-parinaric acid (cis-PnA) was spread over an aqueous subphase before the injection of sodium taurodeoxycholate (NaTDC) and Thermomyces lanuginosa lipase (TLL), no FRET was observed. Under these conditions, no adsorption of TLL was detected using an ELISA. In contrast, FRET occurred when cis-PnA was spread over an aqueous subphase containing NaTDC and TLL. The FRET signals observed were attributed to the interactions between the adsorbed TLL and the cis-PnA Monomolecular films. Comparisons between the fluorescence emission spectra corresponding to the bulk phase and the aspirated film, in the presence and absence of TLL, showed that cis-PnA was undetectable in the bulk phase. We concluded that the FRET originated from the interface and not from the bulk phase. Using surface FRET, we estimated that the surface excess of the catalytically inactive mutant, TLL(S146A), was 1.6 higher than that present in the wild-type TLL. This finding is in agreement with independent measurements of the surface excess of TLL and TLL(S146A) on Monomolecular films of cis-PnA. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 65: 121–128, 2002
-
surface properties of unsaturated non oxidized and oxidized free fatty acids spread as Monomolecular films at an argon water interface
Chemistry and Physics of Lipids, 2000Co-Authors: Abdelkarim Abousalham, Frederic Fotiadu, Gérard Buono, Robert VergerAbstract:Abstract The interfacial properties of Monomolecular films of stearic acid (SA) oleic acid (OA), linoleic acid (LA), ricinoleic acid (RA), 13(S)-hydroperoxyoctadeca-9Z,11E-dienoic acid (13-HPODE) and 13(S)-hydroxyoctadeca-9Z,11E-dienoic acid (13-HODE) were studied by recording the changes occurring in response to Monomolecular film compression in their surface pressure and surface potential at the argon/water interface. The oxidized free fatty acids are more expanded than the parent non-oxidized free fatty acids, reflecting a higher hydrophilic–lipophilic balance. The lift-off values of the molecular area of 13-HODE, 13-HPODE and RA were 68, 74 and 106 A2 molecule−1, respectively, as compared to 47 and 40 A2 molecule−1 in the case of LA and OA, respectively. Variations in the molecular orientation of free fatty acids can result in large changes in the dipole moment which are not accompanied by appreciable changes in the surface pressure. In the case of the oxidized free fatty acids, the spontaneous desorption into the aqueous phase was found to increase at increasing surface pressures. The desorption rates of OA and LA increased dramatically in the presence of β-cyclodextrin (β-CD); whereas the presence of β-CD only slightly increased the desorption rates of the oxidized free fatty acids.
-
hydrolysis of Monomolecular films of long chain phosphatidylcholine by phospholipase a2 in the presence of β cyclodextrin
Colloids and Surfaces B: Biointerfaces, 1996Co-Authors: M Ivanova, Tzvetanka Ivanova, Robert Verger, I PanaiotovAbstract:Abstract The desorption rates of Monomolecular films of oleic acid (OA) and lysophosphatidylcholine (lyso PC) at the air/water interface by water soluble β-cyclodextrin (β-CD) were studied. The desorption of OA and lyso PC involves the complexation of the single acyl chain into the β-CD cavity and the solubilization of the β-CD/OA or β-CD/lyso PC complex into the aqueous subphase, associated with a rapid decrease in the surface pressure. In the case of Monomolecular films of egg phosphatidylcholine (egg PC), 1,2-dihexadecanoyl- sn -glycero-3-phosphatidylcholine (DPPC); 1,2-di( cis -9-octadecenoyl)- sn -glycero-3-phosphatidycholine (DOPC), no detectable changes in the surface pressure occurred after β-CD injection into the subphase. The hydrolysis of medium and long chain PC Monomolecular films by phospholipase A 2 (PLA 2 ) was investigated in the absence of β-CD in the subphase. The considerable difference between the apparent kinetic constants was attributed to physical steps possibly involving molecular reorganization in the interface of long chain lipolytic products, associated with enzyme product inhibition. In the presence of β-CD in the subphase, the enzymatic hydrolysis of Monomolecular films of long chain PC was found to have kinetic constants which were comparable to those measured with medium chain lipids. Furthermore, comparisons between the desorption rates of the β-CD/lipolytic product complexes and the enzymatic hydrolysis rates of long chain PC, in the presence of β-CD in the aqueous subphase, showed that the rate limiting step is neither the formation of the β-CD/lipolytic product complexes nor their desorption into the water subphase but the hydrolysis of the PC Monomolecular films by PLA 2 . The presence of β-CD in the water subphase made it possible for the first time to perform kinetic measurements on the rates of hydrolysis of Monomolecular films long chain PC by PLA 2 .
-
kinetic behaviour of pancreatic lipase in five species using emulsions and Monomolecular films of synthetic glycerides
Biochimica et Biophysica Acta, 1995Co-Authors: Youssef Gargouri, Abderraouf Bensalah, Isabelle Douchet, Robert VergerAbstract:Abstract In the absence of colipase and bile salts, using tributyrin emulsions or Monomolecular films of dicaprin at low surface pressure, we observed that no significant lipase activity can be measured with Human Pancreatic Lipase (HuPL), Horse Pancreatic Lipase (HoPL) or Dog Pancreatic Lipase (DPL). Only Porcine Pancreatic Lipase (PPL) and recombinant Guinea Pig Pancreatic Lipase Related Protein of type 2 (r-GPL) hydrolyse pure tributyrin in the absence of any additive, as well as dicaprin films at low surface pressures. The former lipases may lack enzyme activity because of irreversible interfacial denaturation due to the high energy existing at the tributyrin/water interface and at the dicaprin film surface at low surface pressures. The enzyme denaturation cannot be reflected in the number of disulfide bridges, since all the pancreatic lipases tested here contain six disulfide bridges, but behaved very differently at interfaces. We propose to use the surface pressure threshold, as determined using the Monomolecular technique, as a criterion for classifying lipases in terms of their sensitivity to interfacial denaturation.
Frederic Carriere - One of the best experts on this subject based on the ideXlab platform.
-
galactolipase activity of talaromyces thermophilus lipase on galactolipid micelles Monomolecular films and uv absorbing surface coated substrate
Biochimica et Biophysica Acta, 2018Co-Authors: Ines Belhaj, Priscila Suttoortiz, Moulay Sahaka, Audric Rousset, Goetz Parsiegla, Sawsan Amara, Dominique Lafont, Hafedh Belghith, Frederic CarriereAbstract:Talaromyces thermophilus lipase (TTL) was found to hydrolyze monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) substrates presented in various forms to the enzyme. Different assay techniques were used for each substrate: pHstat with dioctanoyl galactolipid-bile salt mixed micelles, barostat with dilauroyl galactolipid Monomolecular films spread at the air-water interface, and UV absorption using a novel MGDG substrate containing α-eleostearic acid as chromophore and coated on microtiter plates. The kinetic properties of TTL were compared to those of the homologous lipase from Thermomyces lanuginosus (TLL), guinea pig pancreatic lipase-related protein 2 and Fusarium solani cutinase. TTL was found to be the most active galactolipase, with a higher activity on micelles than on Monomolecular films or surface-coated MGDG. Nevertheless, the UV absorption assay with coated MGDG was highly sensitive and allowed measuring significant activities with about 10 ng of enzymes, against 100 ng to 10 μg with the pHstat. TTL showed longer lag times than TLL for reaching steady state kinetics of hydrolysis with Monomolecular films or surface-coated MGDG. These findings and 3D-modelling of TTL based on the known structure of TLL pointed out to two phenylalanine to leucine substitutions in TTL, that could be responsible for its slower adsorption at lipid-water interface. TTL was found to be more active on MGDG than on DGDG using both galactolipid-bile salt mixed micelles and galactolipid Monomolecular films. These later experiments suggest that the second galactose on galactolipid polar head impairs the enzyme adsorption on its aggregated substrate.
-
human pancreatic lipase related protein 2 is a galactolipase
Biochemistry, 2004Co-Authors: Barbara Sias, Dominique Lafont, Robert Verger, Francine Ferrato, Philippe Grandval, Paul Boullanger, Alain De Caro, B Leboeuf, Frederic CarriereAbstract:Human pancreatic lipase-related protein 2 (HPLRP2) was found to be expressed in the pancreas, but its biochemical properties were not investigated in detail. A recombinant HPLRP2 was produced in insect cells and the yeast Pichia pastoris and purified by cation exchange chromatography. Its substrate specificity was investigated using pH-stat and Monomolecular film techniques and various lipid substrates (triglycerides, diglycerides, phospholipids, and galactolipids). Lipase activity of HPLRP2 on trioctanoin was inhibited by bile salts and poorly restored by adding colipase. In vivo, HPLRP2 therefore seems unlikely to show any lipase activity on dietary fat. In human pancreatic lipase (HPL), residues R256, D257, Y267, and K268 are involved in the stabilization of the open conformation of the lid domain, which interacts with colipase. These residues are not conserved in HPLRP2. When the corresponding mutations (R256G, D257G, Y267F, and K268E) are introduced into HPL, the effects of colipase are drastically reduced in the presence of bile salts. This may explain why colipase has such weak effects on HPLRP2. HPLRP2 displayed a very low level of activity on phospholipid micelles and Monomolecular films. Its activity on monogalactosyldiglyceride Monomolecular film, which was much higher, was similar to the activity of guinea pig pancreatic lipase related-protein 2, which shows the highest galactolipase activity ever measured. The physiological role of HPLRP2 suggested by the present results is the digestion of galactolipids, the most abundant lipids occurring in plant cells, and therefore, in the vegetables that are part of the human diet.
Jay H Lee - One of the best experts on this subject based on the ideXlab platform.
-
regularized maximum likelihood estimation of sparse stochastic Monomolecular biochemical reaction networks
Computers & Chemical Engineering, 2016Co-Authors: Hong Jang, Kwangki K Kim, Richard D Braatz, Bhushan R Gopaluni, Jay H LeeAbstract:Abstract A sparse parameter matrix estimation method is proposed for identifying a stochastic Monomolecular biochemical reaction network system. Identification of a reaction network can be achieved by estimating a sparse parameter matrix containing the reaction network structure and kinetics information. Stochastic dynamics of a biochemical reaction network system is usually modeled by a chemical master equation (CME) describing the time evolution of probability distributions for all possible states. This paper considers closed Monomolecular reaction systems for which an exact analytical solution of the corresponding chemical master equation can be derived. The estimation method presented in this paper incorporates the closed-form solution into a regularized maximum likelihood estimation (MLE) for which model complexity is penalized. A simulation result is provided to verify performance improvement of regularized MLE over least-square estimation (LSE), which is based on a deterministic mass-average model, in the case of a small population size.
-
regularized maximum likelihood estimation of sparse stochastic Monomolecular biochemical reaction networks
IFAC Proceedings Volumes, 2014Co-Authors: Ifac Fellow, Hong Jang, Kwangki K Kim, Jay H Lee, Richard D BraatzAbstract:Abstract A sparse parameter estimation method is proposed for identifying a stochastic Monomolecular biochemical reaction network system. Identification of a reaction network can be achieved by estimating a sparse parameter matrix containing the reaction network structure and kinetics information. Stochastic dynamics of a biochemical reaction network system is usually modeled by a chemical master equation, which is composed of several ordinary differential equations describing the time evolution of probability distributions for all possible states. This paper considers closed Monomolecular reaction systems for which an exact analytical solution of the corresponding chemical master equation is available. The estimation method presented in this paper incorporates the closed-form solution into a regularized maximum likelihood estimation (MLE) for which model complexity is penalized, whereas most of existing studies on sparse reaction network identification use deterministic models for regularized least-square estimation. A simulation result is provided to verify performance improvement of the presented regularized MLE over the least squares (LSE) based on a deterministic mass-average model in the case of a small population size. Improved reaction structure detection is achieved by adding a penalty term for l 1 regularization to the exact maximum likelihood function.
Hong Jang - One of the best experts on this subject based on the ideXlab platform.
-
regularized maximum likelihood estimation of sparse stochastic Monomolecular biochemical reaction networks
Computers & Chemical Engineering, 2016Co-Authors: Hong Jang, Kwangki K Kim, Richard D Braatz, Bhushan R Gopaluni, Jay H LeeAbstract:Abstract A sparse parameter matrix estimation method is proposed for identifying a stochastic Monomolecular biochemical reaction network system. Identification of a reaction network can be achieved by estimating a sparse parameter matrix containing the reaction network structure and kinetics information. Stochastic dynamics of a biochemical reaction network system is usually modeled by a chemical master equation (CME) describing the time evolution of probability distributions for all possible states. This paper considers closed Monomolecular reaction systems for which an exact analytical solution of the corresponding chemical master equation can be derived. The estimation method presented in this paper incorporates the closed-form solution into a regularized maximum likelihood estimation (MLE) for which model complexity is penalized. A simulation result is provided to verify performance improvement of regularized MLE over least-square estimation (LSE), which is based on a deterministic mass-average model, in the case of a small population size.
-
regularized maximum likelihood estimation of sparse stochastic Monomolecular biochemical reaction networks
IFAC Proceedings Volumes, 2014Co-Authors: Ifac Fellow, Hong Jang, Kwangki K Kim, Jay H Lee, Richard D BraatzAbstract:Abstract A sparse parameter estimation method is proposed for identifying a stochastic Monomolecular biochemical reaction network system. Identification of a reaction network can be achieved by estimating a sparse parameter matrix containing the reaction network structure and kinetics information. Stochastic dynamics of a biochemical reaction network system is usually modeled by a chemical master equation, which is composed of several ordinary differential equations describing the time evolution of probability distributions for all possible states. This paper considers closed Monomolecular reaction systems for which an exact analytical solution of the corresponding chemical master equation is available. The estimation method presented in this paper incorporates the closed-form solution into a regularized maximum likelihood estimation (MLE) for which model complexity is penalized, whereas most of existing studies on sparse reaction network identification use deterministic models for regularized least-square estimation. A simulation result is provided to verify performance improvement of the presented regularized MLE over the least squares (LSE) based on a deterministic mass-average model in the case of a small population size. Improved reaction structure detection is achieved by adding a penalty term for l 1 regularization to the exact maximum likelihood function.
Richard D Braatz - One of the best experts on this subject based on the ideXlab platform.
-
regularized maximum likelihood estimation of sparse stochastic Monomolecular biochemical reaction networks
Computers & Chemical Engineering, 2016Co-Authors: Hong Jang, Kwangki K Kim, Richard D Braatz, Bhushan R Gopaluni, Jay H LeeAbstract:Abstract A sparse parameter matrix estimation method is proposed for identifying a stochastic Monomolecular biochemical reaction network system. Identification of a reaction network can be achieved by estimating a sparse parameter matrix containing the reaction network structure and kinetics information. Stochastic dynamics of a biochemical reaction network system is usually modeled by a chemical master equation (CME) describing the time evolution of probability distributions for all possible states. This paper considers closed Monomolecular reaction systems for which an exact analytical solution of the corresponding chemical master equation can be derived. The estimation method presented in this paper incorporates the closed-form solution into a regularized maximum likelihood estimation (MLE) for which model complexity is penalized. A simulation result is provided to verify performance improvement of regularized MLE over least-square estimation (LSE), which is based on a deterministic mass-average model, in the case of a small population size.
-
regularized maximum likelihood estimation of sparse stochastic Monomolecular biochemical reaction networks
IFAC Proceedings Volumes, 2014Co-Authors: Ifac Fellow, Hong Jang, Kwangki K Kim, Jay H Lee, Richard D BraatzAbstract:Abstract A sparse parameter estimation method is proposed for identifying a stochastic Monomolecular biochemical reaction network system. Identification of a reaction network can be achieved by estimating a sparse parameter matrix containing the reaction network structure and kinetics information. Stochastic dynamics of a biochemical reaction network system is usually modeled by a chemical master equation, which is composed of several ordinary differential equations describing the time evolution of probability distributions for all possible states. This paper considers closed Monomolecular reaction systems for which an exact analytical solution of the corresponding chemical master equation is available. The estimation method presented in this paper incorporates the closed-form solution into a regularized maximum likelihood estimation (MLE) for which model complexity is penalized, whereas most of existing studies on sparse reaction network identification use deterministic models for regularized least-square estimation. A simulation result is provided to verify performance improvement of the presented regularized MLE over the least squares (LSE) based on a deterministic mass-average model in the case of a small population size. Improved reaction structure detection is achieved by adding a penalty term for l 1 regularization to the exact maximum likelihood function.
