R. Julien

Bio: R. Julien is an academic researcher from University of Provence. The author has contributed to research in topics: Colipase & Lipase. The author has an hindex of 15, co-authored 20 publications receiving 802 citations.

Studies on the Effect of Bile Salt and Colipase on Enzymatic Lipolysis. Improved Method for the Determination of Pancreatic Lipase and Colipase

Abstract: The rate of hydrolysis of long chain triglycerides by pure bovine pancreatic lipase has been determined in the presence of variable amounts of bile salts and colipase. Cofactor-free lipase is strongly inhibited by sodium taurodesoxycholate and by mixed bovine bile salts at concentrations higher than the critical micellar concentration. Bile salt inhibited lipase is reactivated by the addition of bovine colipase. Gel filtration of pancreatic juice from several species (Cow, dog, pig) on Sephadex G 100 allows the separation of lipase from colipase. It is found that the enzyme catalyzed hydrolysis of long chain triglycerides by pancreatic lipase from one species is activated by the addition of colipase from other species. Studies on the activation of pancreatic lipase by colipase in the presence of bile salts allowed the re-evaluation of optimal conditions for the determination of lipase and the development of a procedure to assay colipase.

Inhibition of pancreatic and microbial lipases by proteins

Abstract: We have compared the effect of several proteins, including melittin, β-lactoglobulin A, serum albumin, ovalbumin and myoglobin, on the hydrolysis of tributyrin and triolein by upases from various origins. All proteins tested inactivate pancreatic lipase in absence of colipase and bile salt. Inhibition is not significantly reversed by colipase in absence of bile salt except in systems containing tributyrin and melittin or triolein and β-lactoglobulin A. In all other cases, activation of pancreatic lipase by colipase in presence of inhibitory protein requires the presence of bile salt. Lipase from Rhizopus delemar is also inhibited by the proteins that inactivate pancreatic lipase. In contrast, the activity of lipase from Rhizopus arrhizus is not affected by the proteins in the same concentration range. Inhibition of lipase activity by amphiphiles such as proteins or detergents appears to be a general phenomenon not directly related to a decrease in tension at the triacylglycerol-water interface. Inhibition could be the result of desorption of lipase from its substrate due to a change in interfacial quality.

Studies on the inhibition of pancreatic and microbial lipases by soybean proteins.

Abstract: A protein, molecular weight 70,000 that inhibits pancreatic lipase has been isolated from soybean seeds. Inhibition is not reversed by colipase unless bile salts are added to the assay system. Inhibitory properties of the purified protein are very similar to those of serum albumin or alpha-lactoglobulin. It has been confirmed that, during intestinal lipolysis of dietary fats, bile salts play an essential role for the activation of the lipase-colipase system in the presence of inhibitory proteins. The purified soybean lipase inhibitory protein was shown to be highly surface-active and able to penetrate monomolecular films of various glycerides and phospholipids at high surface pressure. Inhibition of pancreatic lipase by proteins is related to their capacity to interact with lipids and to modify the quality of the substrate-water interface. The protein isolated from soybeans inhibits pancreatic and Rh. delemar lipase in contrast to the Rh. arrhizus enzyme.

Horse pancreatic lipase. Interaction with colipase from various species.

Abstract: Horse pancreatic lipase has been purified from tissue homogenates. Molecular and catalytic properties of horse lipase are comparable to those of the pancreatic lipases previously isolated. Kinetic studies of the inhibition of horse lipase activity by bile salts and of reactivation by pure colipase from three species (horse, ox and pig) allowed to calculate the apparent dissociation constant (Kd) of the lipase-colipase complex in the presence of the substrate (triolein). Identical values of Kd were found in all three cases (Kd = 1.1 10(-9) M). These values are lower by several orders of magnitude than that published for the binding between lipase and colipase in the absence of substrate. Qualitative experiments show that the activation of horse lipase can be accomplished by rat, dog and chicken colipase as well. The interaction between lipase and colipase is enhanced when the complex is adsorbed at the lipid-water interface. This specific protein-protein interaction is preserved in heterologous mixtures using colipases from other animal species.

Pancreatic and microbial lipases: A comparison of the interaction of pancreatic colipase with lipases of various origins

Abstract: Conjugated bile salts inhibit the hydrolysis of triglycerides (TG) by the lipases fromRhizopus arrhizus andGeotrichum candidum. This occurs for detergent concentrations similar to those which suppress the action of mammalian pancreatic lipases upon the same substrates. However, in opposition with what is observed with the latter enzymes, the activity is not restored by the addition of pancreatic colipase. Both pancreatic andR. arrhizus lipases are inactivated at tributyrin/water interface, but only the first enzyme is protected against this surface denaturation by the pancreatic cofactor. These observations suggest that colipases synthesized in mammalian pancreas display specific interaction towards the lipases made by the same organ.

Bacterial lipases: an overview of production, purification and biochemical properties.

Abstract: Lipases, triacylglycerol hydrolases, are an important group of biotechnologically relevant enzymes and they find immense applications in food, dairy, detergent and pharmaceutical industries. Lipases are by and large produced from microbes and specifically bacterial lipases play a vital role in commercial ventures. Some important lipase-producing bacterial genera include Bacillus, Pseudomonas and Burkholderia. Lipases are generally produced on lipidic carbon, such as oils, fatty acids, glycerol or tweens in the presence of an organic nitrogen source. Bacterial lipases are mostly extracellular and are produced by submerged fermentation. The enzyme is most commonly purified by hydrophobic interaction chromatography, in addition to some modern approaches such as reverse micellar and aqueous two-phase systems. Most lipases can act in a wide range of pH and temperature, though alkaline bacterial lipases are more common. Lipases are serine hydrolases and have high stability in organic solvents. Besides these, some lipases exhibit chemo-, regio- and enantioselectivity. The latest trend in lipase research is the development of novel and improved lipases through molecular approaches such as directed evolution and exploring natural communities by the metagenomic approach.

Lipases at interfaces : a review

Abstract: Lipases are acyl hydrolases that play a key role in fat digestion by cleaving long-chain triglycerides into polar lipids Due to an opposite polarity between the enzyme (hydrophilic) and their substrates (lipophilic), lipase reaction occurs at the interface between the aqueous and the oil phases Hence, interfaces are the key spots for lipase biocatalysis and an appropriate site for modulating lipolysis Surprisingly enough, knowledge about the effects of the interfacial composition on lipase catalysis is still limited and only described by the term "interfacial quality" Recent systematic studies based on a biophysical approach allowed for the first time to show the effects of the interfacial microenvironment on lipase catalysis These studies demonstrate that lipase activity as a function of interfacial composition is more attributed to substrate inaccessibility rather than to enzyme denaturation or inactivation, as it is often hypothesized A detailed analysis of the interfacial properties of all compounds involved in triglyceride digestion revealed that lipolysis is a self-regulated reaction This feedback mechanism can be explored as a new avenue to control lipase catalysis To substantiate this hypothesis, oil hydrolysis in a model gastro-intestinal system was performed, which can be seen as an interfacial engineering approach to enzyme reactivity control The presented characterization of the interfacial composition and its consequences provide a new approach for the understanding of lipase reactions at interfaces with direct impact on biotechnological and health care applications

Structure of the pancreatic lipase-procolipase complex

Abstract: Interfacial adsorption of pancreatic lipase is strongly dependent on the physical chemical properties of the lipid surface. These properties are affected by amphiphiles such as phospholipids and bile salts. In the presence of such amphiphiles, lipase binding to the interface requires a protein cofactor, colipase. We obtained crystals of the pancreatic lipase-procolipase complex and solved the structure at 3.04 A resolution. Here we describe the structure of procolipase, which essentially consists of three 'fingers' and is topologically comparable to snake toxins. The tips of the fingers contain most of the hydrophobic amino acids and presumably form the interfacial binding site. Lipase binding occurs at the opposite side to this site and involves polar interactions. Determination of the three-dimensional structure of pancreatic lipase has revealed the presence of two domains: an amino-terminal domain, at residues 1-336 containing the active site and a carboxy-terminal domain at residues 337-449 (ref. 6). Procolipase binds exclusively to the C-terminal domain of lipase. No conformational change in the lipase molecule is induced by the binding of procolipase.

Present and future applications of lipases

Abstract: (1985). Present and Future Applications of Lipases. Biotechnology and Genetic Engineering Reviews: Vol. 3, No. 1, pp. 193-218.