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Lipases

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Lipases (triacylglycerol acyl hydrolases; EC 3.1.1.3) are hydrolases that act upon aqueous conditions, and target the carboxyl ester bonds present in triacylglycerols to produce fatty acids and glycerol. The unique ability of the lipases to carry out the reverse reaction, leading to esterification, alcoholysis and acidolysis is carried out in non-aqueous solutions 1. Furthermore, lipases are excellent examples of ”promiscuous” enzymes, catalyzing reactions quite different from the above, like racemisation and epoxidation 2.
These above specific chemical transformations performed by lipases, has turned them increasingly popular in food, detergent, cosmetic, organic synthesis, and pharmaceutical industries 3. Lipases are ubiquitous in nature and are expressed by several microorganisms, namely bacteria, yeasts and fungi, as well as animals and plants 1, 3, 4. Those of microbial origin, represent the most widely used enzymes in biotechnological applications and organic chemistry 5, 6. There are two types of lipases, accordingly to their cell distribution: (i) extracellular lipases, which are secreted into culture broth and (ii) intracellular or whole cell lipases, which located either inside the cell or in the cell-wall 7. Due to their easy recovery, extracellular enzymes have been extensively studied and commercialized comparing to intracellular 1, 3, 4. On the other hand, whole-cell biocatalysts have several advantages on an industrial point of view when compared to the free extracellular enzymes, because as naturally immobilized enzymes, they can be used in continuous or repeated processes. Besides, the direct utilization of the biomass as biocatalyst would avoid further time-consuming costly purification and immobilization steps 8.
Microalgae are sunlight-driven green cell factories for the production of value-added products such as lipids, carbohydrates, proteins, and pigments 9. Nannochloropsis species are unicellular photosynthetic heterokonts and inhabit a wide range of marine and freshwater ecosystems, indicating their diversity. Nannochloropsis has been of commercial interest because of its promising characteristics such as high triacyl-glycerol (TAG) content, synthesis of economically valuable by-products and higher growth rate. Vieller et al., 10 probed the N. oceanica CCMP1779 genome for lipase-encoding genes with sequence similar to those of Saccharomyces cerevisiae and Chlamydomonas and a total of 52 putative lipase encoding genes were retrieved. Transcriptome studies in N. oceanica revealed that under N stress, several lipases were highly stimulated and had putative functions in recycling fatty acids (FA) from membrane lipids for TAG formation 11.
Given the importance of characterizing lipolytic activities from new sources and the advantages of membrane-bound lipases over intracellular or extracellular counterparts, the main objective of the present work was to characterize a membrane-bound lipolytic enzyme (MBL-Enzyme) in hydrolytic reactions, determine its stability in various organic solvents and finally evaluate its synthetic activity in esterification reactions.

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