Marie Zarevúcka

The enzymatic regioselective monopalmitoylation of racemic 9-(2,3-dihydroxypropyl)- adenine (DHPA), an approved antiviral agent, has been performed by an immobilized form of Candida antarctica B lipase (CAL-B) using a 4:1 DMF/hexane mixture as the reaction medium. To improve the chemical yield of the desired monopalmitoylation reaction, solid-phase chemical modifications of the lipase were evaluated. The reaction yield was successfully increased obtaining 100% product after a second treatment of the product solution with fresh immobilised chemically glycosylated-CAL-B.

Buff‐tailed bumblebees, Bombus terrestris, use a male sex pheromone for premating communication. Its main component is a sesquiterpene, 2,3‐dihydrofarnesol. This paper reports the isolation of a thiolase (acetyl‐CoA thiolase, AACT_BT), the first enzyme involved in the biosynthetic pathway leading to formation of isoprenoids in the B. terrestris male sex pheromone. Characterisation of AACT_BT might contribute to a better understanding of pheromonogenesis in the labial gland of B. terrestris males. The protein was purified to apparent homogeneity by column chromatography with subsequent stepwise treatment. AACT_BT showed optimum acetyltransferase activity at pH 7.1 and was strongly inhibited by iodoacetamide. The enzyme migrated as a band with an apparent mass of 42.9 kDa on SDS‐PAGE. MS analysis of an AACT_BT tryptic digest revealed high homology to representatives of the thiolase family. AACT_BT has 96 % amino acid sequence identity with the previously reported Bombus impatiens thiolase.

The thermal and solvent tolerance of enzymes is highly important for their industrial use. We show here that the enzyme lipase from Rhizopus oryzae exhibits exceptionally high thermal stability and high solvent tolerance and even increased activity in acetone when immobilized onto a graphene oxide (GO) nanosupport prepared by Staudenmaier and Brodie methods. We studied various forms of immobilization of the enzyme: by physical adsorption, covalent attachment, and additional crosslinking. The activity recovery was shown to be dependent on the support type, enzyme loading and immobilization procedure. Covalently immobilized lipase showed significantly better resistance to heat inactivation (the activity recovery was 65% at 70 °C) in comparison with the soluble counterpart (the activity recovery was 65% at 40 °C). Physically adsorbed lipase achieved over 100% of the initial activity in a series of organic solvents. These findings, showing enhanced thermal stability and solvent tolerance of graphene oxide immobilized enzyme, will have a profound impact on practical industrial scale uses of enzymes for the conversion of lipids into fuels.

In addition to their general role in the hydrolysis of storage lipids, bumblebee lipases can participate in the biosynthesis of fatty acids that serve as precursors of pheromones used for sexual communication. We studied the temporal dynamics of lipolytic activity in crude extracts from the cephalic part of Bombus terrestris labial glands. Extracts from 3-day-old males displayed the highest lipolytic activity. The highest lipase gene expression level was observed in freshly emerged bumblebees, and both gene expression and lipase activity were lower in bumblebees older than 3 days. Lipase was purified from labial glands, further characterized and named as BT-1. The B. terrestris orthologue shares 88% sequence identity with B. impatiens lipase HA. The molecular weight of B. terrestris lipase BT-1 was approximately 30 kDa, the pH optimum was 8.3, and the temperature optimum was 50°C. Lipase BT-1 showed a notable preference for C8-C10 p-nitrophenyl esters, with the highest activity toward p-nitrophenyl caprylate (C8). The Michaelis constant (K_m) and maximum reaction rate (V_max) for p-nitrophenyl laurate hydrolysis were K_m = 0.0011 mM and V_max = 0.15 U/mg. This is the first report describing neutral lipase from the labial gland of B. terrestris. Our findings help increase understanding of its possible function in the labial gland.

Lipases from Geotrichum candidum 4013 (extracellular lipase and cell-bound lipase) were immobilized by adsorption on chitosan beads. The enzyme preparations were tested in the synthesis of ester prodrugs from racemic 9-(2,3-dihydroxypropyl)adenine in dimethylformamide with different vinyl esters (acetate, butyrate, decanoate, laurate, palmitate). The transesterification activities of these immobilized enzymes were compared with commercially available lipases (lipase from hog pancreas, Aspergillus niger, Candida antarctica, Pseudomonas fluorescens). Lipase from Candida antarctica was found to be the most efficient enzyme regarding chemical yield of the desired products, while transesterification by lipase from Aspergillus niger resulted in lower yields.

The fungus Geotrichum candidum 4013 produces two types of lipases (extracellular and cell‐bound). Both enzymes were tested for their hydrolytic ability to p‐nitrophenyl esters and compounds having a structure similar to the original substrate (triacylglycerols). Higher lipolytic activity of extracellular lipase was observed when triacylglycerols of medium‐ (C12) and long‐ (C18) chain fatty acids were used as substrates. Cell‐bound lipase preferentially hydrolysed trimyristate (C14). The differences in the abilities of these two enzymes to hydrolyse p‐nitrophenyl esters were observed as well. The order of extracellular lipase hydrolysis relation velocity was as follows: p‐nitrophenyl decanoate > p‐nitrophenyl caprylate > p‐nitrophenyl laurate > p‐nitrophenyl palmitate > p‐nitrophenyl stearate. The cell‐bound lipase indicates preference for p‐nitrophenyl palmitate. The most striking differences in the ratios between the activity of both lipases (extracellular : cell‐bound) towards different fatty acid methyl esters were 2.2 towards methyl hexanoate and 0.46 towards methyl stearate (C18). The Michaelis constant (K_m) and maximum reaction rate (V_max) for p‐nitrophenyl palmitate hydrolysis of cell‐bound lipase were significantly higher (K_m 2.462 mM and V_max 0.210 U/g/min) than those of extracellular lipase (K_m 0.406 mM and V_max 0.006 U/g/min). Copyright © 2010 John Wiley & Sons, Ltd.

Different types of enzymes such as lipases, several phosphatases, dehydrogenases, oxidases, amylases and others are well suited for the reactions in SC-CO₂. The stability and the activity of enzymes exposed to carbon dioxide under high pressure depend on enzyme species, water content in the solution and on the pressure and temperature of the reaction system. The three-dimensional structure of enzymes may be significantly altered under extreme conditions, causing their denaturation and consequent loss of activity. If the conditions are less adverse, the protein structure may be largely retained. Minor structural changes may induce an alternative active protein state with altered enzyme activity, specificity and stability.

Different plant products have been subjected to detailed investigations due to their increasing importance for improving human health. Plants are sources of many groups of natural products, of which large number of new compounds has already displayed their high impact in human medicine. This review deals with the natural products which may be found dissolved in lipid phase (phytosterols, vitamins etc.). Often subsequent convenient transformation of natural products may further improve the pharmacological properties of new potential medicaments based on natural products. To respect basic principles of sustainable and green procedures, enzymes are often employed as efficient natural catalysts in such plant product transformations. Transformations of lipids and other natural products under the conditions of enzyme catalysis show increasing importance in environmentally safe and sustainable production of pharmacologically important compounds. In this review, attention is focused on lipases, efficient and convenient biocatalysts for the enantio- and regioselective formation / hydrolysis of ester bond in a wide variety of both natural and unnatural substrates, including plant products, eg. plant oils and other natural lipid phase compounds. The application of enzymes for preparation of acylglycerols and transformation of other natural products provides big advantage in comparison with employing of conventional chemical methods: Increased selectivity, higher product purity and quality, energy conservation, elimination of heavy metal catalysts, and sustainability of the employed processes, which are catalyzed by enzymes. Two general procedures are used in the transformation of lipid-like natural products: (a) Hydrolysis/alcoholysis of triacylglycerols and (b) esterification of glycerol. The reactions can be performed under conventional conditions or in supercritical fluids/ionic liquids. Enzyme-catalyzed reactions in supercritical fluids combine the advantages of biocatalysts (substrate specificity under mild reaction conditions) and supercritical fluids (high mass-transfer rate, easy separation of reaction products from the solvent, environmental benefits based on excluding organic solvents from the production process).