Water activity and substrate concentration effects on lipase activity

Water will Find Its Way: Transport through Narrow Tunnels in Hydrolases

An aqueous environment is vital for life as we know it, and water is essential for nearly all biochemical processes at the molecular level. Proteins utilize water molecules in various ways. Consequently, proteins must transport water molecules across their internal network of tunnels to reach the desired action sites, either within them or by functioning as molecular pipes to control cellular osmotic pressure. Despite water playing a crucial role in enzymatic activity and stability, its transport has been largely overlooked, with studies primarily focusing on water transport across membrane proteins. The transport of molecules through a protein's tunnel network is challenging to study experimentally, making molecular dynamics simulations the most popular approach for investigating such events. In this study, we focused on the transport of water molecules across three different α/β-hydrolases: haloalkane dehalogenase, epoxide hydrolase, and lipase. Using a 5 μs adaptive simulation per system, we observed that only a few tunnels were responsible for the majority of water transport in dehalogenase, in contrast to a higher diversity of tunnels in other enzymes. Interestingly, water molecules could traverse narrow tunnels with subangstrom bottlenecks, which is surprising given the commonly accepted water molecule radius of 1.4 Å. Our analysis of the transport events in such narrow tunnels revealed a markedly increased number of hydrogen bonds formed between the water molecules and protein, likely compensating for the steric penalty of the process. Overall, these commonly disregarded narrow tunnels accounted for ∼20% of the total water transport observed, emphasizing the need to surpass the standard geometrical limits on the functional tunnels to properly account for the relevant transport processes. Finally, we demonstrated how the obtained insights could be applied to explain the differences in a mutant of the human soluble epoxide hydrolase associated with a higher incidence of ischemic stroke.

Effects of kosmotropic, chaotropic, and neutral salts on Candida antarctica B lipase: An analysis of the secondary structure and its hydrolytic activity on triglycerides

The effects of different concentrations of Hofmeister salts on the hydrolytic activity on triglycerides and the secondary structure of lipase B from Candida antarctica (CALB) were investigated. Structural changes after short- and long-time incubation at high salt concentrations were determined using circular dichroism (CD), fluorescence, and RMSD-RMSF simulations. At 5.2 M NaCl, the hydrolytic activity of CALB on tributyrin (TC4) and trioctanoin (TC8) was enhanced by 1.5 (from 817 ± 3.9 to 1228 ± 4.3 U/mg)- and 8.7 (from 25 ± 0.3 to 218 ± 2.3 U/mg)-folds compared with 0.15 M NaCl, respectively at pH 7.0 and 40 °C. An activity activation was seen with other salts tested; however, long-time incubation (24 h) did not result in retention of the activation effect for any of the salts tested. Secondary structure CD and fluorescence spectra showed that long-time incubation with NaCl, KCl, and CsCl provokes a compact structure without loss of native conformation, whereas chaotropic LiCl and CaCl2 induced an increase in the α-helical content, and kosmotropic Na2SO4 provoked a molten globule state with rich β-sheet content. The RMSD-RMSF simulation agreed with the CD analysis, highlighting a principal salt-induced effect at the α-helix 5 region, promoting two different conformational states (open and closed) depending on the type and concentration of salt. Lastly, an increase in the interfacial tension occurred when high salt concentrations were added to the reaction media, affecting the catalytic properties. The results indicate that high-salt environments, such as 2-5.2 M NaCl, can be used to increase the lipolytic activity of CALB on TC4 and TC8.

Stabilization of Rice Bran by Infrared Radiation Heating for Increased Resilience and Quality of Rice Bran Oil Production

Rice bran, a by-product of rice milling, is a valuable source of rice bran oil (RBO). However, it is prone to rancidity and must be processed quickly after rice polishing. The researchers found that rice bran stabilization with infrared radiation (IR) at 125 V and 135 V for 5∼10 min. The most promising IR treatments were 125 V for 10 min and 135 V for 5 min, which resulted in the lowest lipase activity (93∼96% inhibition) and levels of γ-oryzanol and α-tocopherol comparable to those of the untreated control. However, the color of rice bran and RBO based on L*, a*, b*, and total color difference (ΔE) and Gardner-20 mm index darkened. Upon storage of rice bran at 38°C for 8 weeks, the use of these two IR treatments completely inhibited the rise in free fatty acid (FFA) content and peroxide values throughout the storage period. In contrast, the control had a pre-storage FFA more than double that of IR-stabilized rice bran, which further increased during storage and, in the 8th week, was more than 6-fold higher than the pre-storage level. γ-oryzanol and α-tocopherol slightly decreased with storage and their levels did not differ between stabilized and unstabilized rice bran. RBO color darkening was again observed, but the color lightened with storage, especially upon treatment at 135 V for 5 min. In contrast, the color of control RBO darkened with storage. Thus, IR at 135 V for 5 min was the most promising method for rice bran stabilization, based on which commercial IR treatment instruments can be developed.

The Recent Advances in the Utility of Microbial Lipases: A Review

Lipases are versatile biocatalysts and are used in different bioconversion reactions. Microbial lipases are currently attracting a great amount of attention due to the rapid advancement of enzyme technology and its practical application in a variety of industrial processes. The current review provides updated information on the different sources of microbial lipases, such as fungi, bacteria, and yeast, their classical and modern purification techniques, including precipitation and chromatographic separation, the immunopurification technique, the reversed micellar system, aqueous two-phase system (ATPS), aqueous two-phase flotation (ATPF), and the use of microbial lipases in different industries, e.g., the food, textile, leather, cosmetics, paper, and detergent industries. Furthermore, the article provides a critical analysis of lipase-producing microbes, distinguished from the previously published reviews, and illustrates the use of lipases in biosensors, biodiesel production, and tea processing, and their role in bioremediation and racemization.

Sustainable Castor Bean Biodiesel Through Ricinus communis L. Lipase Extract Catalysis

The rise in oil prices, global warming, and the depletion of nonrenewable resources have led researchers to study sustainable alternatives to increasing energy demand. The autocatalysis from castor oil and castor lipases to produce biodiesel can be an excellent alternative to reduce the production costs and avoid the drawbacks of chemical transesterification. This study aimed to evaluate the catalytic activity of castor bean lipase extract (CBLE) on three vegetable oils hydrolysis, to obtain and enhance biodiesel yield by an autocatalysis from castor oil and CBLE. Furthermore, the enzymatic biodiesel physicochemical quality was analyzed. The enzymatic activity for olive oil was 76.12 U, 90.06 U for commercial castor oil, and 75.60 U in raw castor oil. The hydrolysis percentages were high at 25 °C, pH 4.5, for 4 h with 97.18% for olive oil, 98.86%, and 96.19% for commercial and raw castor oil, respectively. The CBLE catalyzed the transesterification reaction on castor oil to obtain 82.91% biodiesel yield under the selected conditions of 20% lipase loading, 1:6 oil/methanol molar ratio, and 10% buffer pH 4.5, 37 °C for 8 h. The castor biodiesel quality satisfied the ASTM-D6751 (USA) and EN-14214 (European Union) values, except for the density, viscosity, and moisture, as expected for this kind of biodiesel.

Comprehensive Composition of Flavor Precursors in Kopi Luwak and Jacu Exotic Green Bioprocessed Coffees

Exotic coffees may be defined as extravagant and unique coffees, primarily due to their production mode, including unusual bioprocessing or fermentation conditions associated with superior sensorial characteristics. The aim of the present study was to investigate the influence of bioprocessing and of growing conditions on flavor precursors of Jacu and Kopi Luwak exotic green coffees, respectively. Moreover, this is the first study to perform a detailed chemical analysis of these exotic coffees. Thirteen green Coffea arabica bean samples were obtained, five from Espírito Santo state, Brazil, and eight Kopi Luwak from different regions of Indonesia. Samples were analyzed regarding their proximate composition, chlorogenic acids (CGA), sucrose, alkaloids, triacylglycerols (TAG), diacylglycerols, free fatty acids, sterols, diterpenes and tocopherols. Scanning electron micrography confirmed bioprocessing of Jacu and Kopi Luwak coffee samples. Bioprocessing by the Jacu bird caused reductions of 69 and 28% in caffeine and CGA contents, respectively. The TAG profile of Jacu coffee was modified. TAG containing two saturated fatty acids were preferably hydrolyzed in detriment to those containing two unsaturated fatty acids. Other coffee components were not affected by the bird's digestion of the beans. Kopi Luwak coffee samples had a chemical composition in accordance with reported ranges for non-bioprocessed green C. arabica samples, except for caffeine (0.48 g/100 g) and CGA (5.09 g/100 g), which were found in low amounts. Crop year rather than location or post-harvest processing discriminated Kopi Luwak coffee samples, suggesting that weather conditions would be the most crucial aspect for their chemical composition, especially in terms of total lipids, ashes, total CGA, sucrose and proteins.

Biocatalytic Approach for Direct Esterification of Ibuprofen with Sorbitol in Biphasic Media

Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) introduced in the 1960s and widely used as an analgesic, anti-inflammatory, and antipyretic. In its acid form, the solubility of 21 mg/L greatly limits its bioavailability. Since the bioavailability of a drug product plays a critical role in the design of oral administration dosage, this study investigated the enzymatic esterification of ibuprofen as a strategy for hydrophilization. This work proposes an enzymatic strategy for the covalent attack of highly hydrophilic molecules using acidic functions of commercially available bioactive compounds. The poorly water-soluble drug ibuprofen was esterified in a hexane/water biphasic system by direct esterification with sorbitol using the cheap biocatalyst porcine pancreas lipase (PPL), which demonstrated itself to be a suitable enzyme for the effective production of the IBU-sorbitol ester. This work reports the optimization of the esterification reaction.

Enzymatic Synthesis of a Diene Ester Monomer Derived from Renewable Resource

The total or partial substitution of fossil raw materials by biobased materials from renewable resources is one of the great challenges of our society. In this context, the reaction under mild condition as enzyme-catalyzed esterification was applied to investigate the esterification of the biobased 10-undecenoic acid with 2-hydroxyethyl methacrylate (HEMA) to obtain a new diene ester monomer. The environmentally friendly enzymatic reaction presented up to 100% of conversion; moreover, the production of possible by-products was minimized controlling reaction time and amount of enzyme. Furthermore, the presence of chloroform was evaluated during the enzymatic reactions and despite high conversions with higher enzyme concentration, the solvent-free system showed fast kinetics even with 1.13 U/g substrates. In addition, the commercial immobilized lipases Novozym 435 and NS 88011 could be applied for up to 10 cycles keeping conversions about 90%. The scale-up of the reaction was possible and a purification procedure was applied in order to isolate the diene ester monomer 2-(10-undecenoyloxy)ethyl methacrylate, preserving its double bonds, which could allow a potential use of this product in the synthesis of new renewable polymers through techniques as metathesis, thiol-ene, or free-radical polymerization.

Hydrophilization of bixin by lipase-catalyzed transesterification with sorbitol

Bixin is one of the most used yellow-orange food colorants in the food industry. The polyene chain of bixin makes it highly hydrophobic and less suitable for water-based food formulations. Lipase-catalyzed reactions of bixin with sorbitol were studied to synthesize a new derivative of bixin with potential hydrophilic properties. Interestingly, we show that the lipase-catalyzed reaction of bixin leads to a transesterification reaction and formation of a transesterified product, sorbitol ester of norbixin (SEN). The reaction efficiency was optimized with various immobilized lipases at different water activity levels in the organic solvent, 2-methyl-2-butanol. Among the examined lipases, immobilized Candida antarctica lipase B (Novozyme 435) provided the highest reaction yield at a water activity close to zero. Tetrahydrofuran (THF) was used as co-solvent to improve bixin solubility. The optimization of the reaction conditions with 20% THF lead to a total reaction yield of 50% of SEN.

Beyond topology: coevolution of structure and flux in metabolic networks

Interactions between the structure of a metabolic network and its functional properties underlie its evolutionary diversification, but the mechanism by which such interactions arise remains elusive. Particularly unclear is whether metabolic fluxes that determine the concentrations of compounds produced by a metabolic network, are causally linked to a network's structure or emerge independently of it. A direct empirical study of populations where both structural and functional properties vary among individuals' metabolic networks is required to establish whether changes in structure affect the distribution of metabolic flux. In a population of house finches (Haemorhous mexicanus), we reconstructed full carotenoid metabolic networks for 442 individuals and uncovered 11 structural variants of this network with different compounds and reactions. We examined the consequences of this structural diversity for the concentrations of plumage-bound carotenoids produced by flux in these networks. We found that concentrations of metabolically derived, but not dietary carotenoids, depended on network structure. Flux was partitioned similarly among compounds in individuals of the same network structure: within each network, compound concentrations were closely correlated. The highest among-individual variation in flux occurred in networks with the strongest among-compound correlations, suggesting that changes in the magnitude, but not the distribution of flux, underlie individual differences in compound concentrations on a static network structure. These findings indicate that the distribution of flux in carotenoid metabolism closely follows network structure. Thus, evolutionary diversification and local adaptations in carotenoid metabolism may depend more on the gain or loss of enzymatic reactions than on changes in flux within a network structure.

Comparison of lipases and glycoside hydrolases as catalysts in synthesis reactions

Lipases and glycoside hydrolases have large similarities concerning reaction mechanisms. Acyl-enzyme intermediates are formed during lipase-catalyzed reactions and in an analogous way, retaining glycoside hydrolases form glycosyl-enzyme intermediates during catalysis. In both cases, the covalent enzyme intermediates can react with water or other nucleophiles containing hydroxyl groups. Simple alcohols are accepted as nucleophiles by both types of enzymes. Lipases are used very successfully in synthesis applications due to their efficiency in catalyzing reversed hydrolysis and transesterification reactions. On the other hand, synthesis applications of glycoside hydrolases are much less developed. Here, important similarities and differences between the enzyme groups are reviewed and approaches to reach high synthesis yields are discussed. Useful strategies include the use of low-water media, high nucleophile concentrations, as well as protein engineering to modify the selectivity of the enzymes. The transglycosylases, hydrolases which naturally catalyze mainly transfer reactions, are of special interest and might be useful guides for engineering of other hydrolases.

Green synthesis of isopropyl myristate in novel single phase medium Part I: Batch optimization studies

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Green synthesis of isopropyl ester in homogenous phase reaction system.

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Candida antarctica Lipase B (CAL-B) enzyme has efficiently catalyzed the esterification of myristic acid and isopropyl alcohol.

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CAL-B activity depends on the polarity of an organic solvent.

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Good operation stability of the enzyme was found in the single phase reaction system.

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High purity of isopropyl myristate was obtained by the cold centrifugation technique.

Isopropyl myristate finds many applications in food, cosmetic and pharmaceutical industries as an emollient, thickening agent, or lubricant. Using a homogeneous reaction phase, non-specific lipase derived from Candida antartica, marketed as Novozym 435, was determined to be most suitable for the enzymatic synthesis of isopropyl myristate. The high molar ratio of alcohol to acid creates novel single phase medium which overcomes mass transfer effects and facilitates downstream processing. The effect of various reaction parameters was optimized to obtain a high yield of isopropyl myristate. Effect of temperature, agitation speed, organic solvent, biocatalyst loading and batch operational stability of the enzyme was systematically studied. The conversion of 87.65% was obtained when the molar ratio of isopropyl alcohol to myristic acid (15:1) was used with 4% (w/w) catalyst loading and agitation speed of 150 rpm at 60 °C. The enzyme has also shown good batch operational stability under optimized conditions.

A microtensiometer capable of measuring water potentials below -10 MPa

Tensiometers sense the chemical potential of water (or water potential, Ψw) in an external phase of interest by measuring the pressure in an internal volume of liquid water in equilibrium with that phase. For sub-saturated phases, the internal pressure is below atmospheric and frequently negative; the liquid is under tension. Here, we present the initial characterization of a new tensiometer based on a microelectromechanical pressure sensor and a nanoporous membrane. We explain the mechanism of operation, fabrication, and calibration of this device. We show that these microtensiometers operate stably out to water potentials below -10 MPa, a tenfold extension of the range of current tensiometers. Finally, we present use of the device to perform an accurate measurement of the equation of state of liquid water at pressures down to -14 MPa. We conclude with a discussion of outstanding design considerations, and of the opportunities opened by the extended range of stability and the small form factor in sensing applications, and in fundamental studies of the thermodynamic properties of water.

Eco-friendly methodology for efficient synthesis and scale-up of 2-ethylhexyl-p-methoxycinnamate using Rhizopus oryzae lipase and its biological evaluation

Lipase-mediated synthesis of phenolic acid esters is a green and economical alternative to current chemical methods. Octyl methoxycinnamate, an important UVB-absorbing compound, was synthesized by the esterification of p-methoxycinnamic acid with 2-ethyl hexanol using Rhizopus oryzae lipase. A molar ratio of 1:2 of p-methoxycinnamic acid and 2-ethyl hexanol was found to give an optimum yield using cyclo-octane (50 ml) as reaction solvent, at a temperature of 45 °C, and 750 U of lipase, resulting in a yield of 91.3 % in 96 h. This reaction was successfully scaled up to 400-ml reaction size where 88.6 %bioconversion was achieved. The synthesized compound was found to have superior antioxidant activity as compared to ascorbic acid. The synthesized compound also exhibited good antimicrobial activity against Escherichia coli, Klebsiella pneumonia, Salmonella typhi, Staphylococcus aures, Candida albicans (yeast), Aspergillus niger, Alternaria solani, and Fussarium oxysporum by well diffusion method in terms of zone of inhibitions (in mm).

A comprehensive study of reaction parameters in the enzymatic production of novel biofuels integrating glycerol into their composition

A comprehensive study of critical parameters in the pig pancreatic lipase (PPL) catalysed transesterification of sunflower oil to novel biofuels integrating glycerol into their composition is reported. The influence of oil/alcohol ratio, temperature, quantity of enzyme and water added and pH have been investigated. The enzymatic activity of PPL was found to be greatly influenced by the pH, reaching notable activities at high pH values (10-12), in contrast to other lipases. The addition of small quantities of NaOH (up to 0.1 mL) as coadjuvant in the transesterification reaction enhances the activity of the enzymes. This remarkable behaviour, reported for the first time, may pave the way for the utilisation of these relatively cheap enzymes in large scale commercial biodiesel production. Besides, a novel biofuels containing glycerol into their composition as mono- and diglycerides using PPL as biocatalyst has been developed.

Microbial lipases: at the interface of aqueous and non-aqueous media. A review

In recent times, biotechnological applications of microbial lipases in synthesis of many organic molecules have rapidly increased in non-aqueous media. Microbial lipases are the 'working horses' in biocatalysis and have been extensively studied when their exceptionally high stability in non-aqueous media has been discovered. Stability of lipases in organic solvents makes them commercially feasibile in the enzymatic esterification reactions. Their stability is affected by temperature, reaction medium, water concentration and by the biocatalyst's preparation. An optimization process for ester synthesis from pilot scale to industrial scale in the reaction medium is discussed. The water released during the esterification process can be controlled over a wide range and has a profound effect on the activity of the lipases. Approaches to lipase catalysis like protein engineering, directed evolution and metagenome approach were studied. This review reports the recent development in the field ofnon-aqueous microbial lipase catalysis and factors controlling the esterification/transesterification processes in organic media.

Lipases in lipophilization reactions

Lipases are used in various sectors, as pharmaceutical, food or detergency industry. Their advantage versus classical chemical catalysts is that they exhibit a better selectivity and operate in milder reaction conditions. Theses enzymes can also be used in lipophilization reactions corresponding to the grafting of a lipophilic moiety to a hydrophilic one such as sugar, amino acids and proteins, or phenolic compounds. The major difficulty to overcome in such enzyme-catalyzed reaction resides in the fact that the two involved substrates greatly differ in term of polarity and solvent affinity. Therefore, several key parameters are to be considered in order to achieve the reaction in satisfactory kinetics and yields. The present review discusses the nature of such parameters (eg solvent nature, water activity, chemical modification of substrates) and illustrates their effect with examples of lipase-catalyzed lipophilization reactions of various sugar, amino acids or phenolic derivatives.

Lipase-catalyzed esterification of conjugated linoleic acid with l-carnitine in solvent-free system and acetonitrile

Lipase-catalyzed esterification of conjugated linoleic acid (CLA) with L-carnitine in solvent-free system and acetonitrile was studied. Three lipases (Novzym 435, Amamo AY30 and Amano AYS) have been assayed as suitable biocatalysts in the reaction. It was found that Amano AY30 was the most effective biocatalyst in both solvent-free system and acetonitrile. The conversion rate varied from 8.05 to 60.9% in terms of reaction conditions such as the amount of lipase, the presence of water, the amount of molecular sieves and reaction time. The conversions of substrate in solvent-free system were higher than that in acetonitrile. When the substrates were 1 mmol CLA and 1 mmol L-carnitine, the maximum conversion (60.9%) was obtained in solvent-free system with 150 mg lipase AY30, 50% water content and 150 mg molecular sieves at the reaction time of 24 h. A novel CLA ester product was successfully isolated and characterized by ESI-MS and (1)H NMR.

A water activity control system for enzymatic reactions in organic media

A water activity control system for enzymatic synthesis in organic media, for litre-scale reactors has been constructed. Water activity, a(w), is a key factor when using enzymes in non-conventional media and the optimum value varies for different enzymes. The control system consists of a water activity sensor in the headspace of a jacketed glass reactor (equipped with narrow steel tubes to introduce air), gas-washing bottles containing blue silica gel (a(w)=0) and water (a(w)=1), a PC to monitor water activity and a programmable logic controller (PLC) to control the water activity. The system was evaluated by adjusting water activity in the medium, with a deviation from the set point of less than +/-0.05. Synthesis of cetyl palmitate, under controlled water activity and catalysed by two different lipase preparations, namely, Novozym 435 (immobilised Candida antarctica lipase B) and immobilised Candida rugosa lipase, were also performed. Novozym 435 catalyses reactions very well at extremely low water activity while C. rugosa lipase shows low activity for a(w)<0.5.

The lipase-catalyzed hydrolysis of lutein diesters in non-aqueous media is favored at extremely low water activities

The enzymatic hydrolysis of a mixture of lutein diesters from Marigold flower (Tagetes erecta) was performed both in organic solvents and supercritical CO(2) (SC-CO(2)) using two commercial lipases: lipase B from Candida antarctica (Novozym 435) and the lipase from Mucor miehei (Lipozyme RM IM). Both lipases showed an unexpected dependence of initial reaction rate with the initial water activity (a(wi)) in hexane, with the highest rates of hydrolysis taking place at the lowest a(wi) of the biocatalyst particles. The same result was observed using isooctane, toluene, or SC-CO(2). It is proposed that an increase in a(wi) generates a hydrophilic microenvironment that prevents efficient partitioning of the highly hydrophobic lutein diesters to the enzyme. The critical role of water in this system has not been reported for other hydrolytic reactions in low water media. Calculations of water available for hydrolysis from isotherm analysis, Karl-Fischer titration, and substrate conversion at a(wi) = 0.13, indicate that the extent of reaction is not limited by the amount of available water. Accordingly, the enzyme that holds the largest amount of water after prehydration at the same a(wi) (0.13) will yield the greatest substrate conversion and concentration of the free lutein product. The highest conversion occurred in SC-CO(2), which opens up new opportunities to develop a combined extraction-reaction process for the environmentally benign synthesis of lutein, an important nutraceutical compound.