Inhibition of Candida rugosa lipase by saponins, flavonoids and alkaloids

Lipase inhibitors have generated a great interest because they could help in the prevention or the therapy of lipase-related diseases. Therefore, the aim of the work was to evaluate by HPLC, and using Candida rugosa lipase as model, the inhibitory effect of several saponins: β-aescin, digitonin, glycyrrhizic acid (GA) and Quillaja saponin (QS); flavonoids: 3-hydroxyflavone, 5-hydroxyflavone, (±)-catechin and kaempferol; and alkaloids: aspidospermine, papaverine, physostigmine, pilocarpine, raubasine, rescinnamine, reserpine and trigonelline.

The inhibition produced by most of these compounds is described here for the first time. Saponins appeared very active, being β-aescin and digitonin the most active compounds (IC₅₀ = 0.8–2.4 × 10⁻⁵ M). The inhibitory activity of flavonoids was lower than that of saponins (except GA), and (±)-catechin and kaempferol were the most active. Alkaloids was the most heterogeneous group assayed, varying from rescinnamine, with an IC₁₆ similar to that of digitonin, to papaverine and others which showed almost no inhibition.

In conclusion, β-aescin, digitonin, kaempferol or (±)-catechin, strong lipase inhibitors with a low toxicity and present herbal drugs used for lipase-related diseases such as acne or ulcer, are promising candidates for the prevention or the treatment of these diseases.     

Influence of the organic solvents on the activity in water and the conformation of Candida rugosa lipase: Description of a lipase-activating pretreatment

The influence on lipase activity in water of a pretreatment on Candida rugosa lipase using water miscible and immiscible solvents was studied. The lipase activity in the hydrolysis of esteric substrates in aqueous media increases when the lipase was previously treated with various nearly anhydrous organic media. This activation, which was irreversible, was higher for longer pretreatment times. It was dependent on the pretreatment medium (water activity and solvent used). A relation between variations in the emission intensity and the activities of treated and untreated lipases was found. Activating pretreatment did not shift the peak of fluorescence emission but gave rise to variations in the secondary protein structure by increasing the helical nature. A similar increment in the hydrolysis rate in water can be obtained with the addition of an appropriate amount of solvent (acetonitrile or n-heptane) to the aqueous reaction medium.     

Covalent immobilization of pure isoenzymes from lipase of Candida rugosa

Covalent immobilization of pure lipases A and B from Candida rugosa on agarose and silica is described. The immobilization increases the half-life of the biocatalysts ( ) with respect to the native pure lipases ( ). The percentage immobilization of lipases A and B is similar in both supports (33–40%). The remaining activity of the biocatalysts immobilized on agarose (70–75%) is greater than that of the enzymatic derivatives immobilized on SiO₂ (40–50%). The surface area and the hydrophobic/hydrophilic properties of the support control the lipase activity of these derivatives. The thermal stability of the immobilized lipase A derivatives is greater than that of lipase B derivatives. The nature of the support influences the thermal deactivation profile of the immobilized derivatives. The immobilization in agarose (hydrophilic support) gives biocatalysts that show a greater initial specific reaction rate than the biocatalysts immobilized in SiO₂ (hydrophobic support) using the hydrolysis of the esters of (R) or (S) 2-chloropropanoic and of (R,S) 2-phenylpropanoic acids as the reaction test. The enzymatic derivatives are active for at least 196 h under hydrolysis conditions. The stereospecificity of the native and the immobilized enzymes is the same.     

Esterification of streptol — a cyclitol derivative — by Candida rugosa lipase: influence of the acyl donor on regioselectivity

The influence of the nature of acyl donors on the regioselectivity of Candida rugosa lipase for the esterification of streptol — a cyclitol derivative — was investigated. Excellent regioselectivity for the formation of 3,7-disubstituted derivatives was observed for vinyl butyrate (100% 3,7-derivative, 68% yield) and vinyl propionate (100% 3,7-derivative, 46% yield) as acyl donors. In contrast, for vinyl methacrylate as acyl donor, a mixture of 71% 3,7-derivative and 29% 1,7-derivative was obtained. Varying the chain length, a certain dependency of regioselectivity on the acyl donor was observed, however, no logical correlation satisfying all cases was found. Mono-substituted streptol derivatives were obtained by employing Novozym 243.     

Immobilization in quartz fiber felt reinforced silica aerogel improves the activity of Candida rugosa lipase in organic solvents

Candida rugosa lipase is a very useful catalyst, but its rapid inactivation by simple alcohols is a drawback. The present study was focussed on the encapsulation of this enzyme in silica aerogels reinforced with quartz fiber felt. The activity of the immobilized lipase in an organic solvent could be significantly improved over that of the free enzyme and of previous immobilization techniques, by evaporating the alcohol formed during a pre-hydrolysis of the silica precursor, before adding the aqueous enzyme solution. The alcohol evaporation technique was previously used by other authors to immobilized enzymes, but applied to xerogels dried by evaporation, while in the present case the wet gels obtained were dried by the CO₂ supercritical method to obtain aerogels. Besides, such silica aerogels were also reinforced by impregnating a commercial ceramic quartz fiber felt of St. Gobain with the silica sol containing the enzyme, before gelation. The ceramic composites heterogeneous biocatalysts obtained could be used for a large number of times without any apparent deterioration.     

Immobilization of Candida rugosa lipase on sporopollenin from Lycopodium clavatum

Sporopollenin is a natural polymer obtained from Lycopodium clavatum, which is highly stable with constant chemical structure and has high resistant capacity to chemical attack. In this study, immobilization of lipase from Candida rugosa (CRL) on sporopollenin by adsorption method is reported for the first time. Besides this, the enzyme adsorption capacity, activity and thermal stability of immobilized enzyme have also been investigated. It has been observed that under the optimum conditions (Spo-E_(0.3)), the specific activity of the immobilized lipase on the sporopollenin by adsorption was 16.3 U/mg protein, which is 0.46 times less than that of the free lipase (35.6 U/mg protein). The pH and temperature of immobilized enzyme were optimized, which were 6.0 and 40 °C respectively. Kinetic parameters V_max and K_m were also determined for the immobilized lipase. It was observed that there is an increase of the K_m value (7.54 mM) and a decrease of the V_max value (145.0 U/mg-protein) comparing with that of the free lipase.     

Activation in the family of Candida rugosa isolipases by polyethylene glycol

We have investigated activation of two isoenzymes (lip1 and lip3) from Candida rugosa in polyethylene glycol (PEG) media. Aqueous solutions of PEG 8000 and 20,000 activate lip3 but not lip1 from C. rugosa. Maximum activation (260%) of lip3 requires 6 h of pre-incubation with PEG 8000 (4%, w/v). PEG seems to shift the equilibrium between the open and the closed forms of lip3 towards the active conformation. Inhibition experiments demonstrate that ligands have easier access to the lip3 active site than to the lip1 active site, both in the presence and the absence of PEG.

The presence of PEG in the crystallization medium is responsible for reported differences in the crystal structures of lip1 and lip3. A comparative analysis of crystallographic models of lip1 and lip3 suggests a role for PEG in activation of lip3 and further stabilization of the activated/open form via dimerization in aqueous media.     

Synthesis and characterization of cyclodextrin-based polymers as a support for immobilization of Candida rugosa lipase

The objective of this study was to prepare cross-linked β-cyclodextrin polymers for immobilization of Candida rugosa lipase. The structures of synthesized macrocyclic compounds were characterized by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and scanning electron microscope (SEM) techniques. Properties of the immobilized systems were assessed and their performance on hydrolytic reaction were evaluated and compared with the free enzyme. The influence of activation agents (glutaraldehyde (GA) and hexamethylene diisocyanate (HMDI)) and thermal and pH stabilities of the biocatalyst was evaluated. After the optimization of immobilization process, the physical and chemical characterization of immobilized lipase was performed. Obtained data showed that the immobilized enzyme seemed better and offered some advantages in comparison with free enzyme. It can be observed that the free lipase loses its initial activity within around 80 min at 60 °C, while the immobilized lipases retain their initial activities of about 56% by HMDI and 82% by GA after 120 min of heat treatment at 60 °C.Results showed that the specific activity of the immobilized lipase with glutaraldehyde was 62.75 U/mg protein, which is 28.13 times higher than that of the immobilized lipase with HMDI.     

Amino acid modified chitosan beads: Improved polymer supports for immobilization of lipase from Candida rugosa

Amino acid modified chitosan beads (CBs) for immobilization of lipases from Candida rugosa were prepared by activation of a chitosan backbone with epichlorohydrin followed by amino acid coupling. The beads were analyzed by elemental analysis and solid state NMR with coupling yields of the amino acids ranging from 15 to 60%. The immobilized lipase on unmodified chitosan beads showed the highest immobilization yield (92.7%), but its activity was relatively low (10.4%). However, in spite of low immobilization yields (15–50%), the immobilized lipases on the amino acid modified chitosan beads showed activities higher than that of the unmodified chitosan beads, especially on Ala or Leu modified chitosan beads (Ala-CB or Leu-CB) with 49% activity for Ala-CB and 51% for Leu-CB. The immobilized lipases on Ala-CB improved thermal stability at 55 °C, compared to free and immobilized lipases on unmodified chitosan beads and the immobilized lipase on Ala-CB retained 93% of the initial activity when stored at 4 °C for 4 weeks. In addition, the activity of the immobilized lipase on Ala-CB retained 77% of its high initial activity after 10 times of reuse. The kinetic data (k_cat/K_m) supports that the immobilized lipase on Ala-CB can give better substrate specificity than the unmodified chitosan beads.     

Immobilization of Candida rugosa lipase on colloidal gas aphrons (CGAs)

A novel technique for immobilization of Candida rugosa lipase onto anionic colloidal gas aphrons (CGAs) is described. CGAs are spherical microbubbles (10-100 microm) composed of an inner gas core surrounded by a surfactant shell. In this initial study, greater than 80% lipase (w/w) was effectively retained on the CGAs. Leakage of protein from the CGAs and the activity of the adsorbed lipase decreased with increasing enzyme loading; this indicates that multilayers of lipase may be adsorbing onto the CGAs. The CGA-immobilised lipase displayed normal Michaelis-Menten dependence on substrate concentration and also exhibited greater activity than the free enzyme.     

Molecular modeling of substrate selectivity of Candida antarctica lipase B and Candida rugosa lipase towards c9, t11- and t10, c12-conjugated linoleic acid

Molecular modeling was used to clarify the mechanism of the selectivity of Candida antarctica lipase B and Candida rugosa lipase towards cis9, trans11 (c9, t11-) and trans10, cis12 (t10, c12-) conjugated linoleic acid. Hydrogen bonds network, substrate conformation, binding affinity and water molecules in the binding site were analyzed. Substrate conformation and binding affinity were not correlated with the experimental results of the substrate selectivity. On the contrary, better enzyme preference towards a substrate was correlated with two stronger hydrogen bonds (His-NH-O_a and His-NH-Ser-O_γ) and less water molecules between the substrate the binding pocket. Possible explanation of these was discussed.     

Cross-linked enzyme aggregates (CLEAs) with controlled particles: Application to Candida rugosa lipase

Aggregation agent type and concentration, lipase and glutaraldehyde concentration, and pH are able to affect the formation of cross-linked lipase. The carrier-free immobilized Candida rugosa lipase with a particle size of 40–50 μm showed higher activity than that of the lipase with other particle sizes. The carrier-free immobilized C. rugosa lipase can keep 86% original lipase activity (0.018 g g⁻¹ min⁻¹). The enantioselectivity of the carrier-free immobilized lipase (23.3) was about 1.8 times as much as that of the native lipase (13.0) in kinetic resolution of ibuprofen racemic mixture.     

海藻糖对脂肪酶的保护机理及酶失活动力学

采用自制的磁性固定化酶(MIE),考察了高温下二糖类对酶的保护作用。结果显示:海藻糖对悬浮于水溶液中的MIE没有保护作用;而在高温干燥后,对酶的保护作用效果依次为:海藻糖>乳糖>蔗糖,支持‘玻璃态学说’;此外,采用两步失活动力学模型能够较好的拟合酶的失活过程,并且得到酶的失活速率常数k和半衰期t1/2,加入海藻糖和乳糖之后,MIE的半衰期分别增长了31和23倍。     

Immobilization of Candida rugosa lipase on polypropylene microfiltration membrane modified by glycopolymer: hydrolysis of olive oil in biphasic bioreactor

Polypropylene hollow fiber microfiltration membranes (PPHFMM) with improved hydrophilicity and biocompatibility surface were prepared by the plasma-induced graft polymerization of -allyl glucoside and were used to immobilize lipase from Candida rugosa by adsorption. A biphasic enzyme membrane bioreactor (EMR) was assembled with the glycopolymer-modified and enzyme-immobilized PPHFMM. Effect of operating variables on the performance of this biphasic EMR was investigated with the hydrolysis of olive oil. It was found that, at the optimal operational condition, an apparent volumetric reaction rate of about 0.074 mmol/l h can be obtained. This result indicated that the lipase-immobilized PPHFMM exhibited the catalytic efficiency similar to that of some hydrophilic membranes in biphasic EMR, which verified the feasibility of the employment of surface-hydrophilized polypropylene membranes in such EMR.     

Candida antarctica lipase B catalysed amidation of pyroglutamic acid derivatives. A reaction survey

Pyroglutamic acid esters, both (S)- and (R)-enantiomers, have been studied as substrates of the Candida antarctica lipase B catalyzed amidation in anhydrous organic solvents. They behaved as very good substrates when primary amines or ammonia were used as nucleophiles, affording the corresponding secondary and primary amides, respectively, but did not react with secondary amines. The reaction was enantioselective for the (R)-enantiomer of chiral amines although little kinetic difference was observed between (S)- and (R)-pyroglutamates as acyl donors. As an example of an infrequent reaction, free (S)-pyroglutamic acid may also act as a substrate of the reaction, but is much less reactive than its esters.     

Effects of interactions with micellar interfaces on the activity and structure of different lipolytic isoenzymes from Candida rugosa

The conformational and functional changes of cholesterol esterase (CE) and isolipase (CRL) from Candida rugosa after exposure to a micellar interface and subsequent extraction to a fresh buffer were studied. These two enzymes were activated by interaction with the micellar interface of a sulphosuccinic acid bis[2-ethylhexyl] ester/n-heptane/water system. For the hydrolysis of p-nitrophenyl butyrate ester in water, the catalytic efficiencies of CE and CRL were both improved because on activation their k_cat values increased from 378 to 465 and from 250 to 680 s⁻¹, respectively, while their K_m values decreased from 5.08 × 10⁻⁵ to 3.23 × 10⁻⁵ and from 2.28 × 10⁻⁴ to 1.14 × 10⁻⁴ M, respectively. After exposure to the micelles, CE showed a marked increase in its -helical content from 28 to 49%, but only limited changes were detected when CRL was exposed. These proteins exhibit similar capacities for increasing their -helical content in a helicogenic medium. In acetonitrile/water mixtures, CRL exhibits a partial decrease in the extent of its secondary structure, while CE exhibits an increase in its -helical content. The fact that this medium of reduced polarity permits one to simulate the effect of the AOT reverse micelles on the conformation of CE (increased helicity) but not their effect on the structure of CRL (decreased helicity) supports the hypothesis that only CE interacts to a significant extent with the apolar side of the micellar interface. After exposure to micelles of octyl-β-glucopyranoside, CE (but not CRL) showed a 10% increase in its -helical content.     

Multipoint covalent immobilization of microbial lipase on chitosan and agarose activated by different methods

In this work Candida antarctica lipase type B (CALB) was immobilized on agarose and chitosan. The influence of activation agents (glycidol, glutaraldehyde and epichlorohydrin) and immobilization time (5, 24 and 72 h) on hydrolytic activity, thermal and alkaline stabilities of the biocatalyst was evaluated. Protein concentration and enzymatic activity in the supernatant were determined during the immobilization process. More active derivatives were attained when the enzymatic extract was first purified through dialysis. The highest activities achieved were: for agarose-glyoxyl (with glycidol), 845 U/g of gel, after 72 h of immobilization; for chitosan-glutaraldehyde and agarose-glutaraldehyde, respectively, 1209 U/g of gel and 2716 U/g of gel, after 5 h of immobilization. Thermal stability was significantly increased, when compared to the soluble enzyme: 20-fold for agarose-glyoxyl (with glycidol)-CALB, 18-fold for chitosan-glutaraldehyde-CALB and 21-fold for agarose-glutaraldehyde. The best derivative, 58-fold more stable than the soluble enzyme, was obtained when CALB was immobilized on chitosan activated in two steps, using glycidol and glutaraldehyde, 72 h immobilization time. The stabilization degree of the derivative increased with the immobilization time, an indication that a multipoint covalent attachment between enzyme and the support had really occurred.     

Substrate specificity of lipase B from Candida antarctica in the synthesis of arylaliphatic glycolipids

Arylaliphatic glycolipids are known for their pharmaceutical and medicinal properties. We found that a great variety of arylaliphatic esters can be synthesized from non-activated substrates like glucose or the natural occurring drug salicin using lipase B from Candida antarctica (CAL-B). However, esters based on aromatic carboxylic acids or unsaturated arylaliphatic acids, like cinnamic acid and its derivatives, which are known to display anticancer activity, could not be obtained. In this work, we performed computer-aided molecular modeling based on data of our work published recently and syntheses of new glycolipids to understand why some substances are accepted by CAL-B while some are not. For this purpose, we investigated the accessibility of the lipase binding site for the arylaliphatic acyl donors as well as the steric interactions between the aglycons of glucosides and the residues of the alcohol binding pocket in order to elucidate potentials and limitations of CAL-B for the synthesis of aromatic glycolipids.     

Physical and chemical immobilization of choline oxidase onto different porous solid supports: Adsorption studies

This work carries out for the first time the comparison between the physical and chemical immobilization of choline oxidase onto aminated silica-based porous supports. The influence on the immobilization efficiency of concentration, pH, temperature and contact time between the support and choline oxidase, was evaluated. The immobilization efficiency was estimated taking into consideration the choline oxidase activity, which was assessed by using cadmium telluride (CdTe) quantum dots (QDs), obtained by hydrothermal synthesis, as photoluminescent probes. Hydrogen peroxide produced by enzyme activity was capable of quenching CdTe QDs photoluminescence. The magnitude of the PL quenching process was directly related with the enzyme activity.By comparing the chemical process with the physical adsorption, it was observed that the latter provided the highest choline oxidase immobilization. The equilibrium data were analyzed using Langmuir and Freundlich isotherms and kinetic data were fitted to the pseudo-first-order and pseudo-second-order models. Thermodynamic parameters, such as Gibbs free energy and entropy were also calculated. These results will certainly contribute to the development of new sensing schemes for choline, taking into account the growing demand for its quantification in biological samples.