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• 4 different lipases have been immobilized under 16 different conditions. • CALB, CRL and CALA bio catalysts showed slight effects of the immobilization conditions. • RML biocatalysts properties were deeply modulated by the immobilization conditions. • The variables effects showed some covariance. • There is not a universal optimal protocol of RML optimization. Lipases A and B from Candida antarctica (CALA, CALB), and those from Candida rugosa (CRL) and Rhizomucor miehei (RML) have been immobilized on octyl agarose beads under 16 different conditions. The activities of the biocatalysts versus different substrates were analyzed, as well as their thermal stabilities at pH 7.0. All CALB and CRL preparations showed very similar properties, except the CRL biocatalysts prepared at pH 9. Under these conditions the free enzyme was partially inactivated. Immobilized CALA showed some significant differences in activity depending on the immobilization conditions when using esters of mandelic acid as substrates (the activities of the different preparations differed by more than a 2-fold factor), while when using the other substrates the differences were minimal. However, immobilized RML enzyme greatly alters its activity depending on the immobilization conditions, reaching differences up to 4–5 fold in both activity and stability. It is remarkable that the effect of one immobilization variable depends on the substrates, and that there are strong interactions between the different immobilization variables. Thus, this immobilization method was very robust (producing almost identical functional biocatalysts independently from the immobilization conditions) using CRL or CALB, while the immobilization conditions must be carefully controlled using RML to have reproducible results. [ABSTRACT FROM AUTHOR]

This study aimed to optimize free fatty acid production by enzymatic hydrolysis of cottonseed, olive and palm kernel oils in stirred-tank reactors using a lipase from Geotrichum candidum (GCL-I). The effect of pH, temperature and substrate concentration on the hydrolytic activity of GCL-I using these vegetable oils was investigated. Thermal stability tests and thermodynamic studies were also performed. A complete hydrolysis of cottonseed oil was obtained after 120 min of reaction, while for olive and palm kernel maximum hydrolysis percentage was 96.4% and 60.1%, respectively. GCL-I exhibited the highest activity in the hydrolysis of vegetable oils that are rich in unsaturated-fatty acids (cottonseed and olive oils). Under optimal conditions (46.8% m/m of oil, 6.6 U/g of the reaction mixture at 40 °C), complete cottonseed oil hydrolysis was observed at 60 min of reaction performed in an emulsifier-free system with no buffer. [ABSTRACT FROM AUTHOR]

Abstract: A combined docking and molecular dynamics protocol was applied to investigate quercetin binding modes within the catalytic cavity of Candida antarctica lipase B (CALB) and Pseudomonas cepacia lipase (PCL), aiming to explain the difference of specificity of these enzymes in acetylation reaction. For both lipases, docking of quercetin yielded two families of conformers with either the quercetin A or B-ring pointing towards the catalytic residues. Molecular dynamics (MD) calculations were subsequently performed on several complexes of each family. MD trajectories were analyzed focusing on the orientation of the acyl donor bound to the catalytic serine towards the oxyanion hole residues and the proximity of quercetin hydroxyl groups to the catalytic residues. Results showed that with CALB, the acetate was not correctly positioned within the oxyanion hole whatever the orientation of quercetin, suggesting that no product could be obtained. With PCL, the acetate remained within the oxyanion hole during all MD trajectories. Depending on quercetin orientation, either the 7-OH group or the 3, 5, 3′, 4′-OH groups came alternatively near the catalytic residues, suggesting that all of them could be acylated. The capacity of models to explain the regioselectivity of the reaction was discussed. Key residues and interactions involved in quercetin binding modes were identified and related to the reaction feasibility. [Copyright &y& Elsevier]

To investigate the synthetic patterns of triglyceride (triacylglycerol) by lipases in organic solvent, esterification patterns of triglyceride, diglyceride, and monoglyceride were monitored at various reaction times with 10 lipases. As a model study, tricaprin was synthesized from glycerol and capric acids (C10:0) in isooctane. Lipases that were known to give nonspecific hydrolysis in aqueous solvent, such as lipase from Candida cylindracea, Lipase OF-360 (from C. rugosa), and Lipase MY ( C. rugosa) showed nonspecific synthesis of tricaprin in organic solvent (Group I). There are two groups for esterifying trigly cerides in organic solvent with 1,3-specific lipases: one consists of the lipases from Rhizomucor miehei, Pseudomonas aeruginosa (Lipase PS), and Chromobacterium viscosum (Lipase CV) (Group II), and another (Group III) is represented by Lipase AP ( Aspergillus niger), Lipase FAP-15 ( Rhizopus javanicus), and Lipase D ( R. delemar). Although both groups showed 1,3-specific hydrolysis in aqueous solvent, Group III has stricter 1,3-specificity for the synthesis of tricaprin from dicaprin. [ABSTRACT FROM AUTHOR]

The crucial role of silica gel in lipase-catalyzed esterification reactions using adsorbed high-polar substates was established. It was found that in these kinds of reactions, the presence of silica gel-adsorbed substrates did not alter the kinetic mechanisms of the synthesis of acylglycerides but improved significantly the conversion yields. An explanation for the critical role of silica gel in these kinds of reactions was proposed whereby the silica gel behaves as a “polar substrate reservoir” and plays a protective role for the immobilized enzyme avoiding its blockage. In this way it was shown that the use of silica gel facilitates reactions at high glycerol concentrations without alteration of reaction rates or conversion yields. It also was demonstrated that highly hydrophilic polyols enhanced blockage of the enzyme. The importance of the presence of an organic solvent in the reaction medium was shown to have a critical role in the conversion yields of the reactions tested. Finally, the influence of different supports used for adsorption of the substrates was compared with respect to their efficiency in protecting the enzymatic activity. [ABSTRACT FROM AUTHOR]