Validating computer simulations of enantioselective catalysis; reproducing the large steric and entropic contributions in Candida Antarctica lipase B

The prospect for computer‐aided refinement of stereoselective enzymes is further validated by simulating the ester hydrolysis by the wild‐type and mutants of CalB, focusing on the challenge of dealing with strong steric effects and entropic contributions. This was done using the empirical valence bond (EVB) method in a quantitative screening of the enantioselectivity, considering both k_cat and k_cat/K_M of the R and S stereoisomers. Although the simulations require very extensive sampling for convergence they give encouraging results and major validation, indicating that our approach offers a powerful tool for computer‐aided design of enantioselective enzymes. This is particularly true in cases with large changes in steric effects where alternative approaches may have difficulties in capturing the interplay between steric clashes with the reacting substrate and protein flexibility. Proteins 2014; 82:1387–1399. © 2014 Wiley Periodicals, Inc.     

Sol-gel immobilization of serine proteases for application in organic solvents

The serine proteases alpha-chymotrypsin, trypsin, and subtilisin Carlsberg were immobilized in a sol-gel matrix and the effects on the enzyme activity in organic media are evaluated. The percentage of immobilized enzyme is 90% in the case of alpha-chymotrypsin and the resulting specific enzyme activity in the transesterification of N-acetyl-L-phenylalanine ethyl ester with 1-propanol in cyclohexane is 43 times higher than that of a nonimmobilized lyophilized alpha-chymotrypsin. The activities of trypsin and subtilisin Carlsberg are enhanced with 437 and 31 times, respectively. The effect of immobilization on the enzyme activity is highest in hydrophobic solvents.     

Dynamic resolution and stereoinversion of secondary alcohols by chemo-enzymatic processes

To overcome the maximum 50% yield limitation of classical resolution methods, deracemization processes involving a racemization step (dynamic resolution) or a prochiral intermediate (stereoinversion) have been developed. The use of transition metal complexes as racemizing agents, in combination with an enzymatic reaction, has been successfully extended to the deracemization of a number of simple or functionalized sec-alcohols. A two-enzyme process has been also investigated for their sequential or simultaneous deracemization. Other prominent results arise from an (apparently general) oxidoreduction process catalyzed by a single whole-cell microorganism.     

Head group specificity of phospholipase D isoenzymes from poppy seedlings (<Emphasis Type="Italic">Papaver somniferum</Emphasis> L.)

The biocatalytical potential of two new phospholipase D (PLD) isoenzymes from poppy seedlings (Papaver somniferum L.), PLD-A and PLD-B, was examined by comparing their activities in phospholipid transformation. Both enzymes showed the same ratio in rates of hydrolysis [phosphatidylcholine (PC):phosphatidylglycerol (PG):phosphatidylserine:phosphatidylinositol=1:0.5:0.3:0.1] and were inactive towards phosphatidylethanolamine (PE). PLD-A did not catalyze head group exchange whereas PLD-B showed a high transphosphatidylation potential in the conversion of PC into PG and PE. This enzyme also catalyzed the transesterification of octadecylphosphocholine into octadecylphosphoglycerol or octadecylphosphoethanolamine.     

Regioselective Enzymatic Synthesis of Non-Steroidal Anti-Inflammatory Drugs Containing Glucose in Organic Media

Enzymatic transesterification of glucose with the vinyl ester of non-steroidal anti-inflammatory drugs (NSAIDs) was in organic media performed for synthesis of novel NSAIDs-glucose conjugates. Glucose was regioselectively acylated at the 6-hydroxyl group. The indomethacin-glucose conjugate and ketoprofen-glucose conjugate were produced by the catalysis of alkaline protease from Bacillus subtilis in the respective yields of 42% (over 48 h) and 63% (over 40 h). The etodolac-glucose conjugate was obtained in 26% yield (over 144 h) by lipase from Candida antarctica.     

Phospholipase D and its application in biocatalysis

Phospholipase D (PLD) from plants or microorganisms is used as biocatalyst in the transformation of phospholipids and phospholipid analogs in both laboratory and industrial scale. In recent years the elucidation of the primary structure of many PLDs from several sources, as well as the resolution of the first crystal structure of a microbial PLD, have yielded new insights into the structural basis and the catalytic mechanism of this catalyst. This review summarizes some new results of PLD research in the light of application.     

Selective Lipase-Catalyzed Esterification of Alkyl Glycosides

Alkyl derivatives of glucose, galactose and fructose were acylated by lipase-catalyzed transesterification with alkanoic esters. The best results were obtained with immobilized Upases of the Candida antarctica type. Primary alcohol functions were acylated first, followed by secondary ones depending on the structure of the glycoside.

The water activity in the reaction medium had a striking effect on both the rate and the selectivity of the process. The size and orientation of the alkyl substituent and the structure of the acyl acceptor were also found to exert a profound influence on the course of the reaction.     

Working at controlled water activity in a continuous process: the gas/solid system as a solution

Fusarium solani cutinase and Candida cylindracea lipase were used to catalyze a transesterification reaction in a continuous gas/solid bioreactor. In this system, a solid phase composed of a packed enzymatic preparation was continuously percolated with carrier gas which fed substrate and removed reaction products simultaneously. Different conditions of immobilization were used and compared to the results obtained with a nonsupported enzyme. The enzymatic activity was found to be highly dependent of a key parameter: water activity (a(w)). Biocatalyst stability was greatly influenced by water activity and the choice of immobilization technique for the enzymatic material. For free and adsorbed enzymes, water requirements exhibited optima which corresponded to the complete hydration coverage of the protein. These optima presented a good correlation with the isotherm sorption curves obtained for the different preparations. In this work are reported the results concerning the possibility of using a continuous system able to operate at controlled water activity in a heterogeneous medium. Lipolytic enzyme in such a system appears to be a new process for the biotransformation of volatile esters. (c) 1995 John Wiley & Sons, Inc.     

Simple screening method for lipase for transesterification in organic solvent

We investigated lipase-catalyzed hydrolysis in water and dioxane—water with a simple colorimetric method. We screened 24 lipases for the ability to hydrolyze p-nitrophenyl esters as chromogenic substrates. Their hydrolytic activities were varied by adding dioxane. Most of the lipases showed high activity in hydrolysis in water, but some showed activity in 50% dioxane—water several tens times higher than those in water. Moreover, several lipases with hydrolytic abilities in 50% dioxane—water also catalyzed the transesterification of p-nitrophenol using fatty acid vinyl esters. We found it possible that a useful lipase for transesterification can be selected by measuring the hydrolysis activity of p-nitrophenyl ester in 50% dioxane—water.