Mass Transport Limitations Reduce the Effective Stereospecificity in Enzyme-Catalyzed Kinetic Resolution

Rotticci, Didier; Norin, Torbjörn; Hult, Karl

doi:10.1021/ol005639m

Cited by 47 publications

(33 citation statements)

References 24 publications

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“…However, it is more likely that the large surface area of the buffer layer in the aqua gels enhances phase transfer of benzaldehyde ( 11a ) and mandelonitrile ( 2a ). As already observed earlier, enhancement of the performance of an enzyme upon immobilization is not always due to an improved action of the enzyme [30] .…”

Section: Encapsulation 31supporting

confidence: 62%

“…On this carrier its stereoselectivity and activity is even better than when immobilized as Novozym 435. However, it is also stated that diffusion effects need to be taken into account, emphasizing that there can always be more than one reason why an enzyme performs better/worse when modifying the carrier and that the improvements seen might actually have nothing to do with the carrier [30] . Indeed, Novozym 435 and free CALB were more recently shown to have identical stereoselectivity [31] .…”

Section: Adsorption/electrostatic Interactions 23mentioning

confidence: 99%

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Immobilization as a Tool for Improving Enzymes

Hanefeld

2008

Modern Biocatalysis

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Section: Encapsulation 31supporting

confidence: 62%

Section: Adsorption/electrostatic Interactions 23mentioning

confidence: 99%

Immobilization as a Tool for Improving Enzymes

Hanefeld

2008

Modern Biocatalysis

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“…[32] It is [a] The titrations were performed for 24 h in hexane/diethyl ether (97:3) at a water activity (a w ) 0. 33 thus likely that mass transfer limitations influenced the relative rates of the conversion of the two enantiomers of 1-phenylethanol.…”

Section: Thermomyces Lanuginosus Lipase Immobilised Onto Porous Polypmentioning

confidence: 99%

Factors Governing the Activity of Lyophilised and Immobilised Lipase Preparations in Organic Solvents

2002

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Active site titration and activity measurements were performed in hexane on lyophilised lipase preparations containing different amounts of phosphate buffer and lipase immobilised on porous polypropylene. Lyophilisation of Thermomyces lanuginosus lipase with large quantities of phosphate salts (200 mM) increased the specific activity fourfold, and the number of rapidly titratable active sites increased to 50 % from the 13 % observed when smaller amounts of phosphate buffer were used (20 mM) during lyophilisation. The phosphate buffer worked as an immobilisation matrix for the lipase, and the increase in specific activity was at least partly due to decreased mass transfer limitations. When lipase was immobilised on porous polypropylene, the specific activity was 770 times higher than that of the best freeze-dried preparation. At optimal enzyme loading, 93 % of the enzyme molecules were titrated at a high rate; this indicates that this adsorption on a hydrophobic surface was a very efficient means of reducing mass transfer limitations and of immobilising the enzyme in its active conformation for use in organic solvents. The variation in specific activity with water activity was found to correlate very well with the variation in titratable active sites when lipases from Burkholderia cepacia and Thermomyces lanuginosus were immobilised on porous polypropylene. The catalytic activity per competent active site was thus constant over the whole range of water activities.

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“…Better access to the enzyme molecules could also be the reason for the increment of enantioselectivity induced by all the sugars tested (Table 5.3 ). In fact, Rottici et al [22] showed that immobilized CALB (e.g. Novozym 435), in which the substrate should be less hindered in reaching the catalytic active site, has both higher activity and enantioselectivity with respect to other enzyme preparations (e.g.…”

Section: Why Do Additives Affect the Activity And Enantioselectivity mentioning

confidence: 99%

Importance of Enzyme Formulation for the Activity and Enantioselectivity of Lipases in Organic Solvents

Secundo

2008

Modern Biocatalysis

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5.1 IntroductionLipases are of remarkable practical interest since they have been used in numerous biocatalytic applications, such as kinetic resolution of alcohols and carboxyl esters (both in water and in non -aqueous media) [1] , regioselective acylations of polyhydroxylated compounds, and the preparation of enantiopure amino acids and amides [2,3] . Moreover, lipases are stable in organic solvents, do not require cofactors, possess broad substrate specifi city, and exhibit, in general, a high enantioselectivity. All these features have contributed to make lipases the class of enzyme with the highest number of biocatalytic applications carried out in neat organic solvents.The use of organic solvents is especially advantageous in transforming substrates that are unstable or poorly soluble in water. Furthermore, in the absence of water, the synthesis of ester and amide bonds by hydrolases (mainly lipases and proteases) can be favored over hydrolysis and many side reactions that are water dependent can be prevented. By varying the organic solvent it is also possible to control the substrate specifi city and the regio -and enantioselectivity of a given enzyme. However, although enzymes in organic media show numerous advantages, their catalytic effi ciency is, in most cases, orders of magnitude lower than in aqueous systems. This behavior can be ascribed to different causes such as high saturating substrate concentrations, diffusional limitations, low stabilization of the transition state of the enzyme -substrate intermediate, restricted protein fl exibility, and aggregation and distortions of the enzyme molecules caused by dehydration, which become irreversible in anhydrous solvents [4] .The present chapter briefl y examines and discusses the effects of some additives, namely lyoprotectants (sugars, crown ethers, and methoxypoly(ethylene glycol)), on the activity and enantioselectivity of several lipases. A possible rationale for the increment usually observed when using lyoprotectants, on the basis of conformational data obtained by means of Fourier -transform infrared (FT -IR) spectroscopy is also suggested.

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Mass Transport Limitations Reduce the Effective Stereospecificity in Enzyme-Catalyzed Kinetic Resolution

Cited by 47 publications

References 24 publications

Immobilization as a Tool for Improving Enzymes

Immobilization as a Tool for Improving Enzymes

Factors Governing the Activity of Lyophilised and Immobilised Lipase Preparations in Organic Solvents

Importance of Enzyme Formulation for the Activity and Enantioselectivity of Lipases in Organic Solvents

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