Effect of mass-transfer limitations on the selectivity of immobilized α-chymotrypsin biocatalysts prepared for use in organic medium

Is enzyme immobilization a mature discipline? Some critical considerations to capitalize on the benefits of immobilization

Enzyme immobilization has been developing since the 1960s and although many industrial biocatalytic processes use the technology to improve enzyme performance, still today we are far from full exploitation of the field. One clear reason is that many evaluate immobilization based on only a few experiments that are not always well-designed. In contrast to many other reviews on the subject, here we highlight the pitfalls of using incorrectly designed immobilization protocols and explain why in many cases sub-optimal results are obtained. We also describe solutions to overcome these challenges and come to the conclusion that recent developments in material science, bioprocess engineering and protein science continue to open new opportunities for the future. In this way, enzyme immobilization, far from being a mature discipline, remains as a subject of high interest and where intense research is still necessary to take full advantage of the possibilities.

Microbial proteases in peptide synthesis: approaches and applications

Enzymatic synthesis of peptides has attracted a great deal of attention in recent years. The proteases from bacterial, fungal, plant, and animal sources have been successfully applied to the synthesis of several small peptides, mainly dipeptides and tripeptides. Peptide bonds can be synthesized using proteases in either a thermodynamically controlled or a kinetically controlled manner. The development of new methods suitable for the large-scale production of biologically active peptides has been actively pursued over the last decade due to their bioactive nature as well as better understanding of their biological functions and properties. The aim of this study was to review the basic techniques of peptide synthesis and some advancement in biotechnological methods for their production.

Effect of mass transfer limitations on the enzymatic kinetic resolution of epoxides in a two-liquid-phase system

Optically active epoxides can be obtained by kinetic resolution of racemic mixtures using enantioselective epoxide hydrolases. To increase the productivity of the conversion of sparingly aqueous soluble epoxides, we investigated the use of a two-phase aqueous/organic system. A kinetic model which takes into account interphase mass transfer, enzymatic reaction, and enzyme inactivation was developed to describe epoxide conversion in the system by the epoxide hydrolase from Agrobacterium radiobacter. A Lewis cell was used to determine model parameters and results from resolutions carried out in the Lewis cell were compared to model predictions to validate the model. It was found that n-octane is a biocompatible immiscible solvent suitable for use as the organic phase. Good agreement between the model predictions and experimental data was found when the enzyme inactivation rate was fitted. Simulations showed that mass transfer limitations have to be avoided in order to maximize the yield of enantiomerically pure epoxide. Resolution of a 39 g/L solution of racemic styrene oxide in octane was successfully carried out in an emulsion batch reactor to obtain (S)-styrene oxide in high enantiomeric excess (>95% e.e.) with a yield of 30%.