The current demands of the world’s biotechnological industries are enhancement in enzyme productivity and development of novel techniques for increasing their shelf life. These requirements are inevitable to facilitate large-scale and economic formulation. Enzyme immobilization provides an excellent base for increasing availability of enzyme to the substrate with greater turnover over a considerable period of time. Several natural and synthetic supports have been assessed for their efficiency for enzyme immobilization. Nowadays, immobilized enzymes are preferred over their free counterpart due to their prolonged availability that curtails redundant downstream and purification processes. Future investigations should endeavor at adopting logistic and sensible entrapment techniques along with innovatively modified supports to improve the state of enzyme immobilization and provide new perspectives to the industrial sector.

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Enzyme immobilization: an overview on techniques and support materials.

The review compiles artificial cascades involving enzymes with a focus on the last 10 years. A cascade is defined as the combination of at least two reaction steps in a single reaction vessel without isolation of the intermediates, whereby at least one step is catalyzed by an enzyme. Additionally, cascades performed in vivo and in vitro are discussed separately, whereby in vivo cascades are defined here as cascades relying on cofactor recycling by the metabolism or on a metabolite from the living organism. The review introduces a systematic classification of the cascades according to the number of enzymes in the linear sequence and differentiates between cascades involving exclusively enzymes and combinations of enzymes with non-natural catalysts or chemical steps. Since the number of examples involving two enzymes is predominant, the two enzyme cascades are further subdivided according to the number, order, and type of redox steps. Furthermore, this classification differentiates between cascades where al...

Artificial Biocatalytic Linear Cascades for Preparation of Organic Molecules

Multi-enzymatic cascade reactions, i.e., the combination of several enzymatic transformations in concurrent one-pot processes, offer considerable advantages: the demand of time, costs and chemicals for product recovery may be reduced, reversible reactions can be driven to completion and the concentration of harmful or unstable compounds can be kept to a minimum. This review summarizes the developments in multi-enzymatic cascades employed for the asymmetric synthesis of chiral alcohols, amines and amino acids, as well as for CC bond formation. In addition, a general classification of biocatalytic cascade systems is provided and bioprocess engineering aspects associated with the topic are discussed.

Multi-Enzymatic Cascade Reactions: Overview and Perspectives

https://pubs.rsc.org/en/content/articlepdf/2017/gc/c6gc02328b

Transaminase biocatalysis: optimization and application

Enzymatic cascade reactions experience tremendous attention by cutting short conventional step-by-step synthesis in a highly efficient and elegant fashion. Focusing on ω-transaminases, this review provides an overview of different biocatalytic strategies to afford a variety of (chiral) amines employing diverse cascade systems: Cascades to shift the reaction equilibrium as well as cascades for the amination of alcohols and nonactivated C–H bonds are discussed. Cascades enable the deracemization of rac-amines, other ones involve biocatalyzed C–C bond formation and C–C bond hydrolysis. Finally, the potential of spontaneous ring closure reactions initiated by ω-transaminases is illustrated.

Recent Developments of Cascade Reactions Involving ω‑Transaminases

Commercially available ω-transaminases ω-TA-117, -113, and Vibrio fluvialis (Vf-AT) have been immobilized in a sol–gel matrix. Improved results were obtained by employing Celite 545 as additive. The immobilized ω-transaminases ω-TA-117, -113, and V. fluvialis (Vf-AT) were tested in the kinetic resolution of α-chiral primary amines. In contrast to the free enzyme ω-TA-117, the sol–gel/celite immobilized enzyme showed activity even at pH 11. Recycling of the sol–gel/Celite 545 immobilized ω-transaminase ω-TA-117 was performed over five reaction cycles without any substantial loss in enantioselectivity and conversion. Finally, the immobilized ω-TA 117 was employed in a one-pot two-step deracemization of rac-mexiletine and rac-4-phenyl-2-butylamine, two pharmacologically relevant amines. The corresponding optically pure (S)-amines were obtained in up to 95% isolated yield (>99% ee).

Nicole Jasmin Müller

Papers

Immobilization of ω-transaminases by encapsulation in a sol–gel/celite matrix

Asymmetric bioreduction of activated alkenes