Assessment of intraparticle biocatalytic distributions as a tool in rational formulation

Combining a Genetically Engineered Oxidase with Hydrogen-Bonded Organic Frameworks (HOFs) for Highly Efficient Biocomposites

Enzymes incorporated into hydrogen-bonded organic frameworks (HOFs) via bottom-up synthesis are promising biocomposites for applications in catalysis and sensing. Here, we explored synthetic incorporation of d-amino acid oxidase (DAAO) with the metal-free tetraamidine/tetracarboxylate-based BioHOF-1 in water. N-terminal enzyme fusion with the positively charged module Zbasic2 strongly boosted the loading (2.5-fold; ≈500 mg enzyme gmaterial-1 ) and the specific activity (6.5-fold; 23 U mg-1 ). The DAAO@BioHOF-1 composites showed superior activity with respect to every reported carrier for the same enzyme and excellent stability during catalyst recycling. Further, extension to other enzymes, including cytochrome P450 BM3 (used in the production of high-value oxyfunctionalized compounds), points to the versatility of genetic engineering as a strategy for the preparation of biohybrid systems with unprecedented properties.

Effects of porous polystyrene resin parameters on Candida antarctica lipase B adsorption, distribution, and polyester synthesis activity

Polystyrene resins with varied particle sizes (35 to 350-600 microm) and pore diameters (300-1000 A) were employed to study the effects of immobilization resin particle size and pore diameter on Candida antarctica Lipase B (CALB) loading, distribution within resins, fraction of active sites, and catalytic properties for polyester synthesis. CALB adsorbed rapidly (saturation time </= 4 min) for particle sizes </= 120 microm (pore size = 300 A). Infrared microspectroscopy showed that CALB forms protein loading fronts regardless of resin particle size at similar enzyme loadings ( approximately 8%). From the IR images, the fractions of total surface area available to the enzyme are 21, 33, 35, 37, and 88% for particle sizes 350-600, 120, 75, 35 microm (pore size 300 A), and 35 microm (pore size 1000 A), respectively. Titration with methyl p-nitrophenyl n-hexylphosphate (MNPHP) showed that the fraction of active CALB molecules adsorbed onto resins was approximately 60%. The fraction of active CALB molecules was invariable as a function of resin particle and pore size. At approximately 8% (w/w) CALB loading, by increasing the immobilization support pore diameter from 300 to 1000 A, the turnover frequency (TOF) of epsilon-caprolactone (epsilon-CL) to polyester increased from 12.4 to 28.2 s-1. However, the epsilon-CL conversion rate was not influenced by changes in resin particle size. Similar trends were observed for condensation polymerizations between 1,8-octanediol and adipic acid. The results herein are compared to those obtained with a similar series of methyl methacrylate resins, where variations in particle size largely affected CALB distribution within resins and catalyst activity for polyester synthesis.

Biocatalysts: Measurement, modelling and design of heterogeneity

Multiple phenomena are involved in conversions by immobilized biocatalysts. A paradox is identified between analytical desires on one hand and analytical boundary conditions on the other: while the study of interdependent phenomena would call for their simultaneous analysis in an integrated context, the available experimental options may impose a series of separate and dedicated analyses. From this analysis, bottlenecks in particle performance may be identified, if possible supported by a mechanistic model and performance criteria. Subsequently, a strategy for further biocatalyst development may be chosen. Finally, possibilities for future improvement of biocatalysts are discussed for various fields of research. Some examples of recent developments in enzyme and matrix characteristics, reactor operation, and micro-technology are discussed.

Effects of macroporous resin size on Candida antarctica lipase B adsorption, fraction of active molecules, and catalytic activity for polyester synthesis

Methyl methacrylate resins with identical average pore diameter (250 A) and surface area (500 m2/g) but with varied particle size (35 to 560-710 microm) were employed to study how immobilization resin particle size influences Candida antarctica Lipase B (CALB) loading, fraction of active sites, and catalytic properties for polyester synthesis. CALB adsorbed more rapidly on smaller beads. Saturation occurred in less than 30 s and 48 h for beads with diameters 35 and 560-710 microm, respectively. Linearization of adsorption isotherm data by the Scatchard analysis showed for the 35 microm resin that: (i) CALB loading at saturation was well below that required to form a monolayer and fully cover the support surface and (ii) CALB has a high affinity for this resin surface. Infrared microspectroscopy showed that CALB forms protein loading fronts for resins with particle sizes 560-710 and 120 microm. In contrast, CALB appears evenly distributed throughout 35 microm resins. By titration with p-nitrophenyl n-hexyl phosphate (MNPHP), the fraction of active CALB molecules adsorbed onto resins was <50% which was not influenced by particle size. The fraction of active CALB molecules on the 35 microm support increased from 30 to 43% as enzyme loading was increased from 0.9 to 5.7% (w/w) leading to increased activity for epsilon-caprolactone (epsilon-CL) ring-opening polymerization. At about 5% w/w CALB loading, by decreasing the immobilization support diameter from 560-710 to 120, 75, and 35 microm, conversion of epsilon-CL % to polyester increased (20 to 36, 42, and 61%, respectively, at 80 min). Similar trends were observed for condensation polymerizations between 1,8-octanediol and adipic acid.

Field-emission scanning electron microscopy analysis of morphology and enzyme distribution within an industrial biocatalytic particle

Field-emission scanning electron microscopy (FESEM) was used in a technical feasibility study to obtain insight into the internal morphology and the intraparticle enzyme distribution of Assemblase, an industrial biocatalytic particle containing immobilized penicillin-G acylase. The results were compared with previous studies based on light and transmission electron microscopic techniques. The integrated FESEM approach yielded the same quantitative results as the microscopic techniques used previously. Given this technical equivalence, the integrated approach offers several advantages. First, the single preparation method and detection system avoids interpretation discrepancies between corresponding areas that were examined for different properties with different detection techniques in different samples. Second, the specimen size suitable for whole particle study is virtually unlimited, which simplifies sectioning and puts less stringent demands on the embedding technique. Furthermore, the sensitivity toward enzyme presence and distribution increases because the epitopes inside thick sections become available for labeling. Quick and unambiguous analysis of the relation between particle morphology and enzyme distribution is important because this information may be used in the future for the design of enzyme distributions in which the particle morphology can be used as a control parameter.

Novel approach to quantify immobilized-enzyme distributions

The quantitative intraparticle enzyme distribution of Assemblase, an industrially employed polydisperse immobilized penicillin-G acylase, was measured. Because of strong autofluorescence of the carrier, the generally applied technique of confocal scanning microscopy could not be used; light microscopy was our method of choice. To do so, Assemblase particles of various sizes were sectioned, labeled with antibodies specifically against the enzyme, and analyzed light microscopically. Image analysis software was developed and used to determine the intraparticle enzyme distribution, which was found to be heterogeneous, with most enzyme located in the outer regions of the particles. Larger particles showed steeper gradients than smaller ones. A mathematical representation of the intraparticle profiles, based on in-stationary enzyme diffusion into the particles, was validated successfully for a broad range of particle sizes using data for volume-averaged particle size and enzyme loading. The enzyme gradients determined in this work will be used as input for a physical model that quantitatively describes the complex behavior of Assemblase. Such a physical model will lead to identification of the current bottlenecks in Assemblase and can serve as a starting point for the design of improved biocatalysts that also may be based on intelligent use of enzyme gradients.

Immobilised enzymes: carrier-bound or carrier-free?

Recent advances have been made in the development of carrier-free immobilised enzymes and several criteria established for the selection of immobilised enzymes for biotransformations. The pros and cons of carrier-free versus carrier-bound immobilised enzymes and of each type of carrier-free enzyme are discussed.