Kinetics of thermal deactivation of enzymes: a simple three parameters phenomenological model can describe the decay of enzyme activity, irrespectively of the mechanism

Improved Solubility and Stability of a Thermostable Carbonic Anhydrase via Fusion with Marine-Derived Intrinsically Disordered Solubility Enhancers

Carbonic anhydrase (CA), an enzyme catalyzing the reversible hydration reaction of carbon dioxide (CO2), is considered a promising biocatalyst for CO2 reduction. The α-CA of Thermovibrio ammonificans (taCA) has emerged as a compelling candidate due to its high thermostability, a critical factor for industrial applications. However, the low-level expression and poor in vitro solubility have hampered further utilization of taCA. Recently, these limitations have been addressed through the fusion of the NEXT tag, a marine-derived, intrinsically disordered small peptide that enhances protein expression and solubility. In this study, the solubility and stability of NEXT-taCA were further investigated. When the linker length between the NEXT tag and the taCA was shortened, the expression level decreased without compromising solubility-enhancing performance. A comparison between the NEXT tag and the NT11 tag demonstrated the NEXT tag's superiority in improving both the expression and solubility of taCA. While the thermostability of taCA was lower than that of the extensively engineered DvCA10, the NEXT-tagged taCA exhibited a 30% improvement in long-term thermostability compared to the untagged taCA, suggesting that enhanced solubility can contribute to enzyme thermostability. Furthermore, the bioprospecting of two intrinsically disordered peptides (Hcr and Hku tags) as novel solubility-enhancing fusion tags was explored, demonstrating their performance in improving the expression and solubility of taCA. These efforts will advance the practical application of taCA and provide tools and insights for enzyme biochemistry and bioengineering.

Multienzyme Coimmobilization on Triheterofunctional Supports

Immobilized multienzyme systems are gaining momentum in applied biocatalysis; however, the coimmobilization of several enzymes on one carrier is still challenging. In this work, we exploited a heterofunctional support activated with three different chemical functionalities to immobilize a wide variety of different enzymes. This support is based on agarose microbeads activated with aldehyde, amino, and cobalt chelate moieties that allow a fast and irreversible immobilization of enzymes, enhancing the thermostability of most of the heterogeneous biocatalysts (up to 21-fold higher than the soluble one). Furthermore, this trifunctional support serves to efficiently coimmobilize a multienzyme system composed of an alcohol dehydrogenase, a reduced nicotinamide adenine dinucleotide (NADH) oxidase, and a catalase. The confined multienzymatic system demonstrates higher performance than its free counterpart, achieving a total turnover number (TTN) of 1 × 10⁵ during five batch consecutive cycles. We envision this solid material as a platform for coimmobilizing multienzyme systems with enhanced properties to catalyze stepwise biotransformations.

Producing Natural Flavours from Isoamyl Alcohol and Fusel Oil by Using Immobilised Rhizopus oryzae Lipase

Enzymatic synthesis of short-chain esters (flavours) might enable their labelling as natural, increasing their value. Covalently immobilised Rhizopus oryzae lipase (EO-proROL) was used to synthesise isoamyl butyrate and acetate. In cyclohexane, the best performer reaction solvent, 1.8 times higher yield of isoamyl butyrate (ca. 100%) than isoamyl acetate (ca. 55%) was obtained. Optimum initial acid concentration (410 mM) and acid:alcohol mole ratio (0.5) were established by a central composite rotatable design to maximise isoamyl butyrate single-batch and cumulative production with reused enzyme. These conditions were used to scale up the esterification (150 mL) and to assess yield, initial esterification rate, productivity and enzyme operational stability. Commercial isoamyl alcohol and fusel oil results were found to be similar as regards yield (91% vs. 84%), initial reaction rate (5.4 µM min−1 with both substrates), operational stability (40% activity loss after five runs with both) and productivity (31.09 vs. 28.7 mM h−1). EO-proROL specificity for the structural isomers of isoamyl alcohol was also evaluated. Thus, a successful biocatalyst and product conditions ready to be used for isoamyl ester industrial production are here proposed.

Improved stability and promoted activity of laccase by One-Pot encapsulation with Cu (PABA) nanoarchitectonics and its application for removal of Azo dyes

Immobilization of laccase helps protect the laccase and realizes repeated use. However, excessive encapsulation protection will also limit the release of laccase activity. This work introduces an effective one-pot method encapsulating laccase in the porous material of metal organic framework (MOF) containing specific metal ions, which provided a new way to solve the problem of limited laccase activity. The immobilization process was mathematically modeled. The morphological and encapsulated properties of the prepared materials were confirmed by the characterization results of SEM, FTIR, XRD, TGA, XPS and CLSM. The results showed that laccase was successfully encapsulated, and the Cu (PABA) with Cu2+ as the central structure promoted the laccase activity, the activity of immobilized laccase increased by 1.7 times. The prepared laccase@Cu (PABA) (Lac@Cu (PABA)) showed enhanced stability to extreme pH, high temperature and storage time. More importantly, the Lac@Cu (PABA) exhibited superior reusability, maintaining 70% removal rate of Direct Red 31 (DR31) even after 10 cycles. The dye removal rate of immobilized laccase reached 92% in 6 h under optimal conditions. This research improved the stability of laccase while releasing the activity of laccase, which not only broadened the applicable environment of laccase, but also increased the rate of degradation, and provided a new idea for the clean and efficient treatment of water pollution in textile industry.

Experimental and mathematical modeling approaches for biocatalytic post-consumer poly(ethylene terephthalate) hydrolysis

The environmental impact arising from poly(ethylene terephthalate) (PET) waste is notable worldwide. Enzymatic PET hydrolysis can provide chemicals that serve as intermediates for value-added product synthesis and savings in the resources. In the present work, some reaction parameters were evaluated on the hydrolysis of post-consumer PET (PC-PET) using a cutinase from Humicola insolens (HiC). The increase in PC-PET specific area leads to an 8.5-fold increase of the initial enzymatic hydrolysis rate (from 0.2 to 1.7 mmol L^-1 h^-1), showing that this parameter plays a crucial role in PET hydrolysis reaction. The effect of HiC concentration was investigated, and the enzymatic PC-PET hydrolysis kinetic parameters were estimated based on three different mathematical models describing heterogeneous biocatalysis. The model that best fits the experimental data (R² = 0.981) indicated 1.68 mg_protein mL^-1 as a maximum value of the enzyme concentration to optimize the reaction rate. The HiC thermal stability was evaluated, considering that it is a key parameter for its efficient use in PET degradation. The enzyme half-life was shown to be 110 h at 70 ºC and pH 7.0, which outperforms most of the known enzymes displaying PET hydrolysis activity. The results evidence that HiC is a very promising biocatalyst for efficient PET depolymerization.

Constitutive Expression in Komagataella phaffii of Mature Rhizopus oryzae Lipase Jointly with Its Truncated Prosequence Improves Production and the Biocatalyst Operational Stability

Rhizopus oryzae lipase (ROL) containing 28 C-terminal amino acids of the prosequence fused to the N-terminal mature sequence in ROL (proROL) was successfully expressed in the methylotrophic yeast Komagataella phaffii (Pichia pastoris) under the constitutive glyceraldehyde-3-phosphate dehydrogenase promoter (PGAP). Although the sequence encoding the mature lipase (rROL) was also transformed, no clones were obtained after three transformation cycles, which highlights the importance of the truncated prosequence to obtain viable transformed clones. Batch cultures of the K. phaffii strain constitutively expressing proROL scarcely influenced growth rate and exhibited a final activity and volumetric productivity more than six times higher than those obtained with proROL from K. phaffii under the methanol-inducible alcohol oxidase 1 promoter (PAOX1). The previous differences were less marked in fed-batch cultures. N-terminal analysis confirmed the presence of the 28 amino acids in proROL. In addition, immobilized proROL exhibited increased tolerance of organic solvents and an operational stability 0.25 and 3 times higher than that of immobilized rROL in biodiesel and ethyl butyrate production, respectively. Therefore, the truncated prosequence enables constitutive proROL production, boosts bioprocess performance and provides a more stable biocatalyst in two reactions in which lipases are mostly used at industrial level, esterification (ethyl butyrate) and transesterification (biodiesel).

The study of laccase immobilization optimization and stability improvement on CTAB-KOH modified biochar

BACKGROUND

Although laccase has a good catalytic oxidation ability, free laccase shows a poor stability. Enzyme immobilization is a common method to improve enzyme stability and endow the enzyme with reusability. Adsorption is the simplest and common method. Modified biochar has attracted great attention due to its excellent performance.

RESULTS

In this paper, cetyltrimethylammonium bromide (CTAB)-KOH modified biochar (CKMB) was used to immobilize laccase by adsorption method (laccase@CKMB). Based on the results of the single-factor experiments, the optimal loading conditions of laccase@CKMB were studied with the assistance of Design-Expert 12 and response surface methods. The predicted optimal experimental conditions were laccase dosage 1.78 mg/mL, pH 3.1 and 312 K. Under these conditions, the activity recovery of laccase@CKMB was the highest, reaching 61.78%. Then, the CKMB and laccase@CKMB were characterized by TGA, FT-IR, XRD, BET and SEM, and the results showed that laccase could be well immobilized on CKMB, the maximum enzyme loading could reach 57.5 mg/g. Compared to free laccase, the storage and pH stability of laccase@CKMB was improved greatly. The laccase@CKMB retained about 40% of relative activity (4 °C, 30 days) and more than 50% of relative activity at pH 2.0-6.0. In addition, the laccase@CKMB indicated the reusability up to 6 reaction cycles while retaining 45.1% of relative activity. Moreover, the thermal deactivation kinetic studies of laccase@CKMB showed a lower k value (0.00275 min^- 1) and higher t_1/2 values (252.0 min) than the k value (0.00573 min^- 1) and t_1/2 values (121.0 min) of free laccase.

CONCLUSIONS

We explored scientific and reasonable immobilization conditions of laccase@CKMB, and the laccase@CKMB possessed relatively better stabilities, which gave the immobilization of laccase on this cheap and easily available carrier material the possibility of industrial applications.

Functionalization of Porous Cellulose with Glyoxyl Groups as a Carrier for Enzyme Immobilization and Stabilization

The functionalization of the internal surface of macroporous carriers with glyoxyl groups has proven to highly stabilize a large variety of enzymes through multipoint covalent immobilization. In this work, we have translated the surface chemistry developed for the fabrication of glyoxyl-agarose carriers to macroporous cellulose (CEL). To that aim, CEL-based microbeads were functionalized with glyoxyl groups through a stepwise alkoxylation (or alkylation)/oxidation synthetic scheme. This functionalization sequence was analyzed by solid-state NMR, while the scanning electron miscroscopy of CEL microbeads reveals that the mild oxidation conditions negligibly affect the morphological properties of the material. Through the optimal functionalization protocol using rac-glycidol, we introduce up to 200 μmols of aldehyde groups per gram of wet CEL, a similar density to the one obtained for the benchmarked agarose-glyoxyl carrier. This novel CEL-based carrier succeeds to immobilize and stabilize industrially relevant enzymes such as d-amino acid oxidase from Trigonopsis variabilis and xylanases from Trichoderma reseei. Remarkably, the xylanases immobilized on the optimal CEL-based materials present a half-life time of 51 h at 60 °C and convert up to 90% of the xylan after four operation cycles for the synthesis of xylooligosaccharides.

Chitosan-based CLEAs from Aspergillus niger type A feruloyl esterase: high-productivity biocatalyst for alkyl ferulate synthesis

The enzymatic synthesis of alkyl ferulates is an important reaction in cosmetic and pharmaceutical chemistries, since it may allow to expand the biorefinery concept valorizing biomass wastes enriched in ferulic acid. However, robust biocatalysts for that purpose are scarce. Herein, we have immobilized the type A feruloyl esterase from Aspergillus niger (AnFaeA) as cross-linked enzyme aggregates, employing chitosan as co-feeder (ChCLEAs). High immobilization yields and relative activity recovery were attained in all assessed conditions (> 93%). Furthermore, we enhanced the thermal stability of the soluble enzyme 32-fold. AnFaeA-ChCLEAs were capable to quantitatively perform the solvent-free direct esterification of short- to medium-chain alkyl ferulates (C4-C12) in less than 24 h. By raising the operational temperature to 50 °C, AnFaeA-ChCLEAs transformed 350 mM ferulic acid into isopentyl ferulate with a space-time yield of 46.1 g of product × L^-1 × day^-1, 73-fold higher than previously reported. The overall sustainability of this alkyl ferulate production bioprocess is supported by the high total turnover number (TTN 7 × 10⁵) and the calculated green metrics (E factor = 30). Therefore, we herein present a robust, efficient, and versatile heterogeneous biocatalyst useful for the synthesis of a wide diversity of alkyl ferulates. KEY POINTS: • CLEAs of feruloyl esterase A from A. niger using chitosan as co-feeder were obtained. • Microenvironment of the biocatalysts allowed to obtain C1 to C18 alkyl ferulates. • Biocatalyst at boundary conditions showed a high productivity of 46 g/L day. Graphical Abstract.

Stabilization of ω-transaminase from Pseudomonas fluorescens by immobilization techniques

Transaminases are a class of enzymes with promising applications for the preparation and resolution of a vast diversity of valued amines. Their poor operational stability has fueled many investigations on its stabilization due to their biotechnological relevance. In this work, we screened the stabilization of the tetrameric ω-transaminase from Pseudomonas fluorescens (PfωTA) through both carrier-bound and carrier-free immobilization techniques. The best heterogeneous biocatalyst was the PfωTA immobilized as cross-linked enzyme aggregates (PfωTA-CLEA) which resulted after studying different parameters as the precipitant, additives and glutaraldehyde concentrations. The best conditions for maximum recovered activity (29 %) and maximum thermostability at 60 ºC and 70 ºC (100 % and 71 % residual activity after 1 h, respectively) were achieved by enzyme precipitation with 90% acetone or ethanol, in presence of BSA (100 mg/mL) and employing glutaraldehyde (100 mM) as cross-linker. Studies on different conditions for PfωTA-CLEA preparation yielded a biocatalyst that exhibited 31 and 4.6 times enhanced thermal stability at 60 °C and 70 °C, respectively, compared to its soluble counterpart. The PfωTA-CLEA was successfully used in the bioamination of 4-hydroxybenzaldehyde to 4-hydroxybenzylamine. To the best of our knowledge, this is the first report describing a transaminase cross-linked enzyme aggregates as immobilization strategy to generate a biocatalyst with outstanding thermostability.

Carrier-bound and carrier-free immobilization of type A feruloyl esterase from Aspergillus niger: Searching for an operationally stable heterogeneous biocatalyst for the synthesis of butyl hydroxycinnamates

Feruloyl esterases synthesize butyl hydroxycinnamates, molecules possessing interesting biological properties, nonetheless, they exhibit a low stability under synthesis conditions in organic solvents, restricting its use. To enhance its operational stability in synthesis, we immobilized type A feruloyl esterase from Aspergillus niger (AnFAEA) using several carrier-bound and carrier-free strategies. The most active biocatalysts were: 1) AnFAEA immobilized on epoxy-activated carriers (protein load of 0.6 mg_enzyme x mg^-1_carrier) that recovered 91 % of the initial hydrolytic activity, and 2) AnFAEA aggregated and cross-linked in the presence of 5 mg of BSA and 15 mM of glutaraldehyde (AnFAEA-amino-CLEAs), which exhibited 385 % of its initial hydrolytic activity; both using 4-nitrophenyl butyrate as substrate. The AnFAEA-amino-CLEAs were 12.7 times more thermostable at 60 °C than the AnFAEA immobilized on epoxy-activated carrier, thus AnFAEA-amino-CLEAs were selected for further characterization. Interestingly, during methyl sinapate hydrolysis (pH 7.2 and 30 °C), AnFAEA-amino-CLEAs K_M was 15 % higher, while during butyl sinapate synthesis the K_M was reduced in 63 %, both compared with the soluble enzyme. The direct esterification of butyl sinapate at solvent free conditions using sinapic acid 50 mM, reached 95 % conversion after 24 h employing AnFAEA-amino-CLEAs, which could be used for 10 cycles without significant activity losses, demonstrating their outstanding operational stability.

Investigation of a Weak Temperature-Rate Relationship in the Carbamoylation of a Barbituric Acid Pharmaceutical Intermediate

The rate of reaction between N, N'-dicyclohexylbarbituric acid 1 and ethyl 2-isocyanatoacetate 2 is invariant with temperature. Positive orders in each reactant and dissociation of triethylammonium salts of 1 and product 3 at elevated temperature indicate that reaction occurs via a catalytic mechanism where changes to the positions of equilibria negate changes in the rate of the turnover-limiting step. A model for the consumption of 1 in a flow reactor accurately predicted the outcome of a laboratory-scale multivariate study.

Catalytic power of enzymes decreases with temperature: New insights for understanding soil C cycling and microbial ecology under warming

Most current models of soil C dynamics predict that climate warming will accelerate soil C mineralization, resulting in a long-term CO₂ release and positive feedback to global warming. However, ecosystem warming experiments show that CO₂ loss from warmed soils declines to control levels within a few years. Here, we explore the temperature dependence of enzymatic conversion of polymerized soil organic C (SOC) into assimilable compounds, which is presumed the rate-limiting step of SOC mineralization. Combining literature review, modelling and enzyme assays, we studied the effect of temperature on activity of enzymes considering their thermal inactivation and catalytic activity. We defined the catalytic power of enzymes (E_power ) as the cumulative amount of degraded substrate by one unit of enzyme until its complete inactivation. We show a universal pattern of enzyme's thermodynamic properties: activation energy of catalytic activity (EA_cat ) < activation energy of thermal inactivation (EA_inact ). By investing in stable enzymes (high EA_inact ) having high catalytic activity (low EA_cat ), microorganisms may maximize the E_power of their enzymes. The counterpart of such EAs' hierarchical pattern is the higher relative temperature sensitivity of enzyme inactivation than catalysis, resulting in a reduction in E_power under warming. Our findings could explain the decrease with temperature in soil enzyme pools, microbial biomass (MB) and carbon use efficiency (CUE) reported in some warming experiments and studies monitoring the seasonal variation in soil enzymes. They also suggest that a decrease in soil enzyme pools due to their faster inactivation under warming contributes to the observed attenuation of warming effect on soil C mineralization. This testable theory predicts that the ultimate response of SOC degradation to warming can be positive or negative depending on the relative temperature response of E_power and microbial production of enzymes.

Different strategies for multi-enzyme cascade reaction for chiral vic-1,2-diol production

The stereoselective three-enzyme cascade for the one-pot synthesis of (1S,2S)-1-phenylpropane-1,2-diol ((1S,2S)-1-PPD) from inexpensive starting substrates, benzaldehyde and acetaldehyde, was explored. By coupling stereoselective carboligation catalyzed by benzoylformate decarboxylase (BFD), L-selective reduction of a carbonyl group with alcohol dehydrogenase from Lactobacillus brevis (ADHLb) as well as the coenzyme regeneration by formate dehydrogenase (FDH), enantiomerically pure diastereoselective 1,2-diol was produced. Two different multi-enzyme system approaches were applied: the sequential two-step one-pot and the simultaneous one-pot cascade. All enzymes were kinetically characterized. The impact of acetaldehyde on the BFD and ADHLb stability was investigated. To overcome the kinetic limitation of acetaldehyde in the carboligation reaction and to reduce its influence on the enzyme stability, experiments were performed in two different excesses of acetaldehyde (100 and 300%). Due to the ADHLb deactivation by acetaldehyde, the simultaneous one-pot cascade proved not to be the first choice for the investigated three-enzyme system. In the sequential cascade with 300% acetaldehyde excess a 100% yield of vic 1,2-diol was reached.

Two-Step Production of Phenylpyruvic Acid from L-Phenylalanine by Growing and Resting Cells of Engineered Escherichia coli: Process Optimization and Kinetics Modeling

Phenylpyruvic acid (PPA) is widely used in the pharmaceutical, food, and chemical industries. Here, a two-step bioconversion process, involving growing and resting cells, was established to produce PPA from l-phenylalanine using the engineered Escherichia coli constructed previously. First, the biotransformation conditions for growing cells were optimized (l-phenylalanine concentration 20.0 g·L-1, temperature 35°C) and a two-stage temperature control strategy (keep 20°C for 12 h and increase the temperature to 35°C until the end of biotransformation) was performed. The biotransformation conditions for resting cells were then optimized in 3-L bioreactor and the optimized conditions were as follows: agitation speed 500 rpm, aeration rate 1.5 vvm, and l-phenylalanine concentration 30 g·L-1. The total maximal production (mass conversion rate) reached 29.8 ± 2.1 g·L-1 (99.3%) and 75.1 ± 2.5 g·L-1 (93.9%) in the flask and 3-L bioreactor, respectively. Finally, a kinetic model was established, and it was revealed that the substrate and product inhibition were the main limiting factors for resting cell biotransformation.

Kinetics of curcumin oxidation by 2,2-diphenyl-1-picrylhydrazyl (DPPH˙): an interesting case of separated coupled proton-electron transfer

The decay of dpph˙ in absolute ethanol at 25 °C and in the presence of curcumin (1), 4-methylcurcumin (3), 4,4-dimethylcurcumin (4) or curcumin 4'-methyl ether (5) follows bi-exponential kinetics. These unusual reaction kinetics are compatible with a two-step process in which an intermediate accumulates in a reversible first step followed by an irreversible process. As in other similar cases (Foti et al., Org. Lett., 2011, 13, 4826-4829), we have hypothesised that the intermediate is a π-stacked complex, formed between one curcumin anion (in the case of 1, 3 and 5 the enolate anion) and the picryl moiety of dpph˙, in which an intra-complex electron transfer from the (enolate) anion takes place. By comparing the kinetics of curcumin 4',4''-dimethyl ether (2) (no phenolic OH), (5) (one phenolic OH) and (1) (two phenolic OHs), we have deduced that the electron transfer process must be accompanied by a simultaneous proton transfer from the phenolic OHs to the bulk solvent (separated coupled proton-electron transfer). The rate constants kα for the forward reaction of 2, 5 and 1 with dpph˙ are in fact ∼0, 7.5 × 10(3) and 1.8 × 10(4) M(-1) s(-1), respectively, in a clear dependence on the number of phenolic OHs.

Analysis of heterogeneity in nonspecific PEGylation reactions of biomolecules

The compositional heterogeneity associated with polymer conjugation reactions of biomolecules is analyzed for the particular case of nonspecific PEGylation reactions. It is shown that the distribution of the number of PEG moieties grafted to biomolecules such as proteins is a binomial-type function of two parameters-the reaction efficiency as well as the number of binding sites per biomolecule. The nature of this distribution implies that uniform compositions are favored for increasing number of coupling sites per biomolecule as well as for increasing efficiency of the modification process. Therefore, the binomial distribution provides a rationale for the pronounced heterogeneity that is observed for PEGylated small enzyme systems even at high coupling efficiencies. For the particular case of PEGylated trypsin it is shown that the heterogeneity results in a broad distribution of deactivation times that is captured by a stretched exponential decay model. The presented analysis is expected to apply to general modification processes of compounds in which partial functionalization of a fixed number of reactive sites is achieved by means of a nonspecific coupling reaction.

Bacterial versus fungal laccase: potential for micropollutant degradation

Relatively high concentrations of micropollutants in municipal wastewater treatment plant (WWTP) effluents underscore the necessity to develop additional treatment steps prior to discharge of treated wastewater. Microorganisms that produce unspecific oxidative enzymes such as laccases are a potential means to improve biodegradation of these compounds. Four strains of the bacterial genus Streptomyces (S. cyaneus, S. ipomoea, S. griseus and S. psammoticus) and the white-rot fungus Trametes versicolor were studied for their ability to produce active extracellular laccase in biologically treated wastewater with different carbon sources. Among the Streptomyces strains evaluated, only S. cyaneus produced extracellular laccase with sufficient activity to envisage its potential use in WWTPs. Laccase activity produced by T. versicolor was more than 20 times greater, the highest activity being observed with ash branches as the sole carbon source. The laccase preparation of S. cyaneus (abbreviated L_Sc) and commercial laccase from T. versicolor (L_Tv) were further compared in terms of their activity at different pH and temperatures, their stability, their substrate range, and their micropollutant oxidation efficiency. L_Sc and L_Tv showed highest activities under acidic conditions (around pH 3 to 5), but L_Tv was active over wider pH and temperature ranges than L_Sc, especially at near-neutral pH and between 10 and 25°C (typical conditions found in WWTPs). L_Tv was also less affected by pH inactivation. Both laccase preparations oxidized the three micropollutants tested, bisphenol A, diclofenac and mefenamic acid, with faster degradation kinetics observed for L_Tv. Overall, T. versicolor appeared to be the better candidate to remove micropollutants from wastewater in a dedicated post-treatment step.

Enhanced bioethanol production from pretreated corn stover via multi-positive effect of casein micelles

Casein polypeptides containing substructures of αs1-casein, β-casein, k-casein, αs2-casein were used as a lignin-blocker at above critical micelles concentration to improve the bioethanol production of dilute acid, lime, alkali, extrusion and AFEX pretreated corn stover (CS). Application of 0.5 g/g glucan of casein was found to effectively increase the glucose yield of CS pretreated with dilute acid, lime, alkali, extrusion and AFEX by 31.9%, 17.0%, 22.7%, 29.5%, and 17.4%, respectively with no positive impact on Avicel. Consequently 96 h simultaneous saccharification and fermentation (SSF) of these hydrolysates reduced the fermentation period by up to 48 h and increased the theoretical yield of ethanol by 8.48-33.7% compared to control. Application of casein during saccharification reduced the enzyme utilization by 33.0%. Recycling of hydrolysate from casein-treated CS for a 2nd round hydrolysis resulted in average glucose yield of 36.4% compared to 29.0% control.

Rational approach to optimize cellulase mixtures for hydrolysis of regenerated cellulose containing residual ionic liquid

For the efficient production of glucose for platform chemicals or biofuels, cellulosic biomass is pretreated and subsequently hydrolyzed with cellulases. Although ionic liquids (IL) are known to effectively pretreat cellulosic biomass, the hydrolysis of IL pretreated biomass has not been optimized so far. Here, we present a semi-empirical model to rationally optimize the hydrolysis of pretreated α-cellulose - regenerated from IL and containing residual IL from the pretreatment. First, the influence of the IL MMIM DMP on the individual cellulases endoglucanase I, cellobiohydrolase I and β-glucosidase was investigated. Second, an enzyme loading-dependent model was developed to describe kinetics for the individual cellulases and cellulase mixtures. Third, this model was used to optimize the cellulase mixture for the efficient hydrolysis of regenerated cellulose containing residual IL. Finally, we could significantly increase the initial hydrolysis rate in 10% (v/v) MMIM DMP by 49% and the sugar yield by 10% points.

Cross-linked enzyme aggregates of β-glucosidase from Prunus domestica seeds

Cross-linked enzyme aggregates (CLEAs) of β-glucosidase were prepared and characterized. Under the optimum conditions, the activity recovery of CLEAs reached 84 %. The reduction by NaBH(4) resulted in slightly lower activities of CLEAs, while their thermostability was enhanced. CLEAs were more thermally stable than free enzyme (half lives, 973 vs. 518 min at 50 °C), while less stable than seed meal (half life, 1,090 min). In 90 % (v/v) t-butanol, the half lives of CLEAs and free enzyme were 53 and 6.7 h, respectively. Besides, the catalytic efficiency (V (max)/K (m)) of CLEAs was comparable to free enzyme (0.42 vs. 0.47 min(-1) mg(-1)). This carrier-free immobilized enzyme had a network structure with multiple layers. The productivity of salidroside using CLEAs reached 150 g/l g catalyst, while being 6.3 g/l g with seed meal.

Continuous steroid biotransformations in microchannel reactors

The use of microchannel reactor based technologies within the scope of bioprocesses as process intensification and production platforms is gaining momentum. Such trend can be ascribed a particular set of characteristics of microchannel reactors, namely the enhanced mass and heat transfer, combined with easier handling and smaller volumes required, as compared to traditional reactors. In the present work, a continuous production process of 4-cholesten-3-one by the enzymatic oxidation of cholesterol without the formation of any by-product was assessed. The production was carried out within Y-shaped microchannel reactors in an aqueous-organic two-phase system. Substrate was delivered from the organic phase to aqueous phase containing cholesterol oxidase and the product formed partitions back to the organic phase. The aqueous phase was then forced through a plug-flow reactor, containing immobilized catalase. This step aimed at the reduction of hydrogen peroxide formed as a by-product during cholesterol oxidation, to avoid cholesterol oxidase deactivation due to said by-product. This setup was compared with traditional reactors and modes of operation. The results showed that microchannel reactor geometry outperformed traditional stirred tank and plug-flow reactors reaching similar conversion yields at reduced residence time. Coupling the plug-flow reactor containing catalase enabled aqueous phase reuse with maintenance of 30% catalytic activity of cholesterol oxidase while eliminating hydrogen peroxide. A final production of 36 m of cholestenone was reached after 300 hours of operation.

Studies of laccase from Trametes versicolor in aqueous solutions of several methylimidazolium ionic liquids

Stability and kinetic behavior of laccase from Trametes versicolor in the presence of several ionic liquids from the methylimidazolium family have been investigated. In general laccase stability diminished as the size of the alkylic substitute in the methylimidazolium ring increased. Higher concentrations of ionic liquids caused more destabilization than lower ones. Thus, low concentrations of [C(2)mim(+)][EtSO(4)(-)] allowed maintaining enzymatic stability. [C(4)mim(+)][Cl(-)] appeared to have a stabilizing effect on laccase, as little activity decay was observed within three weeks. Kinetic studies indicated that both [C(2)mim(+)][EtSO(4)(-)] and [C(4)mim(+)][Cl(-)] inhibited laccase activity, although 10-fold more [C(2)mim(+)][EtSO(4)(-)] than [C(4)mim(+)][Cl(-)] was required to cause the same degree of inhibition. A kinetic model was developed to represent the experimental data.

Laccase-Based CLEAs: Chitosan as a Novel Cross-Linking Agent

Laccase from Coriolopsis Polyzona was insolubilized as cross-linked enzyme aggregates (CLEAs) for the first time with chitosan as the cross-linking agent. Concentrations between 0.01 and 1.867 g/L of chitosan were used and between 0.05 and 600 mM of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The laccase was precipitated using ammonium sulphate and cross-linked simultaneously. Specific activity and thermal stability of these biocatalysts were measured. Activities of up to 737 U/g were obtained when 2,2-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) was used as a substrate. Moreover, the stability of these biocatalysts was improved with regards to thermal degradation compared to free laccase when exposed to denaturing conditions of high temperature and low pH. The CLEAs stability against chemical denaturants was also tested but no significant improvement was detected. The total amount of ABTS to be oxidized during thermal degradation by CLEAs and free laccase was calculated and the insolubilized enzymes were reported to oxidize more substrate than free laccase. The formation conditions were analyzed by response surface methodology in order to determine an optimal environment for the production of efficient laccase-based CLEAs using chitosan as the cross-linking agent. After 24 hours of formation at pH 3 and at 4°C without agitation, the CLEAs exhibit the best specific activity.