Warming weather changes the chemical composition of oat hulls.

The current threats of climate change are driving attention away from the petrochemical industry towards more sustainable and bio-based production processes for fuels and speciality chemicals. These processes require suitable low-cost starting material. One potential material assessed here is the oat hull. Its overall chemical composition has so far not been fully characterized. Furthermore, it is not known how it is affected by extreme weather events. Oat hulls (Kerstin and Galant varieties) grown during 'normal' weather years (2016 and 2017) are compared to the harvest of the warmer and drier year (2018). Standard methods for determination of plant chemical composition, with focus on carbohydrate composition, are utilized. Oat hulls grown in 'normal' weather conditions (2017) are rich in lignocellulose (84%), consisting of 35% hemicellulose, 25% lignin and 23% cellulose. Arabinoxylan was found to be the major biopolymer (32%). However, this composition is greatly influenced by weather variations during the oat growth phase. A lignocellulose reduction of 25% was recorded in the warmer and drier 2018 harvest. Additionally, a 6.6-fold increase in starch content, a four-fold increase in protein content and a 60% decrease in phenolic content was noted. Due to its high lignocellulose composition, with an exceptionally large hemicellulose fraction, the chemical composition of oat hulls is unique among agricultural by-products. However, this characteristic is significantly reduced when grown in warmer and drier weather, which could compromise its suitability for use in a successful biorefinery.

Enhanced transglucosylation/hydrolysis ratio of mutants of Pyrococcus furiosus beta-glucosidase: effects of donor concentration, water content, and temperature on activity and selectivity in hexanol.

The transglucosylation reaction catalyzed by wild-type beta-glucosidase CelB from hyperthermophilic Pyrococcus furiosus and active site mutants (M424K, F426Y, M424K/F426Y) was studied. The conversion of pentyl-beta-glucoside to hexyl-beta-glucoside in hexanol was used as a model transglucosylation reaction. Hydrolysis to glucose was a side reaction. The selectivity towards transglucosylation was quantified by the S value defined as follows: S = r(S) x a(W)/r(H) x a(hex) where r(S) and r(H) are the initial rates of transglucosylation and hydrolysis and a(w) and a(hex) are the thermodynamic activities of water and hexanol. The activity (rates of hydrolysis and transglucosylation) and the selectivity (S value) were measured as a function of pentyl-beta-glucoside concentration (5-240 mM), water content (1-100% v/v), and temperature (50-95 degrees C). All mutants had lower activity than the wild-type enzyme, but they had higher selectivity, which means that they provided a higher ratio of transglucosylation product to hydrolysis product. The largest increase in S-value (2.6 fold) was obtained by the F426Y mutant, which resulted in increased hexyl-beta-glucoside yield from 56% to 69%. In addition, the F426Y enzyme had higher selectivity over the wide range of temperatures tested. The activity of CelB wild-type and CelB F426Y increased as a function of water activity (a(w)), and complete activation by the water was obtained in a two-phase system with 20% water phase. In contrast to CelB wild-type, the F426Y mutant had transferase activity as low as a(w) = 0.29. Surprisingly, the S value increased with increasing water activity up to a(w) = 0.92. At still higher water content the S value decreased.

Improved oligosaccharide synthesis by protein engineering of beta-glucosidase CelB from hyperthermophilic Pyrococcus furiosus.

Enzymatic transglycosylation of lactose into oligosaccharides was studied using wild-type beta-glucosidase (CelB) and active site mutants thereof (M424K, F426Y, M424K/F426Y) and wild-type beta-mannosidase (BmnA) of the hyperthermophilic Pyrococcus furiosus. The effects of the mutations on kinetics, enzyme activity, and substrate specificity were determined. The oligosaccharide synthesis was carried out in aqueous solution at 95 degrees C at different lactose concentrations and pH values. The results showed enhanced synthetic properties of the CelB mutant enzymes. An exchange of one phenylalanine to tyrosine (F426Y) increased the oligosaccharide yield (45%) compared with the wild-type CelB (40%). Incorporation of a positively charged group in the active site (M424K) increased the pH optimum of transglycosylation reaction of CelB. The double mutant, M424K/F426Y, showed much better transglycosylation properties at low (10-20%) lactose concentrations compared to the wild-type. At a lactose concentration of 10%, the oligosaccharide yield for the mutant was 40% compared to 18% for the wild-type. At optimal reaction conditions, a higher ratio of tetrasaccharides to trisaccharides was obtained with the double mutant (0.42, 10% lactose) compared to the wild-type (0.19, 70% lactose). At a lactose concentration as low as 10%, only trisaccharides were synthesized by CelB wild-type. The beta-mannosidase BmnA from P. furiosus showed both beta-glucosidase and beta-galactosidase activity and in the transglycosylation of lactose the maximal oligosaccharide yield of BmnA was 44%. The oligosaccharide yields obtained in this study are high compared to those reported with other transglycosylating beta-glycosidases in oligosaccharide synthesis from lactose.

Hydrolytic and transphosphatidylation activities of phospholipase D from Savoy cabbage towards lysophosphatidylcholine.

The hydrolysis and transphosphatidylation of lysophosphatidylcholine (LPC), with a partially purified preparation of phospholipase D (PL D) from Savoy cabbage, was investigated. These reactions were about 20 times slower than the hydrolysis of phosphatidylcholine (PC) in a micellar system. For the transfer reaction, 2 M glycerol was included in the media, which suppressed the hydrolytic reaction. Both reactions presented similar V(max) values, suggesting that the formation of the phosphatidyl-enzyme intermediate is the rate-limiting step. The enzyme had an absolute requirement for Ca(2+), and the optimum concentration was approximately 40 mM CaCl(2). K(Ca)(app) was calculated to be 8.6+/-0.74 mM for the hydrolytic and 10+/-0.97 mM for the transphosphatidylation reaction. Both activities reached a maximum at pH 5.5, independent of Ca(2+) concentration. Kinetic studies showed that the Km(app) for the glycerol in the transphosphatidylation reaction is 388+/-37 mM. Km(app) for the lysophosphatidylcholine depended on Ca(2+) concentration and fell between 1 and 3 mM at CaCl(2) concentrations from 4 to 40 mM. SDS, TX-100, and CTAB did not activate the enzyme as reported for phosphatidylcholine hydrolysis; on the contrary, reaction rates decreased at detergent concentrations at or above that of lysophosphatidylcholine.

Mutants provide evidence of the importance of glycosydic chains in the activation of lipase 1 from Candida rugosa.

Sequence analysis of Candida rugosa lipase 1 (LIP1) predicts the presence of three N-linked glycosylation sites at asparagine 291, 314, 351. To investigate the relevance of sugar chains in the activation and stabilization of LIP1, we directed site mutagenesis to replace the above mentioned asparagine with glutamine residues. Comparison of the activity of mutants with that of the wild-type (wt) lipase indicates that both 314 and 351 Asn to Gln substitutions influence, although at a different extent, the enzyme activity both in hydrolysis and esterification reactions, but they do not alter the enzyme water activity profiles in organic solvents or temperature stability. Introduction of Gln to replace Asn351 is likely to disrupt a stabilizing interaction between the sugar chain and residues of the inner side of the lid in the enzyme active conformation. The effect of deglycosylation at position 314 is more difficult to explain and might suggest a more general role of the sugar moiety for the structural stability of lipase 1. Conversely, Asn291Gln substitution does not affect the lipolytic or the esterase activity of the mutant that behaves essentially as the wt enzyme. This observation supports the hypothesis that changes in activity of Asn314Gln and Asn351Gln mutants are specifically due to deglycosylation.

Lysophosphatidylcholine synthesis with Candida antarctica lipase B (Novozym 435).

Immobilized lipase from Candida antarctica lipase B (Novozym 435) was effective in the synthesis of lysophosphatidylcholine (LPC). The transesterification of L-alpha-glycerophosphorylcholine (GPC) and vinyl laurate was carried out in a solvent free system or in the presence of 50% (v/v) t95%) were easily achieved. The lipase was selective for the sn10 times). High purity products could be produced by a decrease of the reaction temperature to induce precipitation of the product. The temperature needed depended on the fatty acid chain length. Thus, only lysophosphatidylcholine was produced with palmitic acid vinyl ester at 45 degrees C, whereas for the vinyl esters of lauric acid, capric acid, and caprylic acid, a lower reaction temperature (25 degrees C) was necessary to obtain solely the lysophospholipid products.

Two-enzyme system for the synthesis for 1-lauroyl-rac-glycerophosphate (lysophosphatidic acid) and 1-lauroyl-dihydroxyacetonephosphate.

A combination of two enzymes, phospholipase D (PL D) and C (PL C), was investigated for the production of two lysophospholipids, 1-lauroyl-rac-glycerophosphate (1-LGP) and 1-lauroyl-dihydroxyacetonephosphate (1-LDHAP). The high transphosphatidylation ability of phospholipase D from Streptomyces sp. allowed the formation of 1-lauroyl-phosphatidylglycerol (1-LPG) and 1-lauroyl-phosphatidyldihydroxyacetone (1-LPDHA) from phosphatidylcholine (PC) and 1-monolauroyl-rac-glycerol (1-MLG) and 1-lauroyl-dihydroxyacetone (1-MDHA), respectively. A two-phase system, diethyl ether/water, was chosen for the convenience of the recovery of the water insoluble products. A similar two-phase system was used for hydrolysis of the complex phospholipids by phospholipase C form Bacillus cereus, which released both lysophospholipids. Only trace amounts of phosphatidic acid (PA) were detected showing that the enzyme is highly selective for the release of the diacylglycerol and 1-lauroyl-rac-glycerophosphate and 1-lauroyl-dihydroxyacetonephosphate.

Enzymatic fatty acid exchange in digalactosyldiacylglycerol.

Six different lipases were screened for their ability of acidolysis between digalactosyldiacylglycerol (DGDG) and heptadecanoic acid in toluene. Lipases from Geotrichum candidum, Alcaligenes sp. and Penicillium camembertii did not catalyse the acidolysis reaction. Rhizopus arrhizus and Rhizomucor miehei (Lipozyme) catalysed the acidolysis but produced a mixture of DGMG, DGDG, acyl-DGMG and acyl-DGDG. The extra acyl group is bound to the primary hydroxyl of the digalactosyl moiety. Candida antarctica also catalysed the acidolysis but the TLC analysis showed bands with higher Rf values than acyl-DGDG, these probably being different tetra and higher esters. R. arrhizus lipase was the most promising enzyme under the conditions used, with no tetra esters being formed and giving the highest reaction rate of the enzymes investigated. Low water activity (0.06 or 0.11) and high fatty acid concentration (400 mM) increased the formation of acyl-DGDG whilst higher water activities (0.33 and 0.54) increased the amount of DGMG when R. arrhizus lipase was used as catalyst. At a water activity of 0.11 and a fatty acid concentration of 400 mM a yield of 24% modified DGDG was obtained. In this product the fatty acid originally present in the sn-1 position had been exchanged by heptadecanoic acid.

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

The selectivity of preparations of alpha-chymotrypsin immobilized on Celite or polyamide and carrying out syntheses of di- and tripeptides in acetonitrile medium were studied. The study concerns the effect of mass-transfer limitations on three different kinds of selectivity: acyl donor, stereo- and nucleophile selectivities, defined respectively as the ratio of initial rates with different acyl donors; the enantioselectivity factor (E); and the ratio of initial rates of peptide synthesis and hydrolysis of the acyl donor. Strong mass-transfer limitations caused by increased enzyme loading had a very strong effect on acyl donor selectivity, with reductions of up to 79%, and on stereoselectivity, with reductions of up to 77% in relation to optimum values, both on Celite. Nucleophile selectivity was not affected as strongly by mass-transfer limitations. Using a small molecule (AlaNH(2)) as nucleophile, the onset of these limitations caused only minor reductions in selectivity, while when using a larger nucleophilic species (AlaPheNH(2)) it was reduced by up to 60% when increasing enzyme loading on Celite from 2 to 100 mg/g. The different way these kinds of selectivity are affected by the onset of mass-transfer limitations can be explained by a combination of different aspects: the kinetic behavior of the enzyme toward nucleophile and acyl donor concentrations, the relative concentrations of reagents used in the reaction media, and their relative diffusion coefficients. In short, higher concentrations of nucleophile than acyl donor are generally used, and the nucleophile most often used in the experiments hereby described (AlaNH(2)) diffuses faster than the acyl donors employed. These factors combined are expected to give rise to concentration gradients inside porous biocatalyst particles higher for acyl donor than for nucleophile under conditions of mass-transfer limitations. This explains why acyl donor selectivity and stereoselectivity are much more influenced by mass transfer limitations than nucleophile selectivity.

Thermodynamic and kinetic aspects on water vs. organic solvent as reaction media in the enzyme-catalysed reduction of ketones.

The stereoselective reduction of ketones catalysed by alcohol dehydrogenase from Thermoanaerobium brockii was studied in different reaction media, hexane at controlled water activities, hexane with 2. 5% water (biphasic) and pure water. The reactions were studied in the temperature range from -1 to 50 degrees C. Increasing the water activity from 0.53 to 0.97 increased the reaction rate 16-fold. The rate was further enhanced in hexane when exceeding the water solubility and in pure water the rates were even higher. This was general for all ketones studied. At controlled water activity the entropy of activation (DeltaSdouble dagger) was the dominating factor. Large negative DeltaSdouble dagger values caused low reaction rates at low aw. When increasing the carbon chain length of the substrate, for reactions in hexane, the decrease of reaction rate was mainly due to a decrease in DeltaSdouble dagger. In the comparison between hexane and pure water, DeltaGdouble dagger values were higher in hexane due to higher DeltaHdouble dagger (activation enthalpy) values. The enantioselectivity (E value) increased from 2.6 at water activity 0. 53 to 4.6 at water activity 0.97. Changing media from hexane (2.5%, v/v water) to pure water was not affecting the enantioselectivity or the specificity for different ketones.

Reaction medium engineering in enzymatic peptide fragment condensation: synthesis of eledoisin and LH-RH.

The influence of different reaction systems on alpha-chymotrypsin-catalyzed synthesis of eledoisin and LH-RH peptides from (7 + 4) and (5 + 5) fragments was investigated. The peptide yield was determined in the following systems: buffered aqueous media, frozen solutions, organic media, and cosolvent mixtures. The experimental set up was tailored to allow the screening of an array of conditions with minimum consumption of peptide fragments (2.1 and 2.5 mM). The best yields (22% yield for eledoisin and 68% yield for LH-RH) were obtained in buffered aqueous solutions. It was found that the choice of buffer had a strong influence on the peptide yield; boric-borate and ammonium acetate buffers at pH 9, gave the best results. In buffered aqueous systems, both syntheses were scaled up by using a 10-fold increase in fragment concentration (21 and 25 mM). Under these conditions the yields rose to 57% and 80% of eledoisin and LH-RH, respectively. Moreover, during the synthesis of eledoisin and in the presence of boric-borate buffer pH 9, the peptide precipitated from the reaction medium preventing a secondary hydrolysis and facilitating the in situ product purification.

Evaluation of Alcaligenes eutrophus cells as an NADH regenerating catalyst in organic-aqueous two-phase system.

A soluble NAD-dependent hydrogenase contained in Alcaligenes eutrophus was evaluated as a coenzyme regenerating catalyst in an organic-aqueous two-phase (predominantly organic) system. The horse-liver alcohol-dehydrogenase (HLADH) catalyzed reduction of cyclohexanone to cyclohexanol was used as a model reaction. The impact of different solvents (selected to span a large variety of principal properties) on the stability and activity of the HLADH, using substrate-driven regeneration, was studied. Solvents suitable for the HLADH were then selected for an evaluation of the hydrogenase-driven coenzyme regeneration. Hydrophobic solvents such as heptane, toluene, and 1,1,1-trichloroethane were found to be suitable for the coupled reactions catalyzed by HLADH and hydrogenase. Nonimmobilized cells, permeabilized with cetyl-trimethyl-ammonium bromide, were the most efficient preparation for the regeneration of NADH. The use of this preparation in heptane (10% water) was optimized with respect to the yield obtained in the HLADH-catalyzed reduction of cyclohexanone. Using the optimized conditions, yields of 99% cyclohexanol were obtained.

Mass transfer studies on immobilized alpha-chymotrypsin biocatalysts prepared by deposition for use in organic medium.

Mass transfer limitations were studied in enzyme preparations of alpha-chymotrypsin made by deposition on different porous support materials such as controlled pore glasses, Celite, and polyamides of different particle sizes. It is the onset of mass transfer limitations that determines the position of the activity optimum with respect to enzyme loading on each support. The evidence of various experiments indicates that internal diffusional limitations are the important mechanism for the observed mass transfer limitations. External diffusion was not found to play an important role under the conditions used, and it was also found that when immobilizing multilayers of enzyme the buried enzyme molecules are active to a large extent. An extreme situation is observed on Celite at very high loadings. Under these conditions, this support is expected to have its pores completely filled with packed enzyme molecules, and then it is the diffusion within the enzyme layer that determines the observed rate. As the enzyme loading increases, the area of contact between the deposited enzyme layers and the liquid solution inside the pores diminishes, causing a decrease on the observed rate of an intrinsically fast reaction which apparently is incongruous with the presence of more enzyme in the system. This work shows that mass transfer limitations can be an important factor when working with immobilized enzymes in organic media, and its study should be carried out in order to avoid undesired reduced enzyme activities and specificities.

The enantiomeric purity of alcohols formed by enzymatic reduction of ketones can be improved by optimisation of the temperature and by using a high co-substrate concentration.

The stereoselective reduction of ketones by alcohol dehydrogenase from Thermoanaerobium brockii was studied in organic reaction media. 2-Propanol was used as co-substrate to regenerate the coenzyme NADPH. The enantiomeric excess of the alcohol formed from the ketone decreased during the course of the reaction (from 53 to 0% e.e. in the formation of (R)-2-butanol). This was interpreted as being due to the reversibility of all the reactions involved. By using a large excess of 2-propanol this effect was suppressed. In the reduction of 2-butanone to (R)-2-butanol, the enantiomeric excess increased with increasing temperature, but in the reduction of 2-pentanone to (S)-2-pentanol the enantiomeric excess decreased with increasing temperature. The data were evaluated in terms of free energy of activation of the reaction pathways leading to the different possible products.

Adsorption of lipase on polypropylene powder.

Adsorption of different lipases by EP-100 polypropylene powder from crude and pure lipase preparations was studied. Langmuir isotherms described the adsorption equilibria well both for protein and lipase activity adsorption. Adsorption isotherms for five different proteins all gave a similar saturation level of 220 mg protein per g carrier. Twelve commercial lipase preparations were tested for selectivity in the adsorption of lipase. For all preparations the selectivity factor was larger than one. In a crude lipase preparation from Pseudomonas fluorescence, the specific activity in solution decreased by two orders of magnitude after adsorption. The adsorption was not significantly influenced by pH changes in the adsorption buffer, indicating that hydrophobic and not electrostatic interactions are the dominating adsorption forces. Adsorption of a crude lipase from Candida rugosa (Sigma) was fast and equilibrium was reached in 30 and 100 min for protein and lipase activity adsorption respectively. Desorption in aqueous solution was negligible. Investigations with seven different lipases showed no correlation between the specific lipolytic activity of dissolved enzyme in aqueous solution and the specific activity of adsorbed enzyme in an esterification reaction in organic solvent.

How do additives affect enzyme activity and stability in nonaqueous media?

The catalytic activities of lyophilized powders of alpha-chymotrypsin and Candida antarctica lipase were found to increase 4- to 8-fold with increasing amounts of either buffer salts or potassium chloride in the enzyme preparation. Increasing amounts of sorbitol in the chymotrypsin preparation produced a modest increase in activity. The additives are basically thought to serve as immobilization matrices, the sorbitol being inferior because of its poor mechanical properties. Besides their role as supports, the buffer species were indispensable for the transesterification activity of chymotrypsin because they prevented perturbations of the pH during the course of the reaction. Hence, increasing amounts of buffer species yielded a 100-fold increase in transesterification activity. Effects of pH changes were not as predominant in the peptide synthesis and the lipase-catalyzed reactions. Immobilization of the protease on celite resulted in a remarkable improvement of transesterification activity as compared to the suspended protease, even in the absence of buffer species. Immobilization of the lipase caused a small improvement of activity. The activity of the immobilized enzymes was further enhanced 3-4 times by including increasing amounts of buffer salts in the preparation.The inclusion of increasing amounts of sodium phosphate or sorbitol to chymotrypsin rendered the catalyst more labile against thermal inactivation. The denaturation temperature decreased with 7 degrees C at the highest content of sodium phosphate, as compared to the temperature obtained for the denaturation of the pure protein. The apparent enthalpy of denaturation increased with increasing contents of the additives. The enhancement of hydration level and flexibility of the macromolecule upon addition of the compounds partly provides the explanation for the observed results.

Water activity and substrate concentration effects on lipase activity.

Catalytic activity of lipases (from Rhizopus arrhizus, Canadida rugosa, and Pseudomonas sp. was studied in organic media, mainly diisopropyl ether. The effect of water activity (a(w)) on V(max) showed that the enzyme activity in general increased with increasing amounts of water for the three enzymes. This was shown both for esterification and hydrolysis reactions catalyzed by R. arrhizus lipase. In the esterification reaction the K(m) for the acid substrate showed a slight increase with increasing water activities. On the other hand, the K(m) for the alcohol substrate increased 10-20-fold with increasing water activity. The relative changes in K(m) were shown to be independent of the enzyme studied and solvent used. The effect was attributed to the increasing competition of water as a nucleophile for the acyl-enzyme at higher water activities. In a hydrolysis reaction the K(m) for the ester was also shown to increase as the water activity increased. The effect of water in this case was due to the fact that increased concentration of one substrate (water), and thereby increased saturation of the enzyme, will increase the apparent K(m) of the substrate (ester) to be determined. This explained why the hydrolysis rate decreased with increasing water activity at a fixed, low ester concentration. The apparent V(max) for R. arrhizus lipase was similar in four of six different solvents that were tested; exceptions were toulene and trichloroethylene, which showed lower values. The apparent K(m) for the alcohol in the solvents correlated with the hydrophobicity of the solvent, hydrophobic solvents giving lower apparent K(m). (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 798-806, 1997.

Characterization and optimization of phospholipase A2 catalyzed synthesis of phosphatidylcholine.

The phospholipase A2 (PLA2) catalyzed synthesis and hydrolysis of phosphatidylcholine (PC) was studied in a water activity controlled organic medium. The aim of the study was to find the conditions most favorable for the synthetic reaction. To do this, the impact of various parameters such as water activity, substrate concentration and temperature on enzyme activity and equilibrium yield was determined. The PC to lysophosphatidylcholine (LPC) ratio at equilibrium increases with decreasing water activity and increasing fatty acid concentration, as can be expected from the law of mass action of an esterification reaction. The enzyme activity on the other hand decreases under conditions that favor the esterification. The best yield in the synthetic reaction is 60% at a water activity of 0.11 and an oleic acid concentration of 1.8 M. That is to our knowledge the highest yield ever reported in this reaction. Both the hydrolysis and synthesis reaction follow Michaelis-Menten kinetics, the apparent Km values are the same for PC and LPC, namely 4.9 mM. Vmax is 82.5 and 10.4 nmol h(-1) mg(-1) for the hydrolysis and synthesis reaction, respectively. Studies on PLA2 at water activity controlled conditions resulted in a more complete understanding of the enzymatic reaction and allowed to find the conditions most favorable for the synthetic reaction.