Journal of Molecular Catalysis B-enzymatic最新文献

Three new metabolites were obtained on incubation of androgenic steroid mesterolone (1) with Cunninghamella blakesleeana. These metabolites were identified as 1α-methyl-11β,14α,17β-trihydroxy-5α-androstan-3-one (2), 1α-methyl-7β,17β-dihydroxy-5α-androstan-3-one (3), and 1α-methyl,17β-hydroxy-5α-androstan-3,7-dione (4). During this study, hydroxylation at C-11, C-14, and C-15, and oxidation at C-7 of substrate 1 were observed. β-Hydroxylation at C-11 is a rather unique transformation by C. blakesleeana, as α-hydroxylation is reported to be catalyzed by most of the other microorganisms.

Product inhibition of β-glucosidase is considered as one of the central rate limiting steps as it starts accumulation of intermediates responsible for the slowdown of the cellulose hydrolysis. Feedback inhibitions exhibited by glucose and other oligosaccharides on the cellulose hydrolyzing enzyme reduces the rate of hydrolysis bringing the entire process to standstill. However, the exact mechanism of this catalytic slowdown is still elusive. In present study, β-glucosidases were investigated for their activities under high glucose and cellobiose concentrations. β-glucosidases recognizes cellobiose a true substrate and hydrolyzes it resulting in glucose or transglycosylates it to give cellotriose. Our observation highlight that rates of reaction for cellotriose synthesis and glucose formation are mainly concentration driven and are dynamically adjusted based on cellobiose concentration in the reaction system. We therefore conclude that critical concentration of DP2: DP3 influences hydrolysis or transglycosylation and any modulation to this ratio influences the dynamics of β-glucosidases hydrolysis.

Inulin is a type of fructose polymer that is commonly present in plants as a storage carbohydrate. Enzymatic hydrolysis of inulin via exo-inulinase to produce fructose is an efficient, green and state-of-the-art technique. To achieve the high-level secretory expression of inulinase and to realize enzymatic preparation of fructose syrup from inulin, an Aspergillus exo-inulinase gene inu was codon-optimized and co-expressed with the endoplasmic reticulum secretion protein in Pichia cells. After inducible expression in a 500-L pilot scale bioreactor, the inulinase activity of the recombinant strains reached 10,480 U/mL of cultivation broth. Next, according to the determined enzymatic characteristics of inulinase INU, we optimized the parameters for inulinase to hydrolyse inulin. Under the optimal condition of the enzyme/inulin ratio of 5000 U/g, 15% substrate and an incubation temperature of 50 °C for 4 h, the hydrolysis ratio of inulin reached 100%. The hydrolysis products of inulin contain two components, 95% fructose, and 5% glucose. This study has fulfilled the scaled-up production of inulinase and facilitated its industrial application for enzymatic preparation of fructose from inulin.

A blackberry-shaped Fe₃O₄@SiO₂ nanoparticles were prepared, characterized and applied in covalently binding catalase. The enzyme loading decreased with the increase of pH, however, the activity recovery increased simultaneously. To elucidate the influence factor of the activity recovery, the enzyme loading was further regulated by changing the initial free enzyme content. The relationship between enzyme loading and activity recovery showed the consistent trend, whether the variation of enzyme loading was incurred by pH or by initial enzyme content. The simulated parameters showed the similar values according to the experiment at different conditions. It was concluded that activity recovery was dominated by protein density on surface, not by the orientation of the enzyme on surface, due to the negligible diffusion limit for H₂O₂ as the substrate of catalase. The immobilized catalase at pH 7.0 has a high activity recovery of 100% at 14.4 enzyme μg/mg nanoparticles. The K_m and V_max of the immobilized enzyme above are 0.215 mol and 0.797 mol/min, similar to 0.167 mol and 0.727 mol/min for the free enzyme, respectively.

In order to remove the residual lactose in crude galacto-oligosaccharides (GOS), different commercial soluble β-galactosidases from Kluyveromyces lactis (Lactozym Pure 6500L, Maxilact L2000, Lactase NL and Biolactasa-NL) and reaction conditions (temperature, total carbohydrate concentration and enzyme:substrate mass ratio) were evaluated. To select the best biocatalyst, the hydrolytic activity on o-NPG and thermal stability of all enzymes were evaluated in the absence and presence of three cations (Co²⁺, Mg²⁺, Mn²⁺) at different concentrations. The enzyme source, cation and cation concentration were selected to obtain the highest hydrolytic activity and thermal stability. Then lactose hydrolysis of raw GOS was assessed varying the temperature (30 °C–45 °C), total carbohydrate concentration (10%-50%) and enzyme:substrate mass ratio (50 IU g⁻¹–400 IU g⁻¹) and considering the lactose percentage decrease as response parameter (D_L). Lactase NL was selected as the best enzyme, with a hydrolytic activity of 286 IU mg⁻¹ and a half-life of 9 h at 35 °C in the presence of 1 mM Mn²⁺. The best reaction conditions for lactose hydrolysis employing the selected enzyme were 35 °C, 50% initial carbohydrate concentration and 135 IU g⁻¹. At such conditions of lactose hydrolysis, 70% reduction of lactose in raw GOS was obtained, with an increase of 48% in monosaccharides and of 30% in GOS. This pre-hydrolytic step is a key aspect for the subsequent purification of GOS by nanofiltration or selected bioconversion, in which monosaccharides can be removed efficiently producing GOS of high purity.

In this study, we developed an efficient approach for hydrophobic amino acids polymerization in aqueous solution. We compared the catalysis efficiency of papain and bromelain in catalyzing l-phenylalanine methyl ester (l-Phe-Me) for oligomer peptides synthesis. A set of reaction conditions (such as protease type, reaction temperature, time, and pH) have been tested for the polymerization reaction with papain and bromelain, respectively. Moreover, the resultant oligomers were analyzed through ¹HNMR and MALDI-TOF. The results indicated that the average degree of polymerization (DP) reached the highest value (6.74) when papain was used for l-Phe-Me polymerization in phosphate buffer (0.2 M, pH 8) at 40 °C for three hours. At 50 °C, the DP reached 6.62 with a yield of 72.9% when papain as the catalyst. Its yield and DP were 4.50 and 1.27 folds higher than those of the oligo- peptides synthesized by bromelain. Moreover, we found the DP and the yield of oligo(l-Phe) can be enhanced with higher reaction temperature and longer reaction time. In summary, papain presents better catalytic properties compared with bromelain for l-Phe polymerization in terms of DP and yield. Oligomerization catalyzed by papain at high temperature presents a potent procedure for the synthesis of biologically active oligo(l-Phe) peptides.

A major drawback to the industrial production of β-cyclodextrin is the limited β-cyclization activity of cyclodextrin glycosyltransferase (CGTase). Here, we construct mutants of the β-CGTase from Bacillus circulans strain STB01 that contain single substitutions at Tyr89 and double substitutions at Tyr89 and Asp577. The results show that the double mutants Y89G/D577R, Y89D/D577R, and Y89N/D577R display enhanced β-cyclization activity, and have higher β-cyclization activity than that of the three single Tyr89 mutants. The double mutant Y89D/D577R exhibited the highest β-cyclization activity and β-cyclodextrin production, increasing 35.1% and 12.4% compared with those of the wild-type CGTase, respectively. The β-cyclization activity of double mutant Y89D/D577R is also higher than that of the single mutant D577R, which had the highest β-cyclization activity among the mutants prepared in our previous studies. The enhanced β-cyclization activity of these mutants may be a result of intermolecular interactions that stabilize intermediates in the β-cyclization reaction. Thus, double mutant Y89D/D577R is much more suitable for industrial β-cyclodextrin production than the wild-type enzyme.

Here, we report regioselectively functionalized synthesis, as well as photo physical, electrochemical, and thermal, of a novel water-soluble conjugated polymer. For this purpose, horseradish peroxidase (HRP)-catalyzed polymerization of a multifunctional monomer, 7-amino-4-hydroxy-2-naphthalene sulfonic acid (AHNAPSA) was carried out by using hydrogen peroxide as the oxidant at room temperature for 24 h under air. The structure of poly(7-amino-4-hydroxy-2-naphthalene sulfonic acid), (PAHNAPSA) was identified by using nuclear magnetic resonance, infrared and ultraviolet-visible. Further characterization was performed by means of gel permeation chromatography (GPC), thermogravimetry (TG), differential scanning calorimetry (DSC), cyclic voltammetry (CV), photoluminescence (PL), dynamic light scattering (DLS) and solid state conductivity measurements. The spectral analysis results exhibited functional group selective polymerization of the monomer containing a multi-active center. Solvent effects on the optical, electrochemical and photo physical properties of PAHNAPSA were investigated by using five different solvents. PAHNAPSA presented an irreversible redox characterization at different scan rates. Optical band gap of PAHNAPSA is also found in the range of 3.18 eV to 3.55 eV. The fluorescence measurements were utilized to investigate the photochemical behaviors of PAHNAPSA in selected polar solvents. Accordingly, PAHNAPSA surprisingly presented multicolor emission behavior with relatively high quantum yield in all selected solvents. In addition, PAHNAPSA presented a reversible pH-responsive behavior and also had high selectivity and sensitivity towards chromium ions. Finally, the kinetic parameters associated with the solid state thermal degradation of PAHNAPSA were calculated from isoconversional methods. The TG/DTG analysis showed that PAHNAPSA followed a diffusion controlled degradation mechanism in N₂.

The direct hydration of CC bonds to yield alcohols or the reverse dehydration is chemically challenging but highly sought after. Recently, oleate hydratases (OAHs) gained attention as biocatalytic alternatives capable of hydrating isolated, non-activated CC bonds. Their natural reaction is the conversion of oleic acid to (R)-10-hydroxystearic acid.

In this work, we report the first comparative study of several OAHs. Therefore we established the Hydratase Engineering Database (HyED) comprising 2046 putative OAHs from eleven homologous families and selected nine homologs for cloning in E. coli. The heterologously expressed enzymes were evaluated concerning activity and substrate specificity. The enzymes have a broad substrate scope ranging from oleic acid (C18) to the novel synthetic substrate (Z)-undec-9-enoic acid (C11). The OAHs from Elizabethkingia meningoseptica and Chryseobacterium gleum showed the best expression, highest stability and broadest substrate scope, making them interesting candidates for directed evolution to engineer them for the application as general hydratase catalysts.

The immobilization of Candida rugosa lipase by adsorption was performed onto commercial titania powder (Degussa P25). The change of titania particles surface was diagnosed by means of FTIR and FESEM analysis, as well as by shift of zeta potential value towards that of lipase. A detailed study of the effect of immobilization on enzyme kinetic, temperature stability, as well as on potential for its reuse in aqueous organic media was undertaken. Immobilization of lipase altered enzyme affinity toward substrates with different length of carbon chain in hydrolytic reaction. The Vmax value decreased 2–8-fold, where major constraint was registered for the ester containing the longest carbon chain. Thermostability of lipase improved more than 7-fold at 60 °C. Significant potential for reuse in water solutions was also found after immobilization. In cyclohexane immobilized lipase catalyzed synthesis of amyl octanoate by ping-pong bi–bi mechanism with inhibition by amyl alcohol. Obtained kinetic constants were Vmax = 26.4 μmol min⁻¹, K_Ac = 0.52 mol/L, K_Al = 0.2 mol/L and K_i,Al = 0.644 mol/L. Esterification activity remained 60% after 5 reuse cycles in cyclohexane indicating moderate reuse stability.