Journal of Molecular Catalysis B-enzymatic最新文献

This study kinetically characterized the mechanism of the enzymatic synthesis of theaflavins (TFs) from catechins by mushroom tyrosinase (EC 1.14.18.1). In reactions containing one of four catechins, (-)-epicatechin (EC), (-)-epigallocatechin (EGC), and their galloylated forms (ECg and EGCg), they were oxidized by tyrosinase with apparent K_M values of 3.78, 5.55, 0.80, and 3.05 mM, respectively, and with different consumption rates, of which EC was more than four times higher than those of the others. In reactions with binary combinations of catechins with tyrosinase, the synthesis of TF1 from EC and EGC occurred most efficiently, while the yields of mono- and di-galloylated TFs, TF2A, TF2B, and TF3, were low. Time-dependent changes in concentrations of the reactants suggested that the enzymatic oxidation of catechins and the subsequent non-enzymatic coupling redox reaction between the quinone derived from EC or ECg and the intact pyrogallol-type catechin (EGC or EGCg) proceeded concurrently. The latter reaction induced the rapid decrease of EGC and EGCg and it was remarkable for EGCg. So the efficiency of condensation of a pair of quinones from catechol- and pyrogallol-type catechins is restricted, critically influencing the yield of TFs. Using green tea extracts as mixtures of the four substrate catechins, tyrosinase produced TF1 most abundantly. Furthermore, a remarkable enhancement of production of TF2A and TF2B as well as TF1 was observed, when the initial concentration of EGCg was low. These results suggest that the catechin composition has an impact on yields of TFs.

In this study, the catalytic efficiency using NitA from Acidovorax facilis 72W for nicotinic acid (NA) production was investigated and further improved by site-directed mutagenesis. Results showed that the specific activity of mutated NitA-C2 (F168V-S192F) towards 3-cyanopyridine increased 5-fold to 35 U mg⁻¹ protein. Further characterization of the biochemical properties of both nitrilases showed the optimal pH and temperature were 6.0–8.0 and 60 °C, respectively, whereas the pH and thermal stability of NitA-C2 were decreased. Finally, whole cell catalysis was adopted for NA production and a 100% conversion yield was achieved under 0.1 mol L⁻¹ 3-cyanopyridine for both strains. Besides, the conversion rate by E. coli BL21 (DE3-pET-nitA-C2) reached to 1.0 mmol min⁻¹ g⁻¹ wet cell weight, which was 3-fold higher than that by E. coli BL21 (DE3-pET-nitA). These results indicated that the mutated NitA-C2 was a promising candidate which holds potential application in biological NA production.

Both optically pure enantiomers of N-hydroxymethyl vince lactam are the key synthons for some important antiviral drugs. The high enantioselective transesterification of N-hydroxymethyl vince lactam was catalyzed by the lipase from Burkholderia ambifaria YCJ01 using vinyl acetate as the acyl donor. Under the optimized conditions, an efficient resolution of N-hydroxymethyl vince lactam in high substrate concentration (300 mM; 41.7 g/L) was obtained with nearly theoretical conversion yield of 50.1%, ee_p of 99% and ee_s of 99%. Strikingly, the highest enantioselectivity (E > 900) and dramatic increase of the lipase activity towards N-hydroxymethyl vince lactam were observed in a binary solvent system with hexane and MTBE (v/v = 1:9). The high substrate tolerance and enantioselectivity of lipase YCJ01 showed significant benefit in the practical resolution of racemic N-hydroxymethyl vince lactam. Additionally, the high enantiopreference of lipase YCJ01 towards (−)-N-hydroxymethyl vince lactam was also rationalized through molecular docking.

In this study, the methionine sulfoxide reductase A from a pseudomonas monteilii strain (pmMsrA) was reported to synthesize optically active sulfoxides (R)-1a-4a, through asymmetric biocatalytic reductive resolution. Several biotransformation parameters including the reaction time, cell density, and substrate concentration were optimized. Moreover, Substrate scope of pmMsrA catalyzed asymmetric reductive resolution was investigated, which gave chiral (R)-1a-4a with 61%-97% ee.

Alkaline proteases produced from protein-rich waste (hair waste and soya residues) by solid state fermentation (SSF) were immobilised onto functionalized magnetic iron oxide nanoparticles (MNPs) using glutaraldehyde as a crosslinking agent. The covalent binding method had a better immobilisation yield compared to simple adsorption, retaining 93%–96% (459 ± 106 U/mg nanoparticles, 319 ± 34 U/mg nanoparticles) of hair waste and soya residues proteases, respectively after crosslinking with 5% glutaraldehyde for 6 h. However, the adsorption immobilisation yield was 47%–54% after 8 h for both proteases. MNPs and immobilised proteases were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and electron diffraction. Our results indicated successful crosslinking between the proteases and amino-functionalized MNPs. The operational stability (pH and temperature) and storage stability of free and immobilised enzyme were also analysed. Despite the fact that the optimum pH of free and immobilised proteases was identical in the alkaline region, the immobilised proteases reached their optimum condition at higher temperatures (40 °C–60 °C). After 2 months of storage at 4 °C, the immobilised proteases showed good stability, retaining more than 85% of their initial activity. The high magnetic response of MNPs render an ease of separation and reusability, which contributes to the residual activity of both immobilised proteases on MNPs retaining more than 60% of their initial values after seven hydrolytic cycles. These results showed the enhancement of the stability of the crosslinking interactions between the proteases and nanoparticles. The immobilised proteases were capable of hydrolysing selected proteins (casein, oat bran protein isolate, and egg white albumin). However, differences in the degree of hydrolysis were observed, depending on the combination of the protease and type of substrate used.

6-Gingerol ((S)-5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-3-decanone), the major gingerol present in ginger rhizomes, has been found to prevent fat accumulation and improve blood flow. However, its low solubility in water and strong pungent odor often limit its potential applications such as in functional foods. In order to overcome these disadvantages, we investigated microbial glucosylation of 6-gingerol by the soil bacterium Ensifer sp. M-26. 5-O-α-Glucosylgingerol was found to be produced from a mixture of maltose and 6-gingerol by the action of washed cells of Ensifer sp. M-26. The addition of organic solvents, such as hexane, to the reaction mixture enhanced 5-O-α-glucosylgingerol production. When the microbial reaction was carried out with 1.3 g/L of 6-gingerol and 100 g/L of maltose under optimized conditions, 0.40 g/L of 5-O-α-glucosylgingerol was accumulated in 25 h. The molar yield of 5-O-α-glucosylgingerol was 19.9 mol%.

The xylanase gene (xynTF16) from a thermophilic bacterium Geobacillus sp. TF16 was cloned into pET-28a(+) vector and expressed in Escherichia coli BL21(DE3)pLysS. Recombinant enzyme (GsXynTF16) was purified 52-fold by nickel affinity chromatography, and determined as a single band 39.8 kDa on SDS-PAGE with a specific activity of 246 U/mg protein. The recombinant enzyme was immobilized on chitosan with a yield of 85.6%. The enzyme showed the highest activity towards xylan. The immobilized enzyme displayed an increase in optimum temperature from 55 to 65 °C in comparison with free enzyme. While the free enzyme was optimally active at pH 8.5, immobilized enzyme showed higher activity in the pH range 6.0–8.5. Thermal and pH stability of immobilized enzyme was determined to be higher than that of the free enzyme. Immobilized xylanase could be reused for 6 consecutive cycles retaining 80% of its initial activity. It was also found to be effective in releasing the reducing sugar from juice and poultry feed and oven spring in bakery. These results suggest that this study provides an alternative xylanase enzyme with enhanced properties.

An efficient, cost effective and environmentally friendly protocol has been developed for the Michael addition of malononitrile on 1,3-diaryl-2-propen-1-ones (Chalcones) using very cheaper, easily available natural catalyst, baker’s yeast. The whole cells of yeast excellently worked in nonaqueous medium, ethanol without decrease in catalytic activity.

The enzyme activity of α-chymotrypsin (ChT) has been known to increase with the addition of polyelectrolytes and amine compounds that combine with oppositely charged substrates. Enzyme hyperactivation is thought to occur by changing the electrostatic field around the enzyme, leading to favorable interactions between the enzyme and substrate. Inspired by the enzyme hyperactivation system, this paper focuses on inorganic salts as additives that specifically affect the enzyme activity of ChT toward the small, hydrophobic substrate phenylalanine-p-nitroanilide. The enzyme activity of ChT increased linearly with increasing concentration of kosmotropes; k_cat/K_M of ChT in the presence of 1.5 M sodium sulfate was 18-fold higher than in the absence of salts. In contrast, the enzyme activity of ChT was decreased by sodium perchlorate and sodium thiocyanate due to denaturation. Enzyme kinetic analysis showed that the increased activity of ChT caused by sodium sulfate results from both increasing k_cat and decreasing K_M. Kosmotropes enhanced both the structural stability of the native state and hydrophobic interactions between the enzyme and substrate. This simple yet effective enzyme activation mechanism provides biotechnological applications as well as new insight into the enzymology of ChT.