Journal of Molecular Catalysis B-enzymatic最新文献

Proline dehydrogenase (ProDH) is a ubiquitous flavoenzyme involved in the biosynthesis of l-glutamate. ProDH is of interest for biocatalysis because the protein might be applied in multi-enzyme reactions for the synthesis of structurally complex molecules. We recently demonstrated that the thermotolerant ProDH from Thermus thermophilus (TtProDH) is overproduced in Escherichia coli when using maltose-binding protein (MBP) as a solubility tag. However, MBP-TtProDH and MBP-clipped TtProDH are prone to aggregation through non-native self-association. Here we provide evidence that the hydrophobic N-terminal helix of TtProDH is responsible for the self-association process. The more polar MBP-tagged F10E/L12E variant exclusively forms tetramers and exhibits excellent catalytic features over a wide range of temperatures. Understanding the hydrodynamic and catalytic properties of thermostable enzymes is important for the development of industrial biocatalysts as well as for pharmaceutical applications.

The aim of this study was to investigate the effect of 3 different surface plasma treatments on the immobilization of β-galactosidase on a fibrous PET nonwoven membrane. Two methods 1. Entrapment in a thin calcium alginate coating and 2. Direct sorption, were used to immobilize the enzyme. The three different plasma treatments for surface activation of PET nonwovens were: 1. Air atmospheric DBD plasma, 2. Cold remote plasma-CRP with 100% N₂ and 3.- CRP with a mixture of N₂/O₂ gases. Plasma treatment of the PET fiber surface increased the quantity of immobilized enzyme using the entrapment method, and the degree of alginate film cross-linking highly influenced the enzyme activity. Highest enzyme activity was reached for the PET treated with air atmospheric plasma and cross-linked with 0.25 g/l of CaCl₂. With the direct sorption method, greater amounts of enzyme were immobilized as compared to the entrapment method, but a considerable proportion of enzyme lost their catalytic activity. Only with the CRP N₂/O₂ plasma treatment, up to 90% of sorbed enzyme maintained their activity. Reusability study showed that for the optimized entrapment method, a progressive decrease in activity was observed after each use cycle. With the optimized sorption method using N₂/O₂ CRP plasma, no decrease in enzyme activity was detected, and the immobilized enzyme could be used over more than 15 cycles.

α-l-Rhamnosidases (α-RHAs) are a group of glycosyl hydrolases of biotechnological potential in industrial processes, which catalyze the hydrolysis of α-l-rhamnose terminal residues from several natural compounds. A novel α–RHA activity was identified in the crude extract of Novosphingobium sp. PP1Y, a marine bacterium able to grow on a wide range of aromatic polycyclic compounds. In this work, this α-RHA activity was isolated from the native microorganism and the corresponding orf was identified in the completely sequenced and annotated genome of strain PP1Y. The coding gene was expressed in Escherichia coli, strain BL21(DE3), and the recombinant protein, rRHA-P, was purified and characterized as an inverting monomeric glycosidase of ca. 120 kDa belonging to the GH106 family. A biochemical characterization of this enzyme using pNPR as substrate was performed, which showed that rRHA-P had a moderate tolerance to organic solvents, a significant thermal stability up to 45 °C and a catalytic efficiency, at pH 6.9, significantly higher than other bacterial α-RHAs described in literature. Moreover, rRHA-P was able to hydrolyze natural glycosylated flavonoids (naringin, rutin, neohesperidin dihydrochalcone) containing α-l-rhamnose bound to β-d-glucose with either α-1,2 or α-1,6 glycosidic linkages. Data presented in this manuscript strongly support the potential use of RHA-P as a biocatalyst for diverse biotechnological applications.

Biocatalytic oxidations can offer clear advantages compared to chemically catalyzed oxidations in terms of chemo, regio and stereoselectivity as well as a reduced environmental impact. One of the most industrially important reactions is the oxidation of alcohols, which can be carried out using alcohol dehydrogenases. However, their effective use requires an effective regeneration of the oxidized nicotinamide cofactor (NAD(P)⁺), which is critical for the economic feasibility of the process. NAD(P)H oxidase is an enzyme class of particular interest for this cofactor regeneration since it enables the use of molecular oxygen as a substrate, generating either water or hydrogen peroxide as a by-product. The use of these enzymes is now gaining an increased interest, and several different enzymes of both types have been applied for proof-of-concept. In this review, we give an overview of the state-of-the-art, and discuss several important issues for future implementation in a production process.

Mannitol-2-dehydrogenase (MtDH) (E.C. 1.1.1.67) gene was cloned from Thermotoga neapolitana DSM 4359 and expressed in Escherichia coli BL21. The purified enzyme showed a predicted clear band of 36 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), native molecular mas was 135 kDa. K_m and V_max values for reduction of D-fructose to D-mannitol were 20 mM and 200 U mg-1 respectively. k_cat for reduction direction was 180 s⁻¹ and k_cat/K_m were 9 mM⁻¹ s⁻¹. The enzyme showed optimal pH at 6.5 and the optimum temperature was 90 °C with 100% relative activity. The purified enzyme was quite stable at 75 °C and had half of initial activity after 1 h of incubation at 90 °C. (TnMtDH) showed no activity with xylitol, inositol, sorbitol, rahmanose, mannose and xylose, and with NADPH and NADP⁺ as co factors. The presence of some divalent metals in the reaction enhanced the enzyme activity. The enzyme might be utilizing to produce mannitol without other sugar conformation under high temperature.

p-Hydroxyphenylacetate (HPA) can be derived from the biodegradation of lignin or from man-made compounds. The pathway involved for HPA degradation has been characterized for several species, but little is known on the degradation of HPA in Acinetobacter sp. In this report, the HPA degradation operon in A. baumannii TH was investigated using genome walking and PCR amplification to identify the genes encoded by the operon. The results showed that there are thirteen ORFs that are involved in this process and their arrangement in the operon of A. baumannii TH is different from that in the operons of other previously reported species. ORFs 8-12 show clear variation compared to orthologous genes from other species, particularly at ORF9 which encodes for succinic semialdehyde dehydrogenase (SSADH) that is absent in other species. The ssadh gene was overexpressed and the results confirmed that this enzyme is indeed succinate semialdehyde dehydrogenase. The results suggest that the final metabolites in this pathway are pyruvate and succinate, different from other species which have pyruvate and succinic semialdehyde as final products. Functional studies of the proteins encoded by ORF 8 and 10-12 have confirmed their roles in the HPA degradation pathway as an aldolase, a transporter protein, a hydroxylase and a reductase. Analysis of the sequence similarity network of enzymes encoded by ORFs 8-12 has revealed several interesting features. The designation of enzymes homologous to the oxygenase component of p-hydroxyphenylacetate 3-hydroxylase in the database should be reassigned, as they were mostly incorrectly assigned as acyl-CoA dehydrogenases. An understanding of the enzymatic reactions which convert aromatic compounds into pyruvate and succinate should be highly useful for future metabolic engineering for converting waste-derived aromatic compounds into useful biochemicals.

Both optical antipodes of the cis-isomers of osmundalactone, a hydroxypyranone natural product and core structure of the angiopterlactones, have been synthesized from acetylfuran in only three steps through a redox cascade utilizing oxidoreductases and transition metal catalysis in a concerted fashion. The key step in this fully catalytic strategy is the enzyme-mediated Achmatowicz reaction via selective furan oxygenation to furnish the pyran core structure.

Lipases from Candida antarctica (A and B) (CALA and CALB), Candida rugosa (CRL), Thermomyces lanuginosus (TLL) and Rhizomucor miehei (RML), as well as the chimeric phospholipase Lecitase Ultra (LU) were immobilized on octyl agarose or on heterofunctional octyl supports. RML, CRL and TLL were covalently immobilized on octyl agarose beads activated with divinyl sulfone (OCDVS), while the other lipases were immobilized on octyl-glyoxyl beads (OCGLX). The 12 biocatalysts were utilized in the production of esters using tributyrin and 20% (v/v) methanol, ethanol or isopropanol via a kinetically controlled strategy. All preparations produced the desired ester, except RML, TLL and LU for isopropyl butyrate. CALA showed the best performance in these reactions, with maximum yields over 40%. The immobilization on heterofunctional supports usually reduced the activity and even the maximum yields, although some exceptions were relevant (e.g., CALA or CALB in the production of ethyl butyrate). The effect of the nucleophile was also very different using the just physically adsorbed or the covalently immobilized preparations, some instances one preparation has as best substrate an alcohol while the best substrate was other alcohol using the other lipase preparation.

Using CALB as model enzyme, we have shown the advantages of the use of the covalent preparation. The increase of the alcohol permitted the increase in maximum ester yields. However, the combined presence of dibutyrin and alcohol prevented the reuse of OC-CALB due to the enzyme desorption, while the covalent preparation could be reused by 6 cycles.

L-arginase from Rummeliibacillus pycnus SK31.001 is newly discovered. A 906 bp complete open reading frame, which encodes a 301 amino acid protein, was identified using degenerate PCR and inverse PCR techniques. The arginase was found to have a conserved active site with 6 amino acid residues binding to 2 manganese ions: D123, H125, D228, D230, H100 and D127. Bioinformatics analysis revealed that R. pycnus arginase is a hexamer with a subunit molecular mass of 33 kDa and whole molecular mass of 195 kDa. R. pycnus arginase is thermostable with an optimal temperature of 80 °C and maintains 85% of its initial activity after 24 h of incubation at 40 or 50 °C. An arginase activity assay showed that R. pycnus arginase has an optimum pH of 9.5 and a preference for Mn²⁺. Using arginine as the substrate, the Michaelis-Menten constant (K_m) and catalytic efficiency (k_cat/K_m) were measured to be 0.212 mM and 2970 mM⁻¹s⁻¹, respectively. The biosynthesis yield of L-ornithine by the purified enzyme was 144.4 g/L, and the molar yield was 95.2%.