Now showing 1 - 10 of 18
  • Publication
    A comparison of two novel alcohol dehydrogenase enzymes (ADH1 and ADH2) from the extreme halophile Haloferax volcanii
    Haloarchaeal alcohol dehydrogenases are exciting biocatalysts with potential industrial applications. In this study, two alcohol dehydrogenase enzymes from the extremely halophilic archaeon Haloferax volcanii (HvADH1 and HvADH2) were homologously expressed and subsequently purified by immobilized metal-affinity chromatography. The proteins appeared to copurify with endogenous alcohol dehydrogenases, and a double Δadh2 Δadh1 gene deletion strain was constructed to prevent this occurrence. Purified HvADH1 and HvADH2 were compared in terms of stability and enzymatic activity over a range of pH values, salt concentrations, and temperatures. Both enzymes were haloalkaliphilic and thermoactive for the oxidative reaction and catalyzed the reductive reaction at a slightly acidic pH. While the NAD+-dependent HvADH1 showed a preference for short-chain alcohols and was inherently unstable, HvADH2 exhibited dual cofactor specificity, accepted a broad range of substrates, and, with respect to HvADH1, was remarkably stable. Furthermore, HvADH2 exhibited tolerance to organic solvents. HvADH2 therefore displays much greater potential as an industrially useful biocatalyst than HvADH1.
      502Scopus© Citations 36
  • Publication
    Isolation and Characterization of Recovered Starch from Industrial Wastewater
    The wastewater generated at a facility specialising in potato processing was found to contain high levels of insoluble potato starch. Several separation methods were employed to obtain maximum potato starch recovery from the industrial wastewater. Centrifugation was proved to be the most effective means of separation. Following potato starch recovery, a variety of chemical and physico-chemical properties were investigated. Potato starch quality and consistency were assessed and monitored across a 1 year period, between 2007 and 2008. Based on the various starch characteristics that were obtained, it was established that the recovered potato starch was of a high quality and is therefore suitable for subsequent processing, without the need of performing any pre-treatment. Properties including total starch, damaged starch, protein, lipid and amylose content, as well as gelatinisation and retrogradation, were evaluated and a high level of consistency throughout the course of 1 year was recorded.
      375Scopus© Citations 8
  • Publication
    Alternative mild route to the synthesis of 4-methylenecyclohex-2-enone, a key moiety of the anticancer compounds ottelione A and B
    Rare 4-methylenecyclohex-2-enone is prepared from a Diels-Alder methanesulfonate adduct and sodium iodide in acetone in up to 70% yield under mild conditions. This procedure is envisaged to be relevant to the synthesis of 4-methylenecyclo hex-2-enone analogues, structurally similar to the key functionality of cytotoxic otteliones and with potentially significant bioactivity.
      451Scopus© Citations 3
  • Publication
    Heterologous overexpression, purification and characterisation of an alcohol dehydrogenase (ADH2) from Halobacterium sp. NRC-1
    Replacement of chemical steps with biocatalytic ones is becoming increasingly more interesting due to the remarkable catalytic properties of enzymes, such as their wide range of substrate specificities and variety of chemo-, stereo- and regioselective reactions. This study presents characterization of an alcohol dehydrogenase (ADH) from the halophilic archaeum Halobacterium sp. NRC-1 (HsADH2). A hexahistidine-tagged recombinant version of HsADH2 (His-HsADH2) was heterologously overexpressed in Haloferax volcanii. The enzyme was purified in one step by immobilised Ni-affinity chromatography (IMAC). His-HsADH2 was halophilic and mildly thermophilic with optimal activity for ethanol oxidation at 4 M KCl around 60 °C and pH 10.0. The enzyme was extremely stable, retaining 80 % activity after 30 days. His-HsADH2 showed preference for NADP(H) but interestingly retained 60 % activity towards NADH. The enzyme displayed broad substrate specificity, with maximum activity obtained for 1-propanol. The enzyme also accepted secondary alcohols such as 2-butanol and even 1-phenylethanol. In the reductive reaction, working conditions for His-HsADH2 were optimised for acetaldehyde and found to be 4 M KCl and pH 6.0. His-HsADH2 displayed intrinsic organic solvent tolerance, which is highly relevant for biotechnological applications.
      379Scopus© Citations 8
  • Publication
    Characterization of alcohol dehydrogenase (ADH12) from Haloarcula marismortui, an extreme halophile from the Dead Sea
    Haloarchaeal alcohol dehydrogenases are of increasing interest as biocatalysts in the field of white biotechnology. In this study, the gene adh12 from the extreme halophile Haloarcula marismortui (HmADH12), encoding a 384 residue protein, was cloned into two vectors: pRV1 and pTA963. The resulting constructs were used to transform host strains Haloferax volcanii (DS70) and (H1209), respectively. Overexpressed His-tagged recombinant HmADH12 was purified by immobilized metal-affinity chromatography (IMAC). The His-tagged protein was visualized by SDS-PAGE, with a subunit molecular mass of 41.6 kDa, and its identity was confirmed by mass spectrometry. Purified HmADH12 catalyzed the interconversion between alcohols and aldehydes and ketones, being optimally active in the presence of 2 M KCl. It was thermoactive, with maximum activity registered at 60°C. The NADP(H) dependent enzyme was haloalkaliphilic for the oxidative reaction with optimum activity at pH 10.0. It favored a slightly acidic pH of 6.0 for catalysis of the reductive reaction. HmADH12 was significantly more tolerant than mesophilic ADHs to selected organic solvents, making it a much more suitable biocatalyst for industrial application.
      755Scopus© Citations 26
  • Publication
    One-step diketopiperazine synthesis using phase transfer catalysis
    A simple and efficient one-step procedure is described for the synthesis of a number of symmetrical 1,4-disubstituted piperazine-2,5-diones under phase transfer conditions. The reactions are carried out at room temperature, starting from a suitable N-chloroacetamide in the presence of an aqueous solution of sodium hydroxide. Piperazine-2,5-diones were obtained with excellent selectivity in yields of up to 90%.
      458Scopus© Citations 22
  • Publication
    From amines to diketopiperazines: a one-pot approach
    An efficient one-pot synthesis is described for the preparation of 1,4-disubstituted piperazine-2,5-diones starting from a suitable amine and chloroacetyl chloride in the presence of an aqueous base. The resulting chloroacetamide is cyclised in situ by employing the phase-transfer (PT) catalyst, benzyltriethylammonium chloride (TEBA). The products are isolated in excellent yields of up to 90%.
      315Scopus© Citations 5
  • Publication
    Effect of organic solvents on the activity and stability of halophilic alcohol dehydrogenase (ADH2) from Haloferax volcanii
    (Springer, 2013-01-01) ;
    The effect of various organic solvents on the catalytic activity, stability and substrate specificity of alchohol dehydrogenase from Haloferax volcanii (HvADH2) was evaluated. The HvADH2 showed remarkable stability and catalysed the reaction in aqueous–organic medium containing dimethyl sulfoxide (DMSO) and methanol (MeOH). Tetrahydrofuran and acetonitrile were also investigated and adversely affected the stability of the enzyme. High concentration of salt, essential to maintain the enzymatic activity and structural integrity of the halophilic enzyme under standard conditions may be partially replaced by DMSO and MeOH. The presence of organic solvents did not induce gross changes in substrate specificity. DMSO offered a protective effect for the stability of the enzyme at nonoptimal pHs such as 6 and 10. Salt and solvent effects on the HvADH2 conformation and folding were examined through fluorescence spectroscopy. The fluorescence findings were consistent with the activity and stability results and corroborated the denaturing properties of some solvents. The intrinsic tolerance of this enzyme to organic solvent makes it highly attractive to industry.
      293Scopus© Citations 34
  • Publication
    A simple and efficient method for the synthesis of Erlenmeyer azlactones
    We have recently developed a novel and efficient method for synthesising Erlenmeyer azlactones under mild and rapid conditions. The reaction is performed by reacting 2-phenyl-5-oxazolone with an aldehyde in dichloromethane using alumina as a catalyst. The materials react instantly at room temperature, negating the need for high temperatures and long reaction times. We have successfully used this method for both aliphatic, aromatic and heteroaromatic aldehydes, synthesising previously unmade Erlenmeyer azlactones in moderate to high yields.
      2607Scopus© Citations 60
  • Publication
    His-tagged Horse Liver Alcohol Dehydrogenase: Immobilization and application in the bio-based enantioselective synthesis of (S)-arylpropanols
    The novel histidine-tagged Horse Liver Alcohol Dehydrogenase (His-HLADH-EE) was successfully purified and covalently immobilized onto a solid support in a one-step procedure through a metal-directed technique. A full characterization of the immobilized enzyme was carried out. Effects of pH, temperature and organic co-solvents were deeply investigated and they showed a shift in the optimum pH with respect to the free form as well as increased stability to temperature and solvents. The immobilized His-HLADH-EE proved to be effective as catalyst in the reduction of aliphatic and aromatic aldehydes. Application of the free and immobilized His-HLADH-EE to the chemo-enzymatic synthesis of (S)-Profenols demonstrated enhanced enantioselectivity and high reusability of the immobilized form. The achievement of a robust and effective immobilization of an alcohol dehydrogenase substantiated the use of biocatalytic reduction in the synthesis of primary alcohols and valuable chiral intermediates especially for pharmaceutical industries.
      449Scopus© Citations 33