Highly efficient coenzyme regeneration system for reduction of cyclohexanone by horse liver alcohol dehydrogenase in organic solvent

Summary The coenzyme NADH was efficiently regenerated from NAD by 3-pentanol or cyclooctanol for reduction of cyclohexanone by the catalysis of HLADH in an aqueous-organic two-phase reaction system.     

Efficient Repeated Use of Alcohol Dehydrogenase with NAD + Regeneration in an Aqueous-organic Two-phase System

Bioconversion of cinnamyl alcohol to cinnamaldehyde was carried out in an aqueous-organic two-phase reaction system by the repeated use of horse liver alcohol dehydrogenase (HLADH) and NAD + with coenzyme regeneration. Both HLADH and the coenzyme were efficiently entrapped in the aqueous phase, while the substrate was supplied successively from the organic phase and the product was accumulated in the organic phase. Optimum conditions for cinnamaldehyde production in the aqueous-organic two-phase system were also examined, including substrate concentration, pH, and organic solvent type. Under suitable conditions, both HLADH and NAD + in the aqueous-organic two-phase system could be reused, and NAD + cycling numbers of 3040 were obtained after repeated operation for 40 &#117 h.     

Efficient Repeated Use of Alcohol Dehydrogenase with NAD + Regeneration in an Aqueous-organic Two-phase System

Bioconversion of cinnamyl alcohol to cinnamaldehyde was carried out in an aqueous-organic two-phase reaction system by the repeated use of horse liver alcohol dehydrogenase (HLADH) and NAD + with coenzyme regeneration. Both HLADH and the coenzyme were efficiently entrapped in the aqueous phase, while the substrate was supplied successively from the organic phase and the product was accumulated in the organic phase. Optimum conditions for cinnamaldehyde production in the aqueous-organic two-phase system were also examined, including substrate concentration, pH, and organic solvent type. Under suitable conditions, both HLADH and NAD + in the aqueous-organic two-phase system could be reused, and NAD + cycling numbers of 3040 were obtained after repeated operation for 40 λh.     

Monitoring of occupational exposure to cyclohexanone by diffusive sampling and urinalysis

The present study was initiated in order to identify the best marker of occupational exposure to cyclohexanone among cyclohexanone and its metabolites in urine. To examine if diffusive samplers are applicable to personal monitoring of exposure to cyclohexanone in workroom air, the performance of carbon cloth to adsorb cyclohexanone in air was studied by experimental exposure of the cloth to cyclohexanone at 5, 10, 25 or 50 ppm (i.e. 20, 40, 100 or 200 mg m-3) for up to 8 h. Cyclohexanone in the exposed cloth was extracted with carbon disulphide followed by gas chromatographic (GC) analysis. The cloth adsorbed cyclohexanone in proportion to the concentration (up to 50 ppm) and the duration (up to 8 h), and responded quantitatively to a 15 min exposure at 100 ppm. In a field survey, end-of-shift urine samples were collected from 24 factory workers occupationally exposed to cyclohexanone (up to 9 ppm) in combination with toluene and other solvents. Urine samples were also collected from 10 subjects with no occupational exposure to solvents. The urine samples were treated with acid or an enzyme preparation for hydrolysis, and extracted with dichloromethane or ethyl acetate. The extracts were analysed by GC for cyclohexanone, cyclohexanol, and trans- and cis-isomers of 1,2- and 1,4-cyclohexanediol. Both cyclohexanol and trans-1,2-cyclohexanediol in urine correlated significantly with time-weighted average intensity of exposure to cyclohexanone. Although trans -1,4-isomer was also excreted, its quantitative relation with cyclohexanone exposure could not be established, because the solvent extraction rate was low and unstable. Excretion of cis-isomers was not confirmed. The two analytes, cyclohexanol and trans-1,2-cyclohexanediol, appeared to be equally valid as exposure markers, but the latter may be superior to the former in the sense that it is sensitive enough to separate the exposed from the non-exposed at 1 ppm or less cyclohexanone exposure.     

Monitoring of occupational exposure to cyclohexanone by diffusive sampling and urinalysis

The present study was initiated in order to identify the best marker of occupational exposure to cyclohexanone among cyclohexanone and its metabolites in urine. To examine if diffusive samplers are applicable to personal monitoring of exposure to cyclohexanone in workroom air, the performance of carbon cloth to adsorb cyclohexanone in air was studied by experimental exposure of the cloth to cyclohexanone at 5, 10, 25 or 50 ppm (i.e. 20, 40, 100 or 200 mg m-3) for up to 8 h. Cyclohexanone in the exposed cloth was extracted with carbon disulphide followed by gas chromatographic (GC) analysis. The cloth adsorbed cyclohexanone in proportion to the concentration (up to 50 ppm) and the duration (up to 8 h), and responded quantitatively to a 15 min exposure at 100 ppm. In a field survey, end-of-shift urine samples were collected from 24 factory workers occupationally exposed to cyclohexanone (up to 9 ppm) in combination with toluene and other solvents. Urine samples were also collected from 10 subjects with no occupational exposure to solvents. The urine samples were treated with acid or an enzyme preparation for hydrolysis, and extracted with dichloromethane or ethyl acetate. The extracts were analysed by GC for cyclohexanone, cyclohexanol, and trans- and cis-isomers of 1,2- and 1,4-cyclohexanediol. Both cyclohexanol and trans-1,2-cyclohexanediol in urine correlated significantly with time-weighted average intensity of exposure to cyclohexanone. Although trans -1,4-isomer was also excreted, its quantitative relation with cyclohexanone exposure could not be established, because the solvent extraction rate was low and unstable. Excretion of cis-isomers was not confirmed. The two analytes, cyclohexanol and trans-1,2-cyclohexanediol, appeared to be equally valid as exposure markers, but the latter may be superior to the former in the sense that it is sensitive enough to separate the exposed from the non-exposed at 1 ppm or less cyclohexanone exposure.     

Kinetic resolution of organosilicon compounds by stereoselective dehydrogenation with horse liver alcohol dehydrogenase

Streoselective dehydrogenation of three isomers of trimethylsilypropanol was carried out with horse liver alcohol dehydrogenase (HLADH, EC 1.1.1.1.) and optically active organosilicon compounds were obtained in a water-organic solvent two-layer system with coenzyme regeneration. Furthermore, we examined the effects of the silicon atom on stereoselectivity of HLADH compared to the corresponding carbon compounds. Substitution of the silicon atom for the carbon atom was found to improve the stereoselectivity of HLADH. For example, the optical purity of the remaining 1-trimethylsilyl-2-propanol was higher than 99% enantiomeric excess (ee) at 50% conversion, whereas that of the carbon analogue was 84% ee. This phenomenon was probably ascribable to the bulkiness of the organosilicon compounds derived from their longer Si-C bond. Kinetic analysis in an aqueous monolayer system demonstrated that the specific properties of the silicon atom greatly affected the reactivity of these substrate compounds.Correspondence to: A. Tanaka     

Membrane electrochemical reactors (MER) for NADH regeneration in HLADH-catalysed synthesis: comparison of effectiveness

Two membrane electrochemical reactors (MER) were designed and applied to HLADH-catalysed reduction of cyclohexanone to cyclohexanol. The regeneration of the cofactor NADH was ensured electrochemically, using either methyl viologen or a rhodium complex as electrochemical mediator. A semi-permeable membrane (dialysis or ultra-filtration) was integrated in the filter-press electrochemical reactor to confine the enzyme(s) as close as possible to the electrode surface. When methyl viologen was used, the transformation ratio of cyclohexanone varied from 0 to 65% depending on the internal arrangement of the reactor. Matching the reactor configuration to the reaction system was essential in this case. With the rhodium complex, the ultra-filtration MER was tested in continuous and recycling configurations. The best conditions led to 100% transformation of 0.1 L volume of 0.1 M cyclohexanone after 70 h with the recycling mode. Finally, the performances of the reactors are discussed with respect to different evaluations of the production yields.     

Hydrolysis and reduction of factor 390 by cell extracts of Methanobacterium thermoautotrophicum (strain delta H).

Cell extracts of Methanobacterium thermoautotrophicum (strain delta H) were found to perform a hydrogen-dependent reduction of factor 390 (F390), the 8-adenylyl derivative of coenzyme F420. Upon resolution of cell extracts, F390-reducing activity copurified with the coenzyme F420-dependent hydrogenase. This indicates that F390 serves as a substrate of that enzyme. Activity towards F390 was approximately 40-fold lower than that towards coenzyme F420 (0.12 and 5.2 mumol.min-1.mg of protein-1, respectively). In addition, cell extracts catalyzed the hydrolysis of F390 to AMP and coenzyme F420. This hydrolysis required the presence of thiols (6 mM) and much ionic strength (1 M KCl) and was reversibly inhibited by oxygen. The reaction proceeded optimally at pH 8.2 and was Mn dependent. Conditions for F390 hydrolysis in cell extracts are in many respects opposite to those previously described for F390 synthesis.     

Purification and catalytic properties of Ech hydrogenase from Methanosarcina barkeri.

Methanosarcina barkeri has recently been shown to produce a multisubunit membrane-bound [NiFe] hydrogenase designated Ech (Escherichia coli hydrogenase 3) hydrogenase. In the present study Ech hydrogenase was purified to apparent homogeneity in a high yield. The enzyme preparation obtained only contained the six polypeptides which had previously been shown to be encoded by the ech operon. The purified enzyme was found to contain 0.9 mol of Ni, 11.3 mol of nonheme-iron and 10.8 mol of acid-labile sulfur per mol of enzyme. Using the purified enzyme the kinetic parameters were determined. The enzyme catalyzed the H2 dependent reduction of a M. barkeri 2[4Fe-4S] ferredoxin with a specific activity of 50 U x mg protein-1 at pH 7.0 and exhibited an apparent Km for the ferredoxin of 1 microM. The enzyme also catalyzed hydrogen formation with the reduced ferredoxin as electron donor at a rate of 90 U x mg protein-1 at pH 7.0. The apparent Km for the reduced ferredoxin was 7.5 microM. Reduction or oxidation of the ferredoxin proceeded at similar rates as the reduction or oxidation of oxidized or reduced methylviologen, respectively. The apparent Km for H2 was 5 microM. The kinetic data strongly indicate that the ferredoxin is the physiological electron donor or acceptor of Ech hydrogenase. Ech hydrogenase amounts to about 3% of the total cell protein in acetate-grown, methanol-grown or H2/CO2-grown cells of M. barkeri, as calculated from quantitative Western blot experiments. The function of Ech hydrogenase is ascribed to ferredoxin-linked H2 production coupled to the oxidation of the carbonyl-group of acetyl-CoA to CO2 during growth on acetate, and to ferredoxin-linked H2 uptake coupled to the reduction of CO2 to the redox state of CO during growth on H2/CO2 or methanol.     

Cyclohexanone monooxygenase catalyzed oxidation of methyl phenyl sulfide and cyclohexanone with macromolecular NADP in a membrane reactor

Summary Methyl phenyl sulfide and cyclohexanone were oxidized to (R)- methyl phenyl sulfoxide and caprolactone by cyclohexanone monooxygenase. The reactions were carried out in a membrane reactor with the use of the macromolecular coenzyme poly (ethylene glycol)-NADP. Coenzyme regeneration was carried out with the 2-propanol/alcohol dehydrogenase system.     

一株太平洋深海环己酮降解菌的筛选与功能研究

从太平洋深海菌株中筛选到一株能以环己酮为唯一碳源生长的微球菌(CN1),其最适生长温度为25℃~37℃,最适生长pH8,最适生长盐度6%。该菌可耐受高浓度环己酮(>44% V/V),并且在16.7%(V/V)的环己酮中生长最好。CN1可转化环己醇成环己酮,环己酮又可被快速降解、矿化。这表明该菌含有环己醇脱氢酶并且很可能还含有环己酮单加氧酶。通过兼并PCR克隆到450bp环己酮单加氧酶基因片段,其编码的氨基酸序列不仅具有Baeyer-Villiger单加氧酶家族的保守序列,而且与节杆菌(Arthrobacter BP2)的环己酮单加氧酶同源性最高(80%),而与研究较深入的不动杆菌(Acinetobacter sp.NCIMB 9871)单加氧酶的同源性仅为53%。由于目前报道的环己醇和环己酮的降解都是通过环己酮单加氧酶进行的,所以CN1的环己酮单加氧酶应该负责环己酮的降解。目前报道的环己酮降解菌都可以降解环戊酮,而CN1不可降解环戊酮,暗示了CN1的环己酮单加氧酶比较特别。另外,我们还首次发现在CN1中环己醇对环己酮的降解有一定的抑制作用。     

The metabolism of cyclohexanol by Nocardia globerula CL1

1. Nocardia globerula CL1, isolated by enrichment on cyclohexanol and grown with it as carbon source, oxidized it with a Q(o2) of 39mul/h per mg dry wt. and the overall consumption of 2.2mumol of oxygen/mol of substrate. Cyclohexanone, 2-hydroxycyclohexan-1-one dimer and cyclohexane-1,2-dione were oxidized with Q(o2) values similar to that for cyclohexanol whereas in-caprolactone and 6-hydroxycaproate were oxidized very slowly and adipate not all. 2. Disrupted cell suspensions could not be shown to catalyse the conversion of cyclohexanol into cyclohexanone. 3. A cyclohexanol-induced cyclohexanone oxygenase (specific activity 0.55mumol of NADPH oxidized/min per mg of protein) catalysed the consumption of 1mol of NADPH and 1mol of O(2) in the presence of 1mol of cyclohexanone. NADPH oxidation did not occur under anaerobic conditions. The only detected reaction product with 25000g supernatant was 6-hydroxycaproate. 4. Extracts of cyclohexanol-grown cells contained a lactone hydrolase (specific activity 15.6mumol hydrolysed/min per mg of protein), which converted in-caprolactone into 6-hydroxycaproate. 5. Incubation of 6-hydroxycaproate with 25000g supernatant in the presence of NAD(+) resulted in NAD(+) reduction under anaerobic conditions, oxygen consumption under aerobic conditions and the conversion of 6-hydroxycaproate into adipate. 6. Cyclohexanone oxygenase fractions devoid of in-caprolactone hydrolase catalysed the stoicheiometric formation of in-caprolactone from cyclohexanone in the presence of excess of NADPH. 7. The reaction sequence for the oxidation of cyclohexanone by N. globerula CL1 is: cyclohexanol --> cyclohexanone --> in-caprolactone --> 6-hydroxycaproate --> adipate. 8. It is suggested that the adipate may be further dissimilated by beta-oxidation.     

Protein-coated Microcrystals for use in Organic Solvents: Application to Oxidoreductases

Protein-coated microcrystals (PCMC), a biocatalyst preparation previously demonstrated to display substantially increased transesterification activity of proteases and lipases in organic solvents when compared to their as received counterparts [Kreiner M, Moore BD, Parker MC (2001) Chem. Commun. 12:1096--1097], was applied to oxidoreductases. Horse liver alcohol dehydrogenase (HLADH), catalase (CAT), soybean peroxidase and horseradish peroxidase were immobilised onto K₂SO₄ crystals and dehydrated in a 1-step process, resulting in PCMC. These PCMC preparations showed enhanced activity in different organic solvents in most types of reactions tested. The highest activation was observed with HLADH (50-fold as active as enzyme as received) and CAT (25-fold).     

FAD requirement for the reduction of coenzyme F420 by hydrogenase from Methanobacterium formicicum

Hydrophobic interaction chromatography of coenzyme F420-reducing hydrogenase purified from Methanobacterium formicicum depleted protein-bound FAD and eliminated the ability to reduce coenzyme F420. Preincubation of the FAD-depleted hydrogenase with FAD restored 85% of the coenzyme F420-reducing activity. FMN did not replace FAD. A Kd of 12 microM was estimated for FAD. Analysis of the reactivated hydrogenase following molecular sieve column chromatography showed that FAD was bound to protein. The results indicate that protein-bound FAD is reversibly removed from the coenzyme F420-reducing hydrogenase and that this flavin is required for the reduction of coenzyme F420.     

Optimization of Peroxidase-Catalyzed Oxidation of Luminol in Reversed Micelles of Surfactants in Octane

Luminol oxidation in the Aerosol OT (AOT) reversed micelles in octane catalyzed by horseradish peroxidase (HRP), or its conjugate with Cortisol (HRP-COR), was optimized. The chemiluminescence intensity during luminol oxidation was strongly dependent on the method of preparation of the reaction mixture and the addition of Triton X-45, cyclohexanol and the chemiluminescence “enhancer”, p-iodophenol, into the micellar system. Five procedures for the preparation of the reaction mixture were compared. The maximum chemiluminescence was observed in the micellar system containing all the reaction components excluding a biocatalyst, addition of which into the system started the reaction. Triton X-45, cyclohexanol or p-iodophenol added to the micellar system enhanced significantly the chemiluminescence intensity. The “enhancing” action of p-iodophenol in AOT reversed micelles was 10-fold less than in an aqueous medium.     

Co-expression of P450 BM3 and glucose dehydrogenase by recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis> and its application in an NADPH-dependent indigo production system

P450 BM3 mutant can catalyze indole to indoxyl, and indoxyl can dimerize to form indigo. But the reaction catalyzed by P450 BM3 requires NADPH, as coenzyme regeneration is very important in this system. As we know, when glucose dehydrogenase oxidizes glucose to glucolactone, NADH or NADPH can be formed, which can contribute to NADPH regeneration in the reaction catalyzed by P450 BM3. In this paper, a recombinant Escherichia coli BL21 (pET28a (+)-P450 BM3-gdh0310) was constructed to co-express both P450 BM3 gene and glucose dehydrogenase (GDH) gene. To improve the expression level of P450 BM3 and GDH in E. coli and to avoid the complex and low-efficiency refolding operation in the purification procedure, the expression conditions were optimized. Under the optimized conditions, the maximum P450 BM3 and GDH activities amounted to 8173.13 and 0.045 U/mg protein, respectively. Then bioconversion of indole to indigo was carried out by adding indole and glucose to the culture after improved expression level was obtained under optimized conditions, and 2.9 mM (760.6 mg/L) indigo was formed with an initial indole concentration of 5 mM.     

Purification and properties of the membrane-associated coenzyme F420-reducing hydrogenase from Methanobacterium formicicum.

The membrane-associated coenzyme F420-reducing hydrogenase of Methanobacterium formicicum was purified 87-fold to electrophoretic homogeneity. The enzyme contained alpha, beta, and gamma subunits (molecular weights of 43,000, 36,700, and 28,800, respectively) and formed aggregates (molecular weight, 1,020,000) of a coenzyme F420-active alpha 1 beta 1 gamma 1 trimer (molecular weight, 109,000). The hydrogenase contained 1 mol of flavin adenine dinucleotide (FAD), 1 mol of nickel, 12 to 14 mol of iron, and 11 mol of acid-labile sulfide per mol of the 109,000-molecular-weight species, but no selenium. The isoelectric point was 5.6. The amino acid sequence I-N3-P-N2-R-N1-EGH-N6-V (where N is any amino acid) was conserved in the N-termini of the alpha subunits of the F420-hydrogenases from M. formicicum and Methanobacterium thermoautotrophicum and of the largest subunits of nickel-containing hydrogenases from Desulfovibrio baculatus, Desulfovibrio gigas, and Rhodobacter capsulatus. The purified F420-hydrogenase required reductive reactivation before assay. FAD dissociated from the enzyme during reactivation unless potassium salts were present, yielding deflavoenzyme that was unable to reduce coenzyme F420. Maximal coenzyme F420-reducing activity was obtained at 55 degrees C and pH 7.0 to 7.5, and with 0.2 to 0.8 M KCl in the reaction mixture. The enzyme catalyzed H2 production at a rate threefold lower than that for H2 uptake and reduced coenzyme F420, methyl viologen, flavins, and 7,8-didemethyl-8-hydroxy-5-deazariboflavin. Specific antiserum inhibited the coenzyme F420-dependent but not the methyl viologen-dependent activity of the purified enzyme.     

Synthesis and properties of new coenzyme mimics based on the artificial coenzyme CL4

We have previously shown that a range of nicotinamide containing ‘biomimetic coenzymes’ function as active analogues of NAD⁺ in the oxidation of alcohols by horse liver alcohol dehydrogenase (HLADH), despite their apparently astonishing lack of structural similarity to the natural coenzyme. The simplest structure as yet shown to exhibit activity is the biomimetic coenzyme CL4. To investigate the effect of the structure of this truncated artificial coenzyme on its activity, a range of close structural analogues of CL4 were designed, synthesized and characterized. The electrochemical reduction potentials of the analogues were strongly influenced by the nature of the groups attached to the pyridine ring. All of the analogues could be chemically reduced using sodium borohydride, to give compounds with altered UV‐visible absorption and fluorescence properties. An HPLC‐based assay suggested that two of the new analogues were coenzymically active in the oxidation of butan‐1‐ol by HLADH, with one displaying a significantly higher activity than CL4. The results demonstrate which features of the structures of the coenzymes lead to desirable electrochemical and spectroscopic properties, but suggest that the structural requirements for a functional coenzyme are quite stringent. These observations may be used to design an artificial coenzyme which combines the best features of those studied so far. Copyright Copyright © 1999 John Wiley & Sons, Ltd.     

Analysis of the inactivation of liver alcohol dehydrogenase during storage in Aerosol-OT/isooctane microemulsions

Changes in the enzymatic properties of horse liver alcohol dehydrogenase (HLADH; EC 1.1.1.1) were studied as a function of incubation time in Aerosol-OT/isooctane microemulsions. The enzyme was characterized by fluorimetric binding studies of the inhibitor isobutyramide to the binary complex, HLADH-NADH and by determination of Km,app and Vmax,app values for cyclohexanone. The Km,app values for cyclohexanone and the Kd,app for isobutyramide stay constant throughout a 48-h incubation, whereas the Vmax,app and the total number of inhibitor binding sites decrease. Thus the inactivation process previously described corresponds to progressive loss of functional sites, while the properties of the remaining functional sites are unchanged. If no co-enzyme is added to the system, the enzyme loses catalytic activity within less than an hour, but if co-enzyme is added, a fraction of the HLADH enzyme population retains enzyme activity over a long period of time. Hence the presence of bound co-enzyme significantly inhibits the process(es) leading to inactivation of the enzyme in the microemulsions.     

Substrate activation and inhibition in coenzyme–substrate reactions. Cyclohexanol oxidation catalysed by liver alcohol dehydrogenase

1. The activity of liver alcohol dehydrogenase with cyclohexanol and cyclohexanone as substrates was studied, and the initial-rate parameters were determined from measurements at low substrate concentrations. In contrast with aliphatic ketones, cyclohexanone is a fairly good substrate, although less active than aliphatic aldehydes. The Michaelis constant for cyclohexanol is of the same order as that for ethanol, and the maximum rate and Michaelis constant for NAD(+) obtained with cyclohexanol are very similar to those obtained with primary aliphatic alcohols. The data for this substrate at low concentrations are therefore consistent with a compulsory-order mechanism in which ternary complexes are not rate-limiting. 2. With large concentrations of NAD(+), substrate activation is observed with increasing concentrations of cyclohexanol, whereas with small NAD(+) concentrations substrate inhibition is observed. This complex behaviour is explained by a mechanism previously proposed for this enzyme, which also satisfactorily described the kinetics of oxidation of primary and secondary aliphatic alcohols and aldehydes, including the substrate inhibition exhibited by primary alcohols, and the reduction of aldehydes. The activation with large concentrations of both NAD(+) and cyclohexanol is attributed to the formation of an abortive complex, E.NADH.ROH, from which NADH dissociates more rapidly than from the normal product complex E.NADH. Substrate inhibition in the presence of small NAD(+) concentrations is attributed to the formation of an active complex E.ROH, with which NAD(+) reacts more slowly than with the free enzyme. 3. Some support for these mechanisms of substrate activation and inhibition is obtained by approximate theoretical calculations, and their applicability to other two-substrate reactions that exhibit complex initial-rate behaviour, as a more likely alternative to the postulate of a second binding site for the substrate, is suggested.