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• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M21/00—Bioreactors or fermenters specially adapted for specific uses
  • C12M21/18—Apparatus specially designed for the use of free, immobilized or carrier-bound enzymes
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M35/00—Means for application of stress for stimulating the growth of microorganisms or the generation of fermentation or metabolic products; Means for electroporation or cell fusion
  • C12M35/08—Chemical, biochemical or biological means, e.g. plasma jet, co-culture
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P1/00—Preparation of compounds or compositions, not provided for in groups C12P3/00 - C12P39/00, by using microorganisms or enzymes
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/24—Preparation of oxygen-containing organic compounds containing a carbonyl group

Definitions

• This invention relates to enzymatic processes, in particular to processes for the oxidative or reductive transformation of organic compounds utilising redox enzymes.
• Redox enzymes such as external mono-oxygenases catalyse a wide range of oxidation and reduction reactions in biological systems, many of which are potentially of great industrial importance. In order to accomplish their enzymatic functions, however, these enzymes require a continuing supply of reducing equivalents, normally in the form of electrons, which, in biological systems, are supplied to the enzyme by biologically active electron donor materials, such as NAD and cytochromes. In nature these donor materials undergo continuous regeneration in interactions associated with the main enzyme reaction, but industrial applications of these enzymes would not normally permit this regeneration to take place and thus a continuing supply of fresh donor material would be required to drive the enzyme reaction.
• electrochemical regeneration of NAD in enzymatically active form has been investigated with a view to coupling this regeneration with enzymatic reactions in which NAD interacts with a substrate material.
• electrochemical regeneration of the oxidised form of NAD has been coupled with alcohol dehydrogenation catalysed by alcohol dehydrogenase immobilised on alumina (Coughlin et al Biotechnology and Bioengineering (1975) Vol. XVII, pages 515-526) in a reaction in which free NAD + is electrochemically regenerated and acts as a hydrogen acceptor converting the alcohol to an aldehyde.
• the alcohol dehydrogenase of this reaction acts as a site for interaction of the NAD + and the alcohol, and does not itself undergo chemical change during the reaction to provide an enzymically active reduced enzyme species.
• Electron donor materials such as NAD and cytochromes are highly costly, complex, unstable chemicals, some comprising protein components and thus their use as reagents in industrial processes is not at present practical.
• the present invention comprises a process for carrying out an enzymatic reaction which requires a continuing supply of reducing equivalents to regenerate a reduced enzyme species in enzymatically active form, in which the reducing equivalents are derived electrochemically.
• Suitable enzymes are characteristically those which are capable of accepting electrons to produce a reduced enzyme species which generally corresponds to the enzymatically active form of the enzyme.
• the enzymes typically comprise at least one electron receptor component which is an integral part of the enzyme molecule or system.
• theenzyme may comprise a single identifiable molecular species which contains either a metal atom which is directly reduced, or a small molecular prosthetic group permanently bound to the enzyme, such as a flavo protein or pteridine, or a normally free species e.g. NAD, which is bound by the enzyme and whilst bound is reduced and acts as the electron receptor.
• the enzyme may comprise a multi-protein complex, in which case there is at least one species within the complex, such as ferredoxin, rubredoxin or a cytochrome e.g. cytochrome P450, which acts as an electron receptor and supplies the reducing electrons to the reactive species in the enzyme complex, often by way of a chain of intermediate proteins.
• a species within the complex such as ferredoxin, rubredoxin or a cytochrome e.g. cytochrome P450, which acts as an electron receptor and supplies the reducing electrons to the reactive species in the enzyme complex, often by way of a chain of intermediate proteins.
• the enzymes which may be used in the process of the present invention are typically redox enzymes including external mono-oxygenases, oxidoreductases, dehydrogenases, hydrogenases, nitrogenases, dioxygenases and luciferases.
• redox enzymes including external mono-oxygenases, oxidoreductases, dehydrogenases, hydrogenases, nitrogenases, dioxygenases and luciferases.
• the enzymatic reactions of the invention are those which involve incorporation of molecular oxygen to provide an enzyme/substrate/molecular oxygen complex during reaction.
• suitable enzymes and enzymatic reactions utilising these enzymes will be apparent to workers skilled in the art.
• the processes of the invention are processes for the oxidative or reductive transformation of organic compounds in which the transformation is catalysed by an enzyme and the enzyme requires a continuing supply of reducing equivalents to regenerate a reduced enzyme species in enzymatically active form, and in which the reducing equivalents are derived electrochemically.
• the organic compounds which may be transformed by the processes of the invention are compounds which characteristically comprise hydrocarbon material and may also comprise functional groups, such as hydroxyl, carbonyl and other groups, and the transformations which may be carried out may be transfor mations of the hydrocarbon material and/or functional groups attached thereto. It will be appreciated that many of such transformations are potentially of great industrial importance.
• enzymes and enzymatic processes for effecting transformation of organic compounds to which the present invention may be applied include: 1. External Mono-Oxygenases -
• Microbial higher alkane mono-oxygenases of both of cytochrome P-450 and rubredoxin classes including oxygenases of alkanes e.g. n-octane, alicyclic hydrocarbons, and related systems especially terpenes.
• Microbial flavin mono-oxygenases such as p-hydroxy- benzoate, salicylate, orcinol and melilotate mono- oxygenases.
• NADH-linked methane mono-oxygenases for instance the systems isolated from Methylococcus capsulatus or Methylosinus trichosporium which show a very broad substrate specificity, e.g. as described by Higgins et al, Society of General Microbiology Quarterly, 6, 71 (1979) and Biochemical Biophysical Research Communications (1979) (in press), and by
• Oxidoreductases e.g. ethanol, methanol, lactate, fumarate, succinate oxidoreductases (i.e. including NAD-, flavin- and pteridine-linked enzymes).
• Dehydrogenases e.g. pyruvate and 2-oxo-glutarate dehydrogenases. 4. Nitrogenase.
• Dioxygenases that require a reducing agent e.g. bacterial benzene and toluene oxygenases.
• the electrochemically derived reducing equivalents i.e. electrons may be passed indirectly to the enzyme by means of a suitable carrier.
• the carrier may comprise a naturally occurring biological carrier such as those biologically active electron donor materials e.g. ferredoxin, pteridine, NAD(P)H, flavins, rubredoxin or free cytochromes, which are associated with the function of enzymes in biological systems.
• the carrier may comprise an artificial carrier, such as quinone, viologen dye, glutathione or ascorbic acid.
• the electrochemically derived reducing equivalents are passed directly to the enzyme from the cathode of the electro-chemical system and are used and taken up by the electron receptor component e.g.
• the choice of electrodes and electrochemical cell used as well as careful control of the electrochemical conditions employed have been found to be of importance.
• material which is inert to the biologically active material which it is desired to reduce electrochemically is generally used for the working electrode e.g. gold, platinum, carbon or mercury, and the auxiliary electrode, which may be any suitable material, e.g. graphite, is separated from the working electrode, for instance by an electrically conducting membrane.
• the electro-chemical conditions employed it is of primary importance to ensure that electron transfer to the carrier or enzyme is not rendered ineffective e.g. by the carrier or enzyme undergoing chemical change, or decomposition or by becoming absorbed at the working electrode i.e.
• cathode This may be achieved by use of a liquid crystal coated, serai-conductor or hanging mercury drop working electrode and/or by use of an electron transfer promoter in the electrolyte.
• Suitable promoters include 4, 4' -bipyridyl, and 1, 2 - (bis-4,4'-bipyridyl) ethylene and similar conjugated and/or heterocyclic chemicals.
• the potential of the working electrode at or close to the redox potential of the enzyme or carrier species which it is desired to reduce electrochemically.
• Such control of the potential of the working electrode advantageously permits se. active reduction of the desired enzyme or carrier species, fcr instance, even when the desired enzyme is present in a complex mixture, such as a crude cell extract.
• the redox potentials of each enzyme or carrier species are typically distinctive of the species.
• the redox potential of the mono-cxygenase enzyme system of Methylosinus trichosporium has been found to be approximately -0.1v versus the potential of the normal hydrogen electrode.
• the desired redox potentials may be determined empirically in each case by methods well known in the electrochemical art.
• a third electrode is typically included within the electrochemical cell.
• a reference electrode such as a standard calomel reference electrode, is used, preferably located within the working region of the cell especially in close proximity to the working electrode. Any suitable means may be used to control the potential of the working electrode, such as, for example a potentiostat.
• the enzyme is introduced into the working compartment of a suitable electrochemical cell, electrochemically derived reducing equivalents are supplied to the enzyme, and substrate is supplied to the system and products recovered as desired.
• regeneration of the enzyme and transformation of the organic compound substrate material takes place simul taneously, for instance in a homogeneous system.
• the enzyme may be in purified form, although this is not normally necessary as choice of preferred operating potential advantageously permits selective electrochemical regeneration of the enzyme e.g. as a component of a crude cell extract.
• the enzyme may be present in the electrolyte in the free state, or, in preferred embodiments for use in industrial applications, the enzyme may be immobilised, for instance, on or with a suitable solid phase material e.g. polysaccharide gel beads or absorbed on carbon particles. Also immobilised enzyme may be used advantageously in flow-through reactor systems, in which substrate may be flowed through the reactor and products recovered down stream of the reactor.
• the required reducing equivalents may be supplied electrochemically from molecular hydrogen.
• molecular hydrogen is passed into a secondary solution in which the reaction H 2 ⁇ 2H + + 2e occurs e.g. a solution containing a hydrogenase.
• This solution contains an electrode e.g. a platinised platinum electrode, which is electrically connected to a second electrode immersed in a primary solution containing the enzymatic reaction system.
• Electrons supplied by the reaction of molecular hydrogen in the secondary solution are passed to an enzyme in the primary solution enabling the enzyme to interact with substrate e.g. methane and molecular oxygen.
• the electrochemical/enzymatic oxidation of methane to methanol is carried out in an electrochemical cell using a crude enzyme extract of Methylosinus trichosporium.
• the electrochemical cell used consists of two compartments, a working compartment and an auxiliary compartment, separated from one another by a Vycor (Corning Inc.) glass membrane.
• the working compartment contains a gold foil working electrode of surface area approximately 9 cm 2 , and in close proximity a standard calomel reference electrode the tip of which is within 1 mm of the gold electrode.
• a graphite rod anode is situated in the auxiliary compartment, and both compartments contain potassium phosphate as electrolyte.
• the potential of the working electrode relative to the standard calomel electrode is controlled by a Princeton Applied Research potentiostat model 173.
• a crude cell-free extract of methane-grown Methylosinus trichosporium is prepared as described by Tonge, Harrison and Higgins (Biochemical Journal, 161, (1977), 333-344).
• 9.5 ml of the extract containing 85 mg. of protein is introduced to the working compartment of the electrochemical cell together with a few crystals of cupric chloride and 4,4'-bipyridyl (5mM).
• the potentiostat is set to maintain the potential of the working electrode relative to the standard calomel electrode at -0.1V vs. the normal hydrogen electrode.
• the contents of the electro-chemical cell are incubated at room temperature, and magnetically stirred, whilst methane/air mixture (1:1v/v) is bubbled through the working compartment.
• the electric current and gas flow are switched off and the contents of the working compartment are assayed for methanol produced from the methane.
• concentration of methanol in the mixture is found to be 60 ⁇ M. It was also found that the oxidation of methane to methanol was inhibited by carbon monoxide and cyanide, both of which are known inhibitors of the methane mono-oxygenase of Methylosinus trichosporium.
• the methane mono-oxygenase system of this organism is known to have a very broad substrate specificity, as described by
• Camphor is oxidised to 5-exo-hydroxy-camphor using the camphor mono-oxygenase complex of Pseudomonas putida, the reducing equivalents required to drive the reaction being supplied electrochemically directly to the enzyme.
• the enzyme complex which consists of cytochrome P 450 cam putidaredoxin and putidaredoxin reductase, is isolated from Pseudomonas putida strain PpG 786 using the procedures of Gunsalus and Wagner (Methods in Enzymology, 52, 166-188, 1978) except that bacterial disruption is modified by use of the lysozyme-EDTA method of O'Keefe et al (Methods in Enzymology, 52, 151-157, 1978).
• the reaction solution contained in the working compartment of the cell contains putidaredoxin (10 mg) , reductase (2 mg) and cytochrome P-450 (24 nanomoles) in 5-4 ml of Tris (0.05 M) , K Cl (0.1M) buffer at pH 7.4, and is saturated with camphor.
• the reaction is carried out at 28oC with a preferred applied potential of -800 mV vs S.C.E. No 5-exo-hydroxycamphor is detected at zero time but the concentration of this compound steadily increases with time, the presence of this product in the reaction mixture being determined by ether extraction of samples followed by analysis by gas liquid chromatography.
• the yield of hydroxy camphor obtained is of the order of 80 n mol/mg of protein/min.
• Luciferase a flavoprotein enzyme which catalyses the reaction NADH + FMN + aldehyde + O 2 ⁇ light + products, is investigated in a system in which the reducing equivalents required for the enzyme reaction are supplied electrochemically directly to the enzyme.
• the luciferase used is obtained from Vihrio Fisheri as supplied by Sigma Chemical Co., and identified as type II Cat. No. 2379.
• the luciferase reactions are carried out in an electrochemical cell sited adjacent to a photomultiplier tube of an Aminco photometer which is used to measure the light emitted during the reaction.
• the electrochemical cell used comprises two compartments, a working compartment containing the reaction mixture and a gold gauze working electrode, and an auxiliary compartment separated from the working compartment by dialysis tubing and containing a platinum wire counter electrode.
• the reaction mixture contains luciferase (7 mg), decyl aldehyde (0.05 ml) and phosphate buffer (1.5 ml at pH 7.0) being made up to a total volume of 8 ml.
• a standard calomel reference electrode is sited in the working compartment close to the working electrode and all three electrodes are appropriately connected to a Chemical Electronics potentiostat.
• the applied potential is arranged such that the working electrode is initially set at a potential of 0.0 V vs the S.C.E., after which the potential is gradually made more negative.
• the potential reaches -700 mV the photometer indicates that light is being emitted by the reaction mixture, and the amount of light emitted increases as the potential is made more negative.
• the most negative potential used being -900 mV. As the potential is made more positive the amount of light emitted decreases.
• the potential is cycled several times between 0V and -900 mV, and each time light is emitted at potentials more negative than 700 mV thereby showing that, the catalysis by the enzyme depended on the transfer of electrons from the electrode to the enzyme.
• the reducing equivalents are supplied electrochemically from molecular hydrogen in a heterogeneous system.
• the system used comprises two compartments separated by a glass frit membrane, one compartment containing a Johnson Matthey platinum fuel cell electrode (5 mm x 15 mm) maintained in phosphate buffer solution (pH 7) containing sodium perchlorate (0.01M).
• the other compartment of the system contains a gold net working electrode ( 10 mm x 5 mm) immersed in the same solution, though containing in addition cytochrome c (5 mg/ml) and 4,4-bipyridyl (10 mM) .
• the electrodes in the two compartments are provided with means for electrical connection between them, and the open circuit potential is found to be 630 mV, that which is expected from the reduction potential of cytochrome c.

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• 1979
  • 1979-08-10 WO PCT/GB1979/000139 patent/WO1980000453A1/en not_active Ceased
  • 1979-08-10 JP JP50123079A patent/JPS55500431A/ja active Pending
  • 1979-08-10 DE DE7979900897T patent/DE2966707D1/de not_active Expired
  • 1979-08-16 IT IT68676/79A patent/IT1165700B/it active
• 1980
  • 1980-03-25 EP EP79900897A patent/EP0020355B1/en not_active Expired
  • 1980-04-15 US US06/192,504 patent/US4318784A/en not_active Expired - Lifetime

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