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A potentiometric enzyme electrode is described for monitoring reactions in organic solvents. By use of an enzyme deposited on magnetic particles which are attracted to the tip of the electrode by means of a magnetic field, it is possible to produce an electrode in which the enzyme can easily be exchanged. As an example, studies of the chymotrypsin-catalyzed ester synthesis in diisopropyl ether and
The enzymatic oxidation of 1,2-cyclohexanediol and related substrates by Gluconobacter oxydans (ATCC 621) was investigated. At low pH, membrane-bound enzymes were active and at high pH, NAD-dependent, soluble enzymes showed activity. Whole bacterial cells were used to catalyze some bioconversions. Racemic trans-1,2-cyclohexanediol was oxidized at pH 3.5 to give (R)-2-hydroxycyclohexanone (96% e.e.
α‐Chymotrypsin was adsorbed on solid support materials and the catalytic activity of the preparations in organic solvents was studied. The activity was highly dependent on the nature of the support material and on the amount of water present in the reaction mixture. There appears to be competition for the water in the system between the enzyme, the support material and the solvent. The support mat
Protease‐catalyzed peptide synthesis in acetonitrile water mixtures, containing 0–90% water, was investigated. α‐Chymotrypsin, as well as thermolysin, were deposited on solid supports, prior to exposure to the reaction media. Peptide syntheses were performed using both a kinetically controlled process (chymotrypsin) and an equilibrium‐controlled synthesis (thermolysin). The activity of chymotrypsi
The enzyme mandelonitrile lyase was covalently immobilized on solid support materials using different methods. Immobilization on porous silica using coupling with glutaraldehyde afforded preparations with high enzyme loading (up to 9% (w/w)). The immobilized enzyme was used in a packed bed reactor for the continuous production of d-mandelonitrile from benzaldehyde and cyanide. The influence of the
The ability of several electron acceptors to promote the Gluconobacter oxydans catalyzed oxidation of glycerol was investigated. p-Benzoquinone was the most effective electron acceptor. The reaction rate obtained with p-benzoquinone was higher than the maximal rate with the natural electron acceptor, oxygen, in all the oxidation reactions tested.
Gas transport often is a limiting factor in biotechnology. Perfluorochemicals provide a new vehicle for the transport of gases.
Horse liver alcohol dehydrogenase (EC 1.1.1.1) solubilized in sodium dioctylsulfosuccinate (AOT)/cyclohexane reverse micelles was used for the oxidation of ethanol and reduction of cyclohexanone in a coupled substrate/coenzyme recycling system. The activity of the enzyme was studied as a function of pH and water content. The enzyme was optimally active in microemulsions prepared with buffer of pH
The influence of solvents on enzymatic activity and stability was investigated. As a model reaction the α-chymotrypsin-catalyzed esterification of N-acetyl-l-phenylalanine with ethanol was used. The enzyme was adsorbed on porous glass beads and used in various solvents. Small amounts of water were added to increase the enzymatic activity. These enzyme preparations obeyed. Michaelis-Menten kinetics
Coimmobilization of biocatalyst and substrate was studied as a method to increase the conversion rate in systems with substrates of extremely low solubility in water. The system studied was the conversion of hydrocortisone to prednisolone by Arthrobacter simplex. As a matrix for coimmobilization, alginate turned out to be superior to agar and agarose. After the reaction was complete, the beads wer
Theoretical calculations of reaction kinetics were done for one‐step reactions catalyzed by cells immobilized in spherical beads. The reactions catalyzed by free cells were assumed to obey Michaelis–Menten kinetics for a one‐substrate reaction. Both external (outside the beads) and internal (inside the beads) mass transfer of the substrate were considered for the immobilized preparations. The theo
Gluconobacter oxydans cells were immobilized in calcium alginate and the preparation was used for the oxidation of glycerol to dihydroxyacetone. The characterization was done according to the guidelines given by the Working Party on Immobilized Biocatalysts of the European Federation of Biotechnology. The pH optimum of the preparation was found to be 5.0 and the temperature optimum was 40°C. Howev
Oxygen supply is a critical point in technical processes when aerobic cells are used in immobilized preparations. In this study p-benzoquinone is used as a substitute for oxygen in the oxidation of glycerol to dihydroxyacetone by immobilized Gluconobacter oxydans cells. The reaction rate was much higher when p-benzoquinone was used compared to when oxygen was used. In an experiment with free cells
Oxygen supply is a critical point in technical processes when aerobic cells are used in immobilized preparations. This report concerns the use of hemoglobin or emulsions of perfluorochemicals (completely fluorinated organic compounds) to carry oxygen to immobilized cells. Both methods work well and do not seem to harm the cells. The perfluorochemical method of improving oxygen supply showed a high
The stability of biocatalysis in systems containing organic solvents is reviewed. Among the examples presented are homogeneous mixtures of water and water-miscible organic solvents, aqueous/organic two-phase systems, solid biocatalysts suspended in organic solvents, enzymes in reverse micelles and modified enzymes soluble in water immiscible solvents. The stability of biocatalysts in organic solve
