Surfactant-coated enzyme

The most effective of these include immobilization [80], lipid coating [81], surfactant coating [82], use of cross-linked enzyme crystals [83], cross-linked enzyme aggregates [84], and membrane reactors [85]. 

Enzyme activity for the polymerization of lactones was improved by the immobilization on Celite [93]. Immobilized lipase PF adsorbed on a Celite showed much higher catalytic activity than that before the immobilization. The catalytic activity was further enhanced by the addition of a sugar or poly(ethylene glycol) in the immobilization. Surfactant-coated lipase efficiently polymerized the ring-opening polymerization of lactones in organic solvents [94]. 

In case of lipases, one of the simplest methods to combine an enzyme with an organic solvent is to coat the lipase with a lipid or surfactant layer before lyophilisation. It is estimated that about 150 surfactant molecules are sufficient for encapsulating one lipase molecule. Following this route the surfactant coated lipase forms reverse micelles with a minimum of water concentration. The modified lipases are soluble in most organic solvents, and the reaction rates are increased compared to the suspended hpases due to the interfacial activation [59,60]. 

Type I cells are alveolar lining cells that are involved with the transfer of substances from the alveolus through the wall to the blood. Type II cells are alveolar cells with two functions oxidative enzymes for lung metabolism, and the production and secretion of the surfactant coating the alveolar surface. 

Immobilized lipase showing high catalytic activity toward the macrolide polymerization was demonstrated.169 The immobilization of lipase PF on Celite greatly improved the rate of the DDL polymerization. Catalytic activity was further enhanced by the addition of a sugar or polyethylene glycol) (PEG) during immobilization. A surfactant-coated enzyme was used... 

Margolin, A. L., Novel crystalline catalysts, Trends Biotechnol., 14, 223-230, 1996. Goto, M., Kameyama, H. K., Goto, M., Miyata, M., and Nakashio, R, Design of surfactants suitable for surfactant-coated enzymes as catalysts in organic media, J. Chem. Eng. Jpn., 26, 109-111, 1993. 

Goto, M., Sumura, H., Abe, K., and Nakashio, R, Novel preparation method for surfactant-coated enzymes using W/O emulsion, Biotechnol. Tech., 9, 101-104, 1995. 

Mishima, K., and Matsuyama, K. (2000) Ring-opening polymerization of lactones using surfactant-coated enzymes in supercritical carbon dioxide. Chorinkai Saishin Gijutsu,... 

Free or immobilized enzymes have been exploited already in a number of systems. Here, biocatalysis may take place in reversed micelles or in an aqueous phase in eontaet with an organic solvent. In a powdered state some enzymes are able to funetion in pure organic solvents. Furthermore, modified enzymes such as polymer bound enzymes or surfactant-coated enzymes have been developed so that they ean solubilize in organie solvents to overcome diffusion limitation. The advantages of enzymatie reaetions using organic solvents can be briefly summarized as follows ... 

B. Surfactant-Coated Enzymes in Organic Solvents or Supercritical Fluids... 

The Okahata group has recently developed a new method to use surfactant-coated enzymes, which are freely soluble in organic solvents and show high catalytic activity in organic media. The surfactant-coated enzymes are prepared by the following very simple procedure [48]. Typically, the enzyme... 

FIG. 5 Schematic illustration of a surfactant-coated enzyme. (From Ref. 48.)... 

Therefore, it was proved that the surfactant-coated lipase could catalyze effectively and completely the glyceride synthesis in dry organic solvents, as compared with other enzyme systems, such as water-in-oil emulsion, enzyme dispersion, and PEG-grafted enzyme. 

FIG. 8 Typical time courses of transgalactosylation from lactose (10 mM) to 5-phe-nyl-l-pentanol (PI1C5OH, 1.0 mM) catalyzed by (a) the surfactant-coated P-D-galactosi-dase and (b) a native P-D-galactosidase from E. Coli, in an isopropyl ether-aqueous buffer two-phase system 30°C, 10 ml of isopropyl ether and 10 ml of buffer solution (0.01 M phosphate, pH 5.1), and [Enzyme] = 0.1 mg of protein. (From Ref. 52.)... 

These results indicate that SCCO2 is a good media for the catalytic reaction by the surfactant-coated enzymes, although several studies have reported no... 

FIG. 9 Time courses of transgalactosylation from l-0-/>-nitrophenyl-P-D-galactopyr-anoside (0.1 mM) to 5-phenylpentan-l-pentanol (1 mM) at 40°C catalyzed by P-d-galactosidase (1 mg of protein) in 10 ml (a) the surfactant-coated enzyme in SCCO2 with 150 atm, (h) the surfactant-coated enzyme in isopropyl ether, and (c) a native enzyme in scCOj with 150 atm. (From Ref. 53.)... 

Formation of surfactant coated starch nanopartides The loading of surfactant stabilized reverse micelles with starch nanospheres was studied. The surfactant-solvent systems used were AOT (sodium di-2-ethylhexylsulfosuccinate)/isooctane, CTAB (cetyl trimethyl ammonium bromideVchloroform and TritonX-100 (polyoxyethylene(10) isooctylphenylether)/toluene. These surfactants were selected due to their use by others for the solubilization of enzymes in reversed micelles(26-28). To load the reverse micelles, a concentrated (0.2Sg/mL) aqueous solution of starch nanospheres was added to the different surfactant/solvent pairs. The percent incorporation of starch in the nanospheres was determined based on the amount of the starch nanopartides that could be added to the surfactant/solvent system prior to the formation of a cloudy phase separated mixture. 

A pulsed system, called Time-Clock System, has been developed. It comprises a solid dosage form coated with a hydrophobie surfactant layer to which a water-soluble polymer is attached to improve adhesion to the core [66]. The thickness of the outer layer determines the time required to disperse in an aqueous environment. Following the dispersion of the outer layer, the eore becomes available for dispersion. An advantage is that eommon pharmaceutical excipients can be used to manufacture this system. Studies performed on human volunteers showed that the lag time was not affeeted by gastrie residence time. Furthermore, the dispersion of the hydrophobic film was not influenced by the presence of intestinal digestive enzymes or by the mechanieal aetion of the stomach. 

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