title: Bubble-free oxygenation of a bi-enzymatic system: effect on biocatalyst stability.
abstract: The effect of bubble-free oxygenation on the stability of a bi-enzymatic system with redox mediator regeneration for the conversion of lactose to lactobionic acid was investigated in a miniaturized reactor with bubbleless oxygenation. Earlier investigations of this biocatalytic oxidation have shown that the dispersive addition of oxygen can cause significant enzyme inactivation. In the process studied, the enzyme cellobiose dehydrogenase (CDH) oxidizes lactose at the C-1 position of the reducing sugar moiety to lactobionolactone, which spontaneously hydrolyzes to lactobionic acid. 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt was used as electron acceptor for CDH and was continuously regenerated (reoxidized) by laccase, a blue multi-copper oxidase. Oxygen served as the terminal electron acceptor of the reaction and was fully reduced to water by laccase. The overall mass transfer coefficient of the miniaturized reactor was determined at 30 and 45 degrees C; conversions were conducted both in the reaction-limited and diffusion-limited regime to study catalyst inactivation. The bubbleless oxygenation was successful in avoiding gas/liquid interface inactivation. It was also shown that the oxidized redox mediator plays a key role in the inactivation mechanism of the biocatalysts unobserved during previous studies.
authors.affiliation: Research Group Environmental Organic Chemistry and Technology (ENVOC), Faculty of Bioscience Engineering, Department of Organic Chemistry, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium.
authors.forename: Wouter
authors.initials: W
authors.lastname: Van Hecke
authors.forename: Roland
authors.initials: R
authors.lastname: Ludwig
authors.forename: Jo
authors.initials: J
authors.lastname: Dewulf
authors.forename: Markus
authors.initials: M
authors.lastname: Auly
authors.forename: Tom
authors.initials: T
authors.lastname: Messiaen
authors.forename: Dietmar
authors.initials: D
authors.lastname: Haltrich
authors.forename: Herman
authors.initials: H
authors.lastname: Van Langenhove
mesh_terms: D052160:Benzothiazoles; D055162:Biocatalysis; D019149:Bioreactors; D002237:Carbohydrate Dehydrogenases / Q000737:chemistry* / Q000378:metabolism*; D004187:Disaccharides / Q000378:metabolism; D004795:Enzyme Stability; D042845:Laccase / Q000737:chemistry* / Q000378:metabolism*; D007785:Lactose / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D013451:Sulfonic Acids / Q000378:metabolism; D013844:Thiazoles / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D052160:Benzothiazoles; D004187:Disaccharides; D013451:Sulfonic Acids; D013844:Thiazoles; D014867:Water; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; C005608:lactobionic acid; D002237:Carbohydrate Dehydrogenases; C019859:cellobiose-quinone oxidoreductase; D042845:Laccase; D007785:Lactose; D010100:Oxygen