title: Enzyme distribution and matrix characteristics in biocatalytic particles.
abstract: In a study of Assemblase, an industrial immobilized penicillin-G acylase, various electron microscopic techniques were used to relate intra-particle enzyme heterogeneity with the morphological heterogeneity of the support material at various levels of detail. Transmission electron microscopy was used for the study of intra-particle penicillin-G acylase distribution in Assemblase particles of various sizes; it revealed an abrupt increase in enzyme loading at the particle surface (1.4-fold) and in the areas (designated halo's) surrounding internal macro-voids (7.7-fold). Cryogenic field-emission scanning electron microscopy related these abrupt local enzyme heterogeneities to local heterogeneity of the support material by revealing the presence of dense top layers surrounding both the particle exterior and the internal macro-voids. Furthermore, it showed a very distinct morphological appearance of the halo. Most probably, all these regions contained relatively more chitosan than gelatin (the polymers Assemblase was constructed of), which suggested local polymer demixing during particle production. A basic thermodynamic line of reasoning suggested that a difference in hydrophilicity between the two polymers induced local demixing. In the future, thermodynamic knowledge on such polymer interactions resulting in matrix heterogeneity may be used as a tool for biocatalyst design.
authors.affiliation: Department of Agrotechnology and Food Sciences, Food and Bioprocess Engineering Group, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands. Jeroen.vanRoon@wur.nl
authors.forename: J L
authors.initials: JL
authors.lastname: van Roon
authors.forename: R M
authors.initials: RM
authors.lastname: Boom
authors.forename: M A
authors.initials: MA
authors.lastname: Paasman
authors.forename: J
authors.initials: J
authors.lastname: Tramper
authors.forename: C G P H
authors.initials: CG
authors.lastname: Schroën
authors.forename: H H
authors.initials: HH
authors.lastname: Beeftink
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D020285:Cryoelectron Microscopy; D004800:Enzymes, Immobilized / Q000032:analysis / Q000737:chemistry / Q000648:ultrastructure; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D043942:Nanotubes / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D010399:Penicillin Amidase / Q000032:analysis / Q000737:chemistry* / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation; D013499:Surface Properties
chemical_list: D004800:Enzymes, Immobilized; D010399:Penicillin Amidase