title: Water activity dependence of performance of surface-displayed lipase in yeast cells: a unique water requirement for enzymatic synthetic reaction in organic media.
abstract: Water activity (a(w)) is a crucial parameter affecting enzymatic synthetic reactions in organic media. In this paper, we report on the a(w) dependence of surface-displayed lipases, genetically immobilized on yeast cells via fusion with cell wall proteins. When Saccharomyces cerevisiae displaying Rhizopus oryzae lipase was used for esterification in n-hexane, equilibrating the dried cells with water prior to the reaction markedly increased the reaction rate. An equilibration of the cells with various saturated salt solutions showed that the reaction rate increased with increasing a(w) of the salt solution, to give the best performance at a(w) of 1.0. Interestingly, this trend was extremely different from those of lipases in powder or resin-immobilized form. To determine whether the cell surface is responsible for the unique a(w) profiles, an investigation was carried out similarly using other lipase sources and yeast strains, which indicated that, in all the cells examined, a higher a(w) resulted in a higher reaction rate. Moreover, increasing a(w) was found to increase the cell surface hydrophobicity determined by an aqueous-hydrocarbon biphasic partitioning assay. These results indicate that lipases displayed on yeast cells show a unique a(w) dependence probably because of the variation in cell surface characteristics.
authors: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan.
authors: Ayumi
authors: A
authors: Yoshida
authors: Shinji
authors: S
authors: Hama
authors: Kazunori
authors: K
authors: Nakashima
authors: Akihiko
authors: A
authors: Kondo
mesh_terms: D001709:Biotechnology / Q000379:methods*; D002473:Cell Wall / Q000201:enzymology*; D004951:Esterification; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D006586:Hexanes / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D008049:Lipase / Q000378:metabolism*; D009930:Organic Chemicals; D012233:Rhizopus / Q000201:enzymology / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D012997:Solvents; D013499:Surface Properties; D014867:Water / Q000737:chemistry / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D006586:Hexanes; D009930:Organic Chemicals; D012997:Solvents; D014867:Water; D008049:Lipase