title: Surface chemistry and spectroscopy of the β-galactosidase Langmuir monolayer.
abstract: The changes of interfacial properties of β-galactosidase introduced into different pH environments are investigated through surface chemistry and in situ spectroscopy. Conditions for an optimal Langmuir monolayer formation were firstly obtained by varying the subphase salt concentration and the surface-pressure area isotherm was used to extrapolate the limiting molecular area of the enzyme monolayer to be around 42,000 Å(2) molecule(-1). Surface pressure stability measurements held at 20 mN/m for 90 min along with compression-decompression cycles revealed no aggregate formation at the air-water interface. Consistent with the data obtained from the isotherm, in situ UV-Vis and fluorescence spectroscopy shows a steep rise in absorbance and photoluminescence intensity correlating to with a switch from a liquid-expanded to a liquid-condensed phase. A decrease in subphase pH increased the electrostatic repulsion as the enzyme was protonated, leading to an expanded monolayer. Infrared absorption-reflection spectroscopy demonstrates that the enzyme adopts mainly β-sheet conformation at the air-water interface before and during the compression.
authors.affiliation: Department of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33146, United States.
authors.forename: Nicholas F
authors.initials: NF
authors.lastname: Crawford
authors.affiliation: MP Biomedicals LLC, 3 Hutton Center, Santa Ana, CA 92707, United States; Department of Engineering Design Technology, Cerritos College, 11110 Alondra Boulevard, Norwalk, CA 92650, United States.
authors.forename: Miodrag
authors.initials: M
authors.lastname: Micic
authors.affiliation: MP Biomedicals LLC, 3 Hutton Center, Santa Ana, CA 92707, United States.
authors.forename: Jhony
authors.initials: J
authors.lastname: Orbulescu
authors.affiliation: MP Biomedicals SAS, Parc d'innovation-Rue Geiler de Kaysersberg, Illkirch-Graffenstaden 67402, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Weissbart
authors.affiliation: Department of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33146, United States. Electronic address: rml@miami.edu.
authors.forename: Roger M
authors.initials: RM
authors.lastname: Leblanc
mesh_terms: D000388:Air; D004795:Enzyme Stability; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D011312:Pressure; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D001616:beta-Galactosidase / Q000737:chemistry*
chemical_list: D014867:Water; D001616:beta-Galactosidase
keywords: Langmuir monolayer; Photophysical properties; Spectroscopy; β-Galactosidase