title: Membrane topology modulates beta-galactosidase activity against soluble substrates.
abstract: The effect of bio-surfaces of contrasting curvature, on the kinetic parameters of ortho-nitrophenyl-beta-D-galactopiranoside hydrolysis catalyzed by E. coli beta-galactosidase, was investigated. The self-aggregating state and structure of the amphiphiles (Phosphatidylcholine, Lubrol-PX, Triton X-100, DocNa, SDS and CTAB) were inferred from their c.m.c. values and light-scattering measurements. Low curvature phosphatidylcholine or mixed phosphatidylcholine-detergent vesicles increased V(max) without affecting K(M). High curvature micellar structures containing ionic detergents modulated negatively the enzyme activity (decreased or abolished V(max) and increased K(M)). Neither micelles containing non-ionic detergents nor the amphiphiles in a monomeric form, affected enzyme activity. CTAB at a concentration below its c.m.c but incorporated into a bilayer, became an activator (K(M) decreased respect to the control). Non-enzymatic interfacial hydrolysis of the substrate was discarded. Enzyme-membrane interaction and membrane elasticity, were evaluated using monomolecular layers at the air-water interface. Beyond particular molecular structures, topology affected the direction of the modulatory effects exerted by these amphiphiles on beta-galactosidase activity.
authors.affiliation: Departamento de Química, Facultad de Ciencias Exactas, Fisicas y Naturales, Universidad Nacional de Cordoba, Av. Velez Sarsfield 299, 5000 Cordoba, Argentina.
authors.forename: Julieta M
authors.initials: JM
authors.lastname: Sanchez
authors.forename: Maria A
authors.initials: MA
authors.lastname: Perillo
mesh_terms: D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology; D007700:Kinetics; D008027:Light; D008081:Liposomes / Q000737:chemistry; D008567:Membranes, Artificial; D009596:Nitrophenols / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D012542:Scattering, Radiation; D012995:Solubility; D013499:Surface Properties; D013816:Thermodynamics; D001616:beta-Galactosidase / Q000737:chemistry*
chemical_list: D002593:Cetrimonium Compounds; D008081:Liposomes; D008567:Membranes, Artificial; D009596:Nitrophenols; D010713:Phosphatidylcholines; D001616:beta-Galactosidase; D000077286:Cetrimonium