Membrane topology modulates beta-galactosidase activity against soluble substrates |
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Authors: | Sanchez Julieta M Perillo Maria A |
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Institution: | Departamento de Química, Facultad de Ciencias Exactas, Fisicas y Naturales, Universidad Nacional de Cordoba, Av. Velez Sarsfield 299, 5000 Cordoba, Argentina. |
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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. |
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