BETA-GALACTOSIDASE ACTIVITY AT THE LIPID-WATER INTERFACE: ARE THERE SEVERAL CONTROL LEVELS?

IVÁN CICLICK; JM SANCHEZ; ANAHÍ DEL V.TURINA; MARÍA A.PERILLO.

UNC-Cordoba, Argentina

Jornada; XII Jornadas Científicas de la SBC; 2001

Sociedad Biológica de Cordoba

We demonstrated that membrane adsorption or penetration differentially modulates b-galactosidase activity against soluble substrates (Sanchez & Perillo, Colloids & Surf., in press). In heterogeneous media, all the chemical species taking part in a chemical reaction would eventually interact with the surfaces available. The aim of the present work was to investigate if the partitioning of  ortho-nitro phenyl galactopyranoside (ONPG), ortho-nitro phenol (ONP) and E.coli b-galactosidase towards the membrane, represent  significant control levels to the enzyme kinetics, in addition to changes in the reaction intrinsic-mechanism at the lipid-water interface. Multilamellar vesicles of soybean phosphatidylcholine were used as model membranes. Membrane-water partition coefficients (Pm/w )  were determine according to the theory and methodology developed in our laboratory (Perillo & Arce, 1991, J.Neurosci.Meth.36:203). The values of Pm/w obtained (0, 50 and 118 for ONPG, ONP and enzyme respectively) were applied to a  two-compartments model, with freely accessible substrate and a nucleophile-like activatory effect exerted by the polar head groups in the membrane compartment, which partly reproduced the lipid concentration dependence we had observed in  Vmax .  Supported by grants from CONICET, SeCyT-UNC, Agencia Cordoba Ciencia and ANPCyT.