31P-NMR study of pig intestinal brush-border membrane structure: effect of zinc and cadmium ions.

31P-NMR experiments on intact pig small intestine brush-border membrane vesicles (BBMV) and detergent-solubilized membranes gave direct insights into the organization of the phospholipids (PL) and their interaction with zinc and cadmium ions. Various endogenous PL were identified from well resolved BBM micelle spectra. These experiments revealed a strong interaction of Zn2+ and Cd2+ with the negatively charged phosphatidylinositol and phosphatidylserine. In BBM micelles, a progressive time-dependent PL degradation occurred in the absence of ions and indicated the presence of active phospholipases. The presence of zinc inhibited the degradation process whereas cadmium had the opposite influence. 31P spectra of BBMV were carefully characterized. Neither zinc nor cadmium affected the PL bilayer structural organization. A degradation of PL, monitored by the increase of the inorganic phosphate (Pi) signal, also occurred in vesicles but to a lesser extent than in micelles. A 2/3 internal, 1/3 external PL asymmetry was observed in the absence and presence of ions.