Rigid multilamellar bilayer cooperativity is modified by non covalently linked Neuraminic-5-acid: A spectrophotometric determination

By means of recording a simple serie of merocyanine 540 spectra, we present a method to calculate the value proportional to co-operative unit size of membranes (n). Our calculations, applied to different liposomal samples pro cessed in the presence or absence of sugars, in high or low ionic strength showed two main results. First, that any temperature cycling in high ionic strength of rigid DPPC bilayers will modify the membrane cooperativity. Sec ond, the presence of polysaccharide Neu-5-ac in solution will always produc e a strong drop in co-operativity of a rigid membrane of DPPC, whenever the negative charge is fully exposed. This last result indicates a differentia l ability of charged Neu-5-ac to disrupt a rigid membrane structure, even i n the absence of a covalent linkage and - remarkably in fully hydrated medi a.