Probing polyethylene glycol-phospholipid membrane interactions using enzymes

Interaction of polyethylene glycols (PEGs) with phospholipid membranes lead s to aggregation and fusion of membranes. The structural basis of these eve nts in membranes, especially in contact with low-molecular-weight PEGs, is uncertain. Using phsopholipases, a class of interfacially active enzymes, w e demonstrate enhanced accessibility of lipid hydrophobic portions in the p resence of PEGs. All three phospholipases, i.e., A(2), C, and D, show enhan cement of activity in the presence of PEGs. Enhancement of activity does no t depend on the size of the vesicle or the presence of proteins in the memb rane. Fluorescence quenching of probes buried in the membrane supports the phospholipase data. The utility of phospholipases as probes to monitor loca l and fine structural changes in the membranes is discussed, (C) 1999 acade mic Press.