formed during the last decades to unravel the mechanisms The binding of cytochrome c to liposomes was studied by electroof interactions between proteins and phospholipids. In fact, phoretic light scattering and dynamic light scattering measureknowledge of these interactions is paramount in understandments. Pure dimyristoylphosphatidylglycerol (DMPG) and dimying the functionality of the biological membrane. Therefore ristoylphosphatidylcholine (DMPC), as well as intramembranously it is well documented in literature that protein-lipid interacmixed DMPC-DMPG liposomal dispersions were investigated. tions strongly affect both the conformation and the catalytic Thus, the charge density of the liposomes was varied within a activity of enzymes [e.g., (2)]. Furthermore, recent work broad range. Because of adsorption of the protein onto the anionic performed in our laboratories, highlights the strong implicaliposome types, the electrophoretic mobility of the DMPG-contions of these interactions in setups of biotechnological reletaining liposomal dispersions was significantly reduced. These results confirmed the generally accepted model of interaction bevance in which proteoliposomes are used (3).
tween cytochrome c and phospholipids, which assumes the adsorp-
In studies dealing with protein-lipid interactions, cytotion process to be electrostatically controlled; however, the chrome c, a heme protein with an isoelectric point above experimentally observed charge reinversion phenomenon indi-pH 10 (4), has frequently been used as a model of a periphcated that some other type(s) of interaction(s) between phosphoeral protein and, accordingly, has been intensively studied lipids and cytochrome c seems to control the overall binding prousing a number of techniques (4-6). In general, cytochrome cess as well. From dynamic light scattering measurements it was c -liposomal membrane association has been considered an found that cytochrome c addition induced DMPG liposome aggreelectrostatically controlled process. Thus, Mustonen et al. gation. From the dependence of the aggregation kinetics on the (7) demonstrated that acidic phospholipids have to be prescytochrome c-to-phospholipid ratio, it was deduced that charge ent in the membrane for binding. Similarly, Snel et al. (8) neutralization was accompanied by bridging, especially at lower protein-to-DMPG ratios. แญง 1997 Academic Press reported that the amount of cytochrome c bound to mixed Key Words: cytochrome c; dimyristoylphosphatidylglycerol; didimyristoylphosphatidylglycerol (DMPG) -dimyristoylphosmyristoylphosphatidylcholine; liposomes; dynamic light scatterphatidylcholine (DMPC) liposomes increases on increasing ing; electrophoretic light scattering.
the amount of negatively charged DMPG. A further indication in favor of an important electrostatic component in the binding process is the fact that the cytochrome c -phospho-