DIACYLGLYCEROL AND HEXADECANE INCREASE DIVALENT CATION-INDUCED LIPID MIXING RATES BETWEEN PHOSPHATIDYLSERINE LARGE UNILAMELLAR VESICLES

Citation
A. Walter et al., DIACYLGLYCEROL AND HEXADECANE INCREASE DIVALENT CATION-INDUCED LIPID MIXING RATES BETWEEN PHOSPHATIDYLSERINE LARGE UNILAMELLAR VESICLES, Biophysical journal, 66(2), 1994, pp. 366-376
Citations number
41
Categorie Soggetti
Biophysics
Journal title
ISSN journal
00063495
Volume
66
Issue
2
Year of publication
1994
Pages
366 - 376
Database
ISI
SICI code
0006-3495(1994)66:2<366:DAHIDC>2.0.ZU;2-X
Abstract
Bovine brain phosphatidylserine (BBPS) vesicles were prepared with tra ces of dioleoylglycerol (18:1,18:1 DAG) or hexadecane (HD) to determin e the influence of changes in headgroup or acyl chain packing on dival ent cation-induced lipid mixing rates. A stopped-flow apparatus was us ed to combine vesicles with 3 mM Ca2+ or Ba2+. Aggregation was monitor ed by light scattering and lipid mixing by lipid probe dilution. Neith er 3-6 mol % 18:1,18:1 DAG nor up to 10 mol % HD significantly altered the BBPS chain melting temperature, vesicle diameter, or vesicle aggr egation rates. Lipid mixing rates doubled by adding either 3 mol % 18: 1,18:1 DAG or 6 mot % HD to BBPS with no change in the Ca2+ concentrat ion threshold. The Arrhenius slopes of the lipid mixing rates for cont rol, 3 mol % 18:1,18:1 DAG, and 6 mol % HD vesicles were identical. H- 2-nuclear magnetic resonance spectra of perdeuterated dipalmitoylglyce rol and HD in BBPS in the absence and presence of Ca2+ and Ba2+ showed that the solutes occupied different time-averaged positions in the bi layer under each condition. These data suggest that: 1) the enhanced l ipid mixing rate is related to the volume of the added alkyl chains; 2 ) 18:1,18:1 DAG and HD may alter the activation entropy or the attempt frequency at one or more steps in the lipid mixing process; 3) 18:1,1 8:1 DAG and MD are likely to act at a different spatial or temporal po int than the divalent cation; and 4) it is unlikely that the effect of these solutes on lipid mixing is due to their equilibrium time-averag ed positions in the bilayer. Others have shown that apolar lipids acce lerate fusion in nonbilayer phase-forming systems, but BBPS does not f orm these phases under these conditions. Therefore, we propose that th e effect of very small amounts of apolar substances may be very genera l, e,g., stabilizing the hydrophobic interstices associated with a var iety of proposed intermediate structures.