Spontaneous phosphatidylcholine exchange between small unilamellar vesicles and lipid-apolipoprotein complexes. Effects of particle concentrations and compositions

Adipocyte fatty acid binding protein (A-FABP) is a 15-kDa protein found in high abundance in the cytosol of adipose cells. To better understand the role of this protein in intracellular free fatty acid (ffa) transport, the mechanism of ffa transfer from A-FABP to model membranes was examined by monitoring the transfer of fluorescent anthroyloxy ffa (AOffa) to small unilamellar phospholipid vesicles, using a resonance energy transfer assay. Structural features of ffa that increase aqueous solubility, such as shorter chain length and unsaturation, did not increase the AOffa transfer rate. In addition, solution conditions that increase the aqueous solubility of ffa, such as decreasing ionic strength and increasing pH, had little effect on AOffa transfer from A-FABP to membranes. These results suggest that AOffa do not transfer through the aqueous phase. The small entropic contribution to the free energy of the transfer process provides further evidence that AOffa may not travel through the surrounding aqueous environment when transferred from A-FABP to phospholipid membranes. Finally, the rate of AOffa transfer from A-FABP was directly dependent on the concentration of the acceptor membranes. These studies suggest that AOffa transfer from A-FABP to phospholipid vesicles may occur via transient collisional interactions between the protein and membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Section: Discussionmentioning

confidence: 94%

Mechanism of fluorescent fatty acid transfer from adipocyte fatty acid binding protein to membranes

Wootan¹,

Bernlohr²,

Storch³

1993

“…Several other studies in the literature have demonstrated lipid transfer to be dependent on concentration under a variety of experimental conditions (Jonas & Maine, 1979;Petrie & Jonas, 1984; Mütsch et al, 1986;Nichols, 1988). Nichols and Pagano (1981) have shown that concentration-dependent transfer can arise in the absence of vesicle interactions if monomer association rates are different for donor and acceptor vesicles.…”

Section: Discussionmentioning

confidence: 97%

Mechanism of spontaneous, concentration-dependent phospholipid transfer between bilayers

Jones¹,

Thompson²

1990

116

We have previously demonstrated that spontaneous phospholipid transfer between bilayer vesicles at higher vesicle concentrations is characterized not only by a first-order desorption rate but also by a second-order process dependent on vesicle concentration (Jones & Thompson, 1989b). We have extended our studies to examine the mechanism of this second-order process by investigating transfer as a function of lipid type, temperature, aqueous medium composition, and vesicle size. The results suggest a mechanism of concentration-dependent transfer in which the rate of lipid monomer desorption from vesicle bilayers is enhanced in transient vesicle-vesicle complexes.

“…0006-2960/88/0427-3925$01.50/0 © 1988 American Chemical Society The transfer of phospholipids has been measured between phospholipid vesicles (Martin & McDonald, 1976;Papahadjopoulos et al, 1976; Duckwitz-Peterlein et al, 1977;Kremer et al, 1977a;Roseman & Thompson, 1980; Nichols & Pagano, 1981 McLean & Phillips, 1981DeCuyper et al, 1983DeCuyper et al, , 1985, between lipoproteins (Jonas & Maine, 1979;Massey et al, 1982aMassey et al, ,b, 1984Petrie & Jonas, 1984), and between cellular membranes (Stuhne-Sekalec & Stanacev, 1982; Rindlisbacher & Zahler, 1983;Ferrell et al, 1985;Mütsch et al, 1986). In most of the systems studied, spontaneous phospholipid transfer has been shown to occur by soluble monomer diffusion through the aqueous phase.…”

mentioning

confidence: 99%

“…In most of the systems studied, spontaneous phospholipid transfer has been shown to occur by soluble monomer diffusion through the aqueous phase. However, in a few cases, transfer appears to occur by a collision-dependent mechanism (Jonas & Maine, 1979;Stuhne-Sekalec & Stanacev, 1982;Petrie & Jonas, 1984;Mütsch et al, 1986).…”

mentioning

confidence: 99%

Phospholipid transfer between phosphatidylcholine-taurocholate mixed micelles

Nichols¹

1988

The transfer of fluorescent-labeled N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (N-NBD-PE) between phosphatidylcholine-taurocholate mixed micelles was measured by monitoring the increase in fluorescence as N-NBD-PE, initially contained in mixed micelles at self-quenching concentrations, was diluted into unlabeled mixed micelles. The half-times for transfer of a homologous series of N-NBD-PEs differing in saturated acyl chain length from 11 to 16 carbons increased with acyl chain length from 4 to 35 s. The half-times for transfer of the same N-NBD-PEs between phosphatidylcholine vesicles without taurocholate were 200-6000 times slower than those between the mixed micelles. A kinetic analysis of initial transfer rate data was used to determine the mechanistic model that best described the data. According to this analysis, the increased rate of intermicellar phospholipid transfer relative to that of intervesicular transfer is a result of (1) exchange between micelles during transient micelle collisions which is not observed between vesicles and (2) an increased rate of monomer diffusion due to a faster rate of phospholipid dissociation from mixed micelles into the water phase than from vesicles. The relative significance of dissociation from mixed micelles into the water phase than from vesicles. The relative significance of collision-dependent versus monomer diffusion transfer increases with acyl chain length and hydrophobicity.