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At least 19 recordsLinked to original sources
PubMed2000

The ratio between the fast and slow forms of bovine cytochrome c oxidase is changed by cholate or nucleotides bound to the cholate-binding site close to the cytochrome a3/CuB binuclear centre.

We determined the fraction of 'slow' and 'fast' conformations of bovine cytochrome c oxidase, following the kinetics of cyanide binding to the oxidized enzyme. We investigated whether treatment of heart mitochondrial particles with different commercially available types of cholate (standard and ultrapure) can affect the fraction of cytochrome c oxidase in the two states. Compared to standard cholate, the use of ultra-pure cholate for solubilization of heart mitochondrial particles significantly increased the fraction of the fast enzyme. Complete homogeneity (approximately 100% fast) was observed when cytochrome c oxidase was solubilized with ultra-pure cholate from heart mitochondrial particles pre-equilibrated with AMP; equilibration with ADP yielded a much smaller fraction of fast enzyme (approximately 35%). These observations are discussed on the basis of the structural relationships between the known cholate-binding site and the binuclear cytochrome a3-CuB site: variation in the occupancy of this binding site with cholate or nucleotides may modify reactivity of the oxidized binuclear centre towards cyanide.

Adenosine Diphosphate↗
PubMed1995

Cholate-induced disruption of calcitonin-loaded liposomes: formation of trypsin-resistant lipid-calcitonin-cholate complexes.

PURPOSE: The work was performed to obtain a better understanding why the oral administration of calcitonin (CT)-loaded liposomes to rats results in a hypocalcemia, while liposomes are normally disrupted in the gastro-intestinal tract and cannot protect the hormone from enzymatic digestion. METHODS: In vitro comparisons between the stability of calcein and CT-loaded liposomes in the presence of cholate solutions led to an interpretation of the results observed. By means of gel filtration, turbidimetry, and fluorescence measurements, the interactions between CT and lipids were studied after sonicated liposomes had been broken down by cholate. RESULTS: Experiments showed that CT in the external medium of a liposome suspension had no effect on the vesicles. Gel filtration of cholate-treated liposomes loaded with calcein and CT resulted in a total separation of calcein from the lipid fraction for detergent concentrations higher than 4 mM. However, 50% of the CT was reencapsulated even when the cholate-to-phospholipid molar ratio was increased up to 100. Incubation of cholate-solubilized liposomes with 1% trypsin resulted in a partial CT-breakdown. CONCLUSIONS: These results strongly suggest that during membrane solubilization by cholate, lipid-CT complexes are formed which retain most of the CT initially embedded in the liposomal membrane, and which offer some protection to CT under the action of trypsin. The existence of these complexes could be one of the reasons for the reported hypocalcemia in rats after oral administration of CT-loaded liposomes.

Animals↗
PubMed1978

Solubilization of napthalene by sodium cholate and pattern of self-association of sodium cholate in 0.15 M sodium chloride.

Naphthalene solubility was determined in aqueous 0.15 M NaCl containing sodium cholate in the 0-0.05 M concentration range at 25 +/- 0.1 degrees. Sodium cholate tends to self-associate in aqueous solutions. Most often, the association pattern has been described in terms of a monomer-micellar model in which it is assumed that no association occurs below the critical micelle concentration. By comparison of the experimental solubilization curve with curves calculated on the basis of the monomer-micellar model, it was shown that this model is inappropriate for the self-association pattern of sodium cholate. The solubility data were consistent with a model that assumes that sodium cholate associates to form dimers, trimers, and higher aggregates with an average aggregation number of 7.63. Model calculations suggest that naphthalene is solubilized by dimers and higher aggregates. Solubilization of naphthalene by trimers appears to be negligible.

Cholic Acids↗
PubMed2004

The effect of cholate on solubilisation and permeability of simple and protein-loaded phosphatidylcholine/sodium cholate mixed aggregates designed to mediate transdermal delivery of macromolecules.

Carriers for non-invasive administration of biologically important antioxidant enzymes Cu,Zn-superoxide dismutase (SOD) and catalase (CAT) were developed. Solubilisation and permeabilities of various soybean phosphatidylcholine/sodium cholate (SPC/NaChol) mixtures, mainly in the form of lipid bilayers, focussing on system properties relevant for non-invasive enzyme delivery were investigated in this work. Static and dynamic light scattering measurements gave information on the behaviour of the systems containing up to 40 mM NaChol and 30.6-1.2 mM SPC in the final suspension. The average size of such mixed aggregates was in the 100-200 nm range. Suspension turbidity decreased by 50% upon increasing nominal molar detergent/lipid ratio to NaChol/SPC = 7 and 1.25, in case of SPC = 1.2 and 19.6 mM, respectively. The effective NaChol/SPC molar ratio in bilayers saturated with the detergent was found to be: R(e)(sat) = 0.70 +/- 0.01; bilayer solubilisation point corresponded to R(e)(sol) = 0.97 +/- 0.02, independently of enzyme loading. Vesicles became very permeable to SOD when membrane bound NaChol concentration exceeded 13.7 mM, in case of total starting lipid concentration of 138 mM diluted to SPC = 19.6 mM. Specifically, we measured a 50% loss of SOD from the vesicles with an aggregate-associated molar detergent ratio NaChol/SPC approximately 0.7, which is near the saturation but well below the solubilisation limit. Calcein efflux from such vesicles was compared with SPC/NaChol/SOD mixed aggregates. Our results should contribute to the future design of vesicle mediated transdermal delivery of antioxidant enzymes.

Administration, Cutaneous↗
PubMed1990

Amiloride and taurine inhibit cholate-induced HCO3(-)-rich choleresis in perfused rat livers.

Bile acid-induced HCO3(-)-rich choleresis may be due to primary activation of sinusoidal Na(+)-H+ exchange or to biliary reabsorption of unconjugated bile acid. To test these hypotheses, we studied the effect of cholate and taurocholate (TC) (infused at 10 mumol/min for 20 min) on net H+ efflux, biliary [HCO3-], and bile flow in perfused rat livers and on intracellular pH (pHi) in isolated hepatocytes. Cholate, but not TC, produced HCO3(-)-rich choleresis. Amiloride and taurine decreased cholate-induced choleresis and HCO3- excretion and biliary excretion of unconjugated cholate. Amiloride, but not taurine, decreased cholate-induced net H+ efflux. Both cholate and TC (200-750 microM) decreased pHi. Cholate was metabolized to a polar compound, most likely cholate glucuronide, in the presence of amiloride. These results are consistent with the hypothesis that the biliary reabsorption of unconjugated cholate may be involved in HCO3(-)-rich choleresis. Amiloride also inhibited net hepatic uptake and biliary excretion of cholate and TC without affecting hepatic content of bile acids. It is suggested that amiloride may decrease the maximal excretion rate of cholate and TC. Since cholate and TC induce amiloride-sensitive net H+ efflux and decrease pHi, it appears that cholate and TC activate Na(+)-H+ exchange indirectly by decreasing pHi.

Amiloride↗
PubMed2003

Cyclosporin a and enterohepatic circulation of bile salts in rats: decreased cholate synthesis but increased intestinal reabsorption.

Cyclosporin A (CsA) has been shown to inhibit synthesis and hepatobiliary transport of bile salts. However, effects of CsA on the enterohepatic circulation of bile salts in vivo are largely unknown. We characterized the effects of CsA on the enterohepatic circulation of cholate, with respect to synthesis rate, pool size, cycling time, intestinal absorption, and the expression of relevant transporters in liver and intestine in rats. CsA (1 mg. 100 g(-1). day(-1) s.c.) or its solvent was administered daily to male rats for 10 days. Cholate synthesis rate and pool size were determined by a 2H4-cholate dilution technique. Bile and feces were collected for determination of cholate and total bile salts, respectively. Cycling time and intestinal absorption of cholate were calculated. The mRNA levels and corresponding transporter protein levels in liver and intestine were assessed by real-time polymerase chain reaction and Western analysis, respectively. CsA treatment decreased cholate synthesis rate by 71%, but did not affect pool size or cycling time. CsA reduced the amount of cholate lost per enterohepatic cycle by approximately 70%. Protein levels of the apical sodium-dependent bile salt transporter (Asbt) were 2-fold increased in distal ileum of CsA-treated rats, due to post-transcriptional events. In conclusion, chronic CsA treatment markedly reduces cholate synthesis rate in rats, but does not affect cholate pool size or cycling time. Our results strongly suggest that CsA enhances efficacy of intestinal cholate reabsorption through increased Asbt protein expression in the distal ileum, which contributes to maintenance of cholate pool size in CsA-treated rats.

Animals↗
PubMed1986

Hydroxyl/bile acid exchange. A new mechanism for the uphill transport of cholate by basolateral liver plasma membrane vesicles.

In order to characterize the driving forces for the concentrative uptake of unconjugated bile acids by the hepatocyte, the effects of pH gradients on the uptake of [3H]cholate by rat basolateral liver plasma membrane vesicles were studied. In the presence of an outwardly directed hydroxyl gradient (pH 6.0 outside and pH 7.5 inside the vesicle), cholate uptake was markedly stimulated and the bile acid was transiently accumulated at a concentration 1.5- to 2-fold higher than at equilibrium ("overshoot"). In the absence of a pH gradient (pH 6.0 or 7.5 both inside and outside the vesicle), uptake was relatively slower and no overshoot was seen. Reductions in the magnitude of the transmembrane pH gradient were associated with slower initial uptake rates and smaller overshoots. Cholate uptake under pH gradient conditions was inhibited by furosemide and bumetanide but not by 4, 4'-diisothiocyano-2,2'-disulfonic stilbene (SITS), 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (DIDS), or probenecid. In the absence of a pH gradient, an inside-positive valinomycin-induced K+ diffusion potential caused a slight increase in cholate uptake which was insensitive to furosemide. Moreover, in the presence of an outwardly directed hydroxyl gradient, uphill cholate transport was observed even under voltage clamped conditions. These findings suggest that pH gradient-driven cholate uptake was not due to associated electrical potentials. Despite an identical pKa to that of cholate, an outwardly directed hydroxyl gradient did not drive uphill transport of three other unconjugated bile acids (deoxycholate, chenodeoxycholate, ursodeoxycholate), suggesting that a non-ionic diffusion mechanism cannot account for uphill cholate transport. In canalicular vesicles, although cholate uptake was relatively faster in the presence of a pH gradient than in the absence of a gradient, peak uptake was only slightly above that found at equilibrium under voltage clamped conditions. These findings suggest a specific carrier on the basolateral membrane of the hepatocyte which mediates hydroxyl/cholate exchange (or H+-cholate co-transport). A model for uphill cholate transport is discussed in which the Na+ pump would ultimately drive Na+/H+ exchange which in turn would drive hydroxyl/cholate exchange.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1983

Taurocholate is more potent than cholate in suppression of bile salt synthesis in the rat.

Synthesis of bile salts is regulated through negative feedback inhibition by bile salts returning to the liver. Individual bile salts have not been distinguished with regard to inhibitory potential. We assessed inhibition of bile salt synthesis by either cholate or its taurine conjugate in bile fistula rats. After allowing synthesis to maximize, baseline synthesis was determined by measuring bile salt output in four consecutive 6-hr periods. Next, sodium cholate (+[(14)C]cholate) or taurocholate (+[(14)C]taurocholate) was infused into the jugular vein for 36 hr and bile was collected in 6-hr aliquots. Hepatic flux of exogenous bile salt was determined by measuring output of radioactivity in bile divided by specific activity of the infusate. Synthesis was determined during the last four 6-hr periods of infusion by subtracting exogenous bile salt secretion from the total bile salt output. Thirteen studies using cholate and 13 using taurocholate were performed. Hepatic flux of infused bile salt varied from 1 to 12 micro mol/100 g per rat per hr. Percent suppression of synthesis varied directly with hepatic flux of exogenous bile salt for both cholate and taurocholate in a linear fashion (r = 0.66, P < 0.01 and r = 0.87, P < 0.0005, respectively). Slope of the taurocholate line was 7.82 (% suppression/ micro mol per 100 g per hr), while slope of the cholate line was 3.66 (P < 0.05), indicating that taurocholate was approximately twice as potent as cholate in suppression of synthesis. At fluxes of 10-12 micro mol/100 g per hr, taurocholate suppressed synthesis 84 +/- 8 (SEM) % while cholate suppressed synthesis only 42 +/- 12% (P < 0.02). The x-intercept of the taurocholate line was 0.65 ( micro mol/100 g per hr), while that of the cholate line was -1.01 (NS) suggesting that the threshold for initial suppression of synthesis did not differ for these two bile salts. We conclude that taurocholate is a more effective inhibitor of hepatic bile salt synthesis than cholate, and that intestinal deconjugation of bile salts may play a role in the regulation of synthesis.-Pries, J. M., A. Gustafson, D. Wiegand, and W. C. Duane. Taurocholate is more potent than cholate in suppression of bile salt synthesis in the rat.

Animals↗
PubMed1990

Cholate uptake in basolateral rat liver plasma membrane vesicles and in liposomes.

The mechanism(s) and driving force(s) for hepatocellular uptake of the unconjugated bile acid cholate were investigated in isolated basolateral (sinusoidal) rat liver plasma membrane (blLPM) vesicles and in protein free liposomes. In blLPM vesicles both an inwardly directed Na+ gradient and a transmembrane pH difference (8.0 in/6.0 out) stimulated cholate uptake 2-3-fold above equilibrium uptake values (overshoot). While Na+ gradient driven cholate uptake could be inhibited by the anion transport inhibitor 4,4'-diisothiocyanato-2,2'-disulfonic acid stilbene (DIDS), the pH gradient dependent portion of cholate uptake was insensitive to DIDS, but could be inhibited by furosemide. Furthermore, initial rates (1-s values) of the pH gradient stimulated cholate uptake were linear with increasing substrate concentrations (no saturability). In liposomes a similar inside alkaline pH gradient also induced a transient DIDS insensitive/furosemide inhibitable intravesicular accumulation (approx. 2-fold) of cholate (overshoot). These findings confirm that hepatocellular uptake of cholate occurs in part via the common Na+/bile acid cotransport system. In addition, the data strongly indicate that in isolated membrane vesicles pH gradient driven cholate uptake represents nonionic diffusion rather than a carrier mediated process (Blitzer, B.L., Terzakis, C. and Scott, K.A. (1986) J. Biol. Chem. 261, 12042-12046). Since in the perfused liver DIDS inhibited uptake of both cholate and taurocholate to a similar extent, DIDS-insensitive pH gradient dependent membrane diffusion appears to be of minor significance for cholate uptake in the intact organ.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Relationship of hepatic cholate transport to regulation of intracellular pH and potassium.

Modulation of hepatic cholate transport by transmembrane pH-gradients and during interferences with the homeostatic regulation of intracellular pH and K+ was studied in the isolated perfused rat liver. Within the concentration range studied uptake into the liver was saturable and appeared to be associated with release of OH- and uptake of K+. Perfusate acidification ineffectually stimulated uptake. Application of NH4Cl caused intracellular alkalinization, release of K+ and stimulation of cholate uptake, withdrawal of NH4Cl resulted in intracellular acidification, regain of K+ and inhibition of cholate uptake. Inhibition of Na+/H(+)-exchange with amiloride reduced basal release of acid equivalents into the perfusate, initiated K(+)-release, and inhibited both, control cholate uptake and its recovery following intracellular acidification. K(+)-free perfusion caused K(+)-release and inhibited cholate uptake. K(+)-readmission resulted in brisk K(+)-uptake and recovery of cholate transport. Both effects were inhibited by amiloride. Interference with cholate transport through modulation of pH homeostasis by diisothiocyanostilbenedisulfonate (DIDS) could not be demonstrated because DIDS affected bile acid transport directly. Biliary bile acid secretion was stimulated by intracellular alkalinization and by activation of K(+)-transport. Uncoupling of the mutual interference between pH-dependent cholate uptake and K(+)-transport by amiloride indicates tertiary active transport of cholate. In this, Na+/K(+)-ATPase provides the transmembrane Na(+)-gradient to sustain Na+/H(+)-exchange which maintains the transmembrane pH-gradient and thus supports cholate uptake. Effects of canalicular bile acid secretion are consistent with a saturable, electrogenic transport.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1986

Structural changes in membranes of large unilamellar vesicles after binding of sodium cholate.

The interaction of the bile salt cholate with unilamellar vesicles was studied. At low cholate content, equilibrium binding measurements with egg yolk lecithin membranes suggest that cholate binds to the outer vesicle leaflet. At increasing concentrations, further bile salt binding to the membrane is hampered. Before the onset of membrane solubilization, diphenylhexatriene fluorescence anisotropy decreases to a shallow minimum. It then increases to the initial value in the cholate concentration range of membrane solubilization. At still higher cholate concentrations, a drop in fluorescence anisotropy indicates the transformation of mixed disk micelles into spherical micelles. Perturbation of the vesicle membranes at molar ratios of bound cholate/lecithin exceeding 0.15 leads to a transient release of oligosaccharides from intravesicular space. The cholate concentrations required to induce the release depend on the size of the entrapped sugars. Cholesterol stabilizes the membrane, whereas, in spite of enhanced membrane order, sphingomyelin destabilizes the membrane against cholate. Freeze-fracture electron microscopy and phosphorus-31 nuclear magnetic resonance (31P NMR) also reflect a change in membrane structure at maximal cholate binding to the vesicles. In 31P NMR spectra, superimposed on the anisotropic line typically found in phospholipid bilayers, an isotropic peak was found. This signal is most probably due to the formation of smaller vesicles after addition of cholate. The results were discussed with respect to bile salt/membrane interactions in the liver cell. It is concluded that vesicular bile salt transport in the cytoplasm is unlikely and that cholate binding is restricted to the outer leaflet of the canalicular part of the plasma membrane.

1,2-Dipalmitoylphosphatidylcholine↗
PubMedDate not supplied

Effect of cholate on H(+)-ATPase and other proteins of dog renal brush-border membrane.

A short treatment of dog renal brush-border membrane vesicles (BBMV) with sodium cholate, followed by dialysis of the detergent, reorients the polarity of H(+)-ATPase in the membrane and exposes its ATP binding sites to the extravesicular space, as previously shown with pig BBMV. In cholate-pretreated vesicles, the H(+)-ATPase remains fully active, but is inserted under the reversed polarity in sealed vesicles. A large spontaneous N-ethylmaleimide-sensitive ATPase activity is thus observed, as well as a steep intravesicular acidification upon external ATP addition, two findings absent in native vesicles. The ability of nitrate plus ATP to dissociate the hydrolytic subunits ot the proton pump in cholate-pretreated vesicles, but not in native vesicles, demonstrates that most of the ATP binding subunits are accessible to ATP following cholate treatment. The sensitivity of the cytoplasmic domain of the H(+)-ATP activity to trypsin also confirms the reorientation of the enzyme in cholate-pretreated vesicles. The H(+)-ATPase and alkaline phosphatase remain largely associated with the membranes after the treatment with cholate, but gamma-glutamyltranspeptidase, aminopeptidase N, and neutral endopeptidase are largely solubilized. Upon dialysis of cholate, all these enzymes are in part reinserted in the membrane according to their original polarity. The reorientation process is however specific for the H(+)-ATPase. Cholate treatment does not increase the formation of inside-out vesicles. Thus the treatment with cholate really reorients the polarity of the H(+)-ATPase in vesicles and allows for study of the proton pumping capacity of vacuolar H(+)-ATPase of proximal tubules.

Adenosine Triphosphate↗
PubMed1971

Fetal bile salt metabolism. I. The metabolism of sodium cholate-14C in the fetal dog.

Cholate metabolism was studied in fetal dogs 1 wk before term and was compared with cholate metabolism in adult dogs. Tracer amounts of sodium cholate-(14)C were administered to the fetus in utero by intravenous infusion over 6 hr. Fetal plasma disappearance, biliary excretion, tissue distribution, and placental transfer of cholate were measured over 10 hr. Infused cholate-(14)C was cleared rapidly from fetal plasma principally by the fetal liver and to a minor extent by placental transfer to the mother. The taurine conjugate was formed in the fetal liver and was excreted into the proximal small intestine via the biliary tree. Indirect evidence for the functioning enterohepatic circulation of bile salt in the fetus was obtained. Comparison with the results of similar experiments in adult dogs showed that the fetal liver was almost as efficient as the adult liver in the uptake, conjugation, and excretion of tracer amounts of cholate-(14)C. The maximal rate of excretion of radiolabel attained by the fetus was somewhat slower than in the adult (82.8 +/-1.4% and 96.1 +/-4.0% [mean +/-SE] of the infusion rate, respectively), and the proportion of the total dose excreted by the fetal liver during 10 hr was smaller (81.4 +/-1.3% vs. 96.6 +/-4.4%). This difference could be only partly accounted for by placental transfer (2.8 +/-0.6% of the fetal dose). Labeled cholate and taurocholate were excreted by the fetus at similar rates, which suggests that, under the conditions of study, conjugation had little influence on the rate of transfer of cholate across the liver cell. It is concluded that the fetal dog, 1 wk before birth, has a remarkably mature and efficient mechanism for the uptake and excretion of cholate.

Animals↗
PubMed2002

Cesium cholate: determination of X-ray crystal structure indicates participation of the ring hydroxyl groups in metal binding.

The crystal structure of cesium cholate, C(24)H(36)(OH)(3) COOCs has been determined with three-dimensional X-ray diffractometer data. It crystallized in the monoclinic space group P2(1) with unit-cell dimensions a = 11.543(5) A, b = 8.614(3) A, and c = 12.662(5) A, beta(deg) = 107.95(2), V = 1197.7 A(3) and Z = 2. The atomic parameters were refined to a final r = 0.0269 and R(omega) = 0.0280 for 2342 observed reflections. Each Cs(+) is coordinated to 7 oxygen atoms from 5 different cholate anions with Cs-O distances ranging from 2.957(4) A to 3.678(5) A. In this crystal, 5 cholates are coordinated with 1 Cs(+), and 5 Cs(+) are coordinated with 1 cholate anion. Carboxyl and all the 3 ring hydroxyl groups of cholate anion participate in binding to Cs(+) simultaneously, and there is no water molecule coordinated with the Cs(+). The pattern of successive rows arranged with polar (p) and non-polar (n) faces in apposition leads to the formation of a sandwich sheet structure with polar and non-polar channels. The Cs ions lie within the polar interior of the sandwich. The H-bond network is reorganized in forming cesium cholate from cholic acid. All the oxygen atoms in cholate anion are involved in H-bonding reciprocally or with water molecules to form an extensive 3-dimensional network of H-bonds. Compared with cholic acid and other similar type of steroids, the coordination structure and H-bonding of Cs cholate crystal are distinct.

Binding Sites↗
PubMed2003

Dietary cholate is required for antiatherogenic effects of ethanol in mouse models.

BACKGROUND: Human consumption of moderate amounts of ethanol is associated with reduced cardiovascular events. Studies examining the effect of ethanol on atherosclerosis in mouse models have yielded conflicting results that may be due to differences in dietary fat and cholate content. To determine if dietary cholate influences ethanol's effect on atherosclerosis, we fed apolipoprotein E-/- and low-density lipoprotein receptor (LDLR)-/- mice different liquid diets with or without ethanol. METHODS: Apolipoprotein E-/- mice were fed a low-fat or high saturated fat, cholate-containing diet with or without ethanol for 3 to 10 weeks, and LDLR-/- mice were fed a low-fat, high saturated fat, or high saturated fat diet with cholate with or without ethanol for 7 weeks. At the end of the feeding study, aortic root lesion size was determined and compared with serum cholesterol, triglycerides, and high-density lipoprotein cholesterol. Because dietary cholate increases hepatic nuclear factor (NF)-kappaB and ethanol inhibits NF-kappaB, we also examined the effect of ethanol on aortic NF-kappaB binding activity. RESULTS: Adding ethanol to a low-fat diet had no effect on lesion size. Similarly, ethanol had no effect on lesion size in LDLR-/- mice consuming a high saturated fat diet. Adding ethanol to a high-fat, cholate-containing diet for either strain resulted in a 25% to 50% reduction in lesion size. Dietary cholate increased and ethanol reduced NF-kappaB binding activity in the aorta. CONCLUSIONS: These results suggest that ethanol inhibits atherosclerosis in the presence of dietary cholate, which may occur via an anti-inflammatory mechanism.

Alcohol Drinking↗
PubMed1988

Characterization of complexes of egg yolk phosphatidylcholine and apolipoprotein A-II prepared in the absence and presence of sodium cholate.

Complexes of apolipoprotein A-II and egg yolk phosphatidylcholine were prepared in mixtures of different composition in the absence and presence of sodium cholate. By gradient gel electrophoresis, complex preparations were polydisperse and particle size distributions were influenced by the composition of the reconstitution mixture. Complexes generally exhibited a discoidal morphology by electron microscopy, but showed increased formation of vesicular complexes at elevated levels of egg yolk PC in the mixtures. By chemical crosslinking, complexes formed in the absence of cholate were shown to consist primarily of discoidal species with three apolipoprotein A-II molecules per particle in the mixtures investigated; complexes formed in the presence of cholate included species ranging from three to five apolipoprotein A-II per particle. The number of apolipoprotein A-II per particle and the sizes of the complexes, prepared in cholate, increased with increase of egg yolk PC in the reconstitution mixture. Relative to the particle size distribution of discoidal complexes formed in the absence of cholate, those prepared in cholate showed a distribution shifted to larger particle sizes. Complexes of similar particle size distribution formed in the presence or absence of cholate showed similar physical-chemical properties. Discoidal complexes with the same number of apolipoprotein A-II per particle but of different size and composition were observed, suggesting the possibility of some conformational adaptation of apolipoprotein A-II leading to stabilization of egg yolk PC bilayers of different diameter. Properties of particle size distributions of discoidal complexes prepared in cholate of apolipoprotein A-II and egg yolk PC were compared with those of complexes of apolipoprotein A-I previously reported (Nichols, A.V., Gong, E.L., Blanche, P.J. and Forte, T.M. (1983) Biochim. Biophys. Acta 750, 353-364).

Apolipoprotein A-II↗