Na cholate

Figure 2. Schematic view of proposed model for association of lecithin and Na cholate into mixed micelles...

For still larger quantities of water, one obtains the isotropic phase (IV), formed of mixed micelles. By extending the frontier line, WN, up to its intersection with side L-NaC of the triangle of the Figure 3, it can be seen that in order to get this micellar dispersion, at least one molecule of Na cholate is needed for two molecules of lecithin. 

Consider first the weight proportion of 77% of Na cholate for 33% lecithin which has to be reached in order to solubilize all the lecithin in water. This corresponds nearly to one molecule of Na cholate for two of lecithin. Taking as a model the one proposed in Figure 2, we can calculate the size which the mixed micelles should have so that the proportion of one molecule of Na cholate for two of lecithin will be obeyed. In other words, we want to know the number of lecithin molecules packed side by side which, surrounded by a ring of adjacent Na cholate molecules, can give the desired proportion. The calculation gives for each... 

For the proportion of one molecule of Na cholate to one of lecithin —i.e.y 37% Na cholate and 63% lecithin—the same calculation gives 24 molecules of lecithin for 24 of Na cholate in each layer—i.e., 48 molecules of each species for the whole of the mixed micelles and a molecular weight of about 60,000. Finally, for the weight proportion of 1 to 1 (about five molecules of Na cholate for three of lecithin), we find per layer 10 molecules of lecithin for 17 of Na cholate. This leads to 20 molecules of lecithin for 34 of Na cholate for the whole mixed micelle and a molecular weight of about 30,000. 

It is also reasonable to admit that the size of the mixed micelle could be the same in all systems situated along line OW since in all these cases the mixed micelles would always be in equilibrium with a micellar solution of pure Na cholate. Indeed, the chemical potential of the Na cholate in solution remains practically constant whatever the concentration, as long as micelles are present. Consequently, the chemical potential of the Na cholate attached to lecithin on the mixed micelles must also be constant since there is equilibrium. 

Although the values of the calculated dimensions of the mixed micelles agree with the order of magnitude of the measured values, it cannot be asserted that the molecules of Na cholate forming the ring around the mixed micelles necessarily touch each other. All that can be said is that as the free Na cholate in solution is at its maximum chemical potential (since the solution is micellar), the surface of the mixed micelles must be saturated by Na cholate, in the sense of a saturated solution of one component in or on the other. As this is an equilibrium, it seems obvious that there is a permanent exchange between the Na cholate molecules fixed on the surface of the mixed micelles and those free in solution. 

These statements lead to the conclusion that the limiting proportion of 1 gram of Na cholate associated to 1 gram of lecithin is simply imposed by the size of a certain form of mixed micelle which can remain in equilibrium with an excess of Na cholate in micellar solution. Thus, it clearly appears that association is governed by the necessity of securing the proper hydrophilic-lipophilic balance of the mixture of two components. Here, as in the case of other amphiphilic substances, by the progressive increase in proportion of the more hydrophilic amphiphile. the association can reach complete micellar dispersion in water. 

For mixtures of lecithin plus Na cholate it appears possible to infer the molecular arrangement in the dispersed micelles from the most likely structure of the liquid crystalline phase suggested by x-ray analysis. However, there are cases where dispersion is not possible because neither component is sufficiently hydrophilic to be dispersed even when alone in water. This is shown by the association of cholesterol and lecithin in the presence of water. The ternary diagram of Figure 4 is relative to these systems. Here only the lamellar liquid crystalline phase is obtained (region 1< in Figure 4). This phase is already given by lecithin alone, which can absorb up to 55% water. Cholesterol can be incorporated within this lamellar phase up to the proportion of one molecule of choles-... 

In the presence of an EOF, however, they migrate slowly towards the cathode. If now compounds are introduced into the capillary that interact with the SDS micelles, the mobility of these compounds will be influenced by the movement of the micelles to an extent that depends on the strength of this interaction. MECC is carried out using various forms of detergent anionic (e.g., SDS or Na-cholate), cationic (e.g., cetyltrimethylammonium bromide, CETB) and neutral (e.g., Triton X-100). 

Similar to Na cholate with the exception of no counterion-steroid OH bonding... 

Fig. 3A,B. Dissociation of a[ from of the lAP substrate. The first (A) and the second (B) peaks shown in Fig. 2A were separately incubated with [ SJGTPtS, MgCl2 at 30°C for 1 h and then applied to a TSK gel filtration column (HPLC). Proteins were eluted with 20 mM Hepes (pH 7.5), 1 mM EDTA, 1 mM dithio-threitol, 10 mM MgCl2, 100 mM Na2S04, 0.8% Na cholate. Adenylate cyclase activity ( ) and [ SIGTPtS binding (A) were measured as in Fig. 2. SDS-poly-acrylamide gel electrophoretic patterns of peak I and II proteins are shown on the right-hand side...

Proteoliposomes (0.25 mg protein 2.0 mg soybean phospholipids and 0.7 mg Na cholate) were preincubated for 20 min at 40 in 0.05 ml. (Pick, Packer, 1979) and were either added directly to the cuvette or passed through Sephadex G-50 (course) column (25x0.6 cm), and washed with a solution containing 20 mM Na-Tricine, pH 8 30 mM KCl, 3 mM MgCl2, 1 mM K phosphate and 10 nm valinomycin. Oxonol VI responses were measured as previously described (Shahak et al., 1982). The proteoliposome concentration in the reaction mixture was 0.125 mg protein/ml. 

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