Addition Of Sodium Oleate Research Articles

Phosphoinositide reorganization in human erythrocyte membrane upon cholesterol depletion.

The effect of cholesterol depletion on the activity of phosphatidylinositol/phosphatidylinositol 4-phosphate and diacylglycerol kinases and polyphosphoinositide phosphodiesterase has been studied in isolated membranes of human normal and cholesterol-depleted erythrocytes. Polyphosphoinositide synthesis (phosphatidylinositol/phosphatidylinositol 4-phosphate kinase activities) were found to depend on the permeability and sidedness characteristics of the membrane vesicles, which could limit the accessibility of ATP for the enzymes. When measured under proper conditions, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate synthesis were decreased in cholesterol-depleted membranes as compared with control membranes. The same level of synthesis could be obtained in both membranes by the addition of phosphatidylinositol (and Triton X-100) or of phosphatidylinositol 4-phosphate. Phosphatidic acid synthesis (diacylglycerol kinase activity) was also decreased in cholesterol-depleted membranes as compared with control membranes when measured in the presence of Ca2+. Addition of diolein (and Triton X-100) caused a large increase in phosphatidic acid synthesis which reached approximately the same level in both membranes. This showed that the apparent inhibition of polyphosphoinositide and phosphatidic acid synthesis was not due to a loss or to an inactivation of the kinases. Ca2+-activated polyphosphoinositide phosphodiesterase promoted the hydrolysis of 65-70% of the polyphosphoinositides in control and of only 45-55% in cholesterol-depleted membranes without changing the Ca2+ concentration for half-maximum hydrolysis (1 microM). Upon addition of sodium oleate, the extent of polyphosphoinositide hydrolysis became identical in both membranes, indicating again that there was no loss nor inactivation of the polyphosphoinositide phosphodiesterase in the cholesterol-depleted membranes. Since the concentration of the polyphosphoinositides was not changed by cholesterol depletion [Giraud, M'Zali, Chailley & Mazet (1984) Biochim. Biophys. Acta 778, 191-200], the reduction in both their synthesis and degradation observed here could be attributed to a reorganization of the phosphoinositides in membrane domains where they were not accessible to the kinases and phosphodiesterase. The reduction in phosphatidic acid synthesis was likely caused by a reduction in the total amount of the substrate diacylglycerol in cholesterol-depleted membranes as already shown [Giraud, M'Zali, Chailley & Mazet (1984) Biochim. Biophys. Acta 778, 191-200].

Stimulation of fatty acid methylation in human red cell membranes by phospholipase A 2 activation

Nonpolar methylated products comprise approximately 50% of the radioactive material extractable into Chloroform/methanol after incubation of human red cell membranes with S-[ methyl- 3 H]adenosylmethionine. One of these nonpolar products is fatty acid methyl ester. The enzyme which synthesizes fatty acid methyl ester had an apparent K m for S-adenosylmethionine of about 0.6 μM and a V max of about 0.6 pmol/mg protein per 30 min. Half-maximal activity was achieved upon addition of about 20 μM sodium oleate. Of the fatty acids tested, sodium oleate increased activity most effectively (6-fold) and arachidonic acid was ineffective. Evidence indicated that fatty acid methylation takes place on the cytoplasmic side of the plasma membrane. The reaction was demonstrable in intact cells incubated with [methyl- 3H]methionine, and increased upon addition of sodium oleate. Incubation of intact cells with melittin, a potent membrane phospholipase A 2 activator from bee venom, increased fatty acid methylation several-fold. Fatty acid methylation appears to be one of the consequences of phospholipase A 2 action in plasma membranes.

Electrochemical potential of magnetite during flotation

1. The authors show the dependence of the electrochemical properties of magnetite on the thickness of the layer removed from the specimen surface; this is of scientific interest, because the results obtained enable one to determine the effective conditions for preparation of solid electrolytes and to refine the experimental procedure so as to obtain reproducible data. 2. The variation of the magnetite electrode potential with the pH of the medium practically follows the same pattern as that characterizing magnetite-hematite equilibrium. 3. Addition of sodium oleate shifts the electrode potential toward the more negative region as a result of adsorption of the flotation reagent, the maximum change in potential being observed at pH 6–7, which also corresponds to maximum flotability of magnetite.

Site of free-fatty-acid inhibition of lipolysis by human adipocytes

When human adipocytes were incubated in albumin-free buffer, isoproterenol failed to stimulate an increase in either cyclic AMP or glycerol release. Cells incubated for 1 2 hr with 4% albumin and isoproterenol had a striking increase in cyclic AMP; this effect was markedly reduced when FFA concentration was increased by the addition of sodium oleate. When incubation was prolonged to 4 hr, the cyclic AMP concentration of stimulated cells fell towards the basal level. This decline in the level of cyclic AMP was prevented by frequent change in buffer. The ability of epinephrine and sodium fluoride to stimulate the adenylyl cyclase of human adipocyte membranes was not affected by the addition of sodium oleate. However, when intact cells were preincubated for 1 hr with added sodium oleate, the responsiveness to epinephrine of membranes derived from the cells was reduced. No such alternation in responsiveness to sodium fluoride occurred. These results indicate that the inhibitory effect of FFA on lipolysis is associated with a reduced production of cyclic AMP; the latter effect may be the consequence of FFA inhibition of adenylyl cyclase.

SURFACE TENSION OF SERUM

1. The equilibrium of the serum corresponding to its normal minimal surface tension is as stable and difficult to break, under ordinary conditions, as the osmotic tension equilibrium. The addition of a strong surface-active substance (sodium oleate, glycocholate, or taurocholate), will not lower it definitely, unless the substance is present in large amounts and in solution. After the first rapid drop has occurred, a process of recovery takes place, which brings back the normal surface tension in a short time (from 2 to 6 minutes in the case of pure serum). As a drop in the surface tension of the serum of animals may be very injurious to the red cells, this process of recovery is a normal one of defense in all cases in which surface-active substances (bile) are set free in the blood. 2. When diluted, the serum shows the same phenomenon to a smaller extent; the time of recovery is very much longer and the final surface tension is always lower than the original value. At a dilution of 1/10,000, no recovery takes place, the dilution being too high to overcome the lowering action of 1/10,000 of sodium oleate. 3. The recovery is stronger when the surface-active substance is added powdered or in a highly concentrated solution, and not stirred. 4. The recovery does not seem to be inversely proportional to the concentration of sodium oleate, when added superficially. Doubling the concentration at 1/2,000, for example, gives the same curve of recovery. This happens under certain conditions; namely, when the liquid is not stirred after the addition of sodium oleate. 5. This recovery is due to a purely physical phenomenon, namely adsorption, and is not specific for the serum. Other colloidal solutions, such as gum arabic, egg albumin, gelatin, and silver and gold sols, show it, only to a smaller degree. The process of recovery follows a logarithmic law in all cases, expressed by an equation of the form See PDF for Equation 6. Temperature affects this phenomenon. At first it enhances it, but finally decreases it. This would seem to connect the loss of the property of the serum known as complement in a serum with a modification of the physical properties of this serum. This phenomenon is being investigated further.