Using the northern blot technique, the steady-state levels for the mRNAs encoding acyl-CoA oxidase, pristanoyl-CoA oxidase, trans2,3enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase multifunctional enzyme type 2, 3-ketoacyl-CoA thiolase and sterol-carrier-protein x during postnatal brain development were measured. The developmental patterns obtained for each mRNA species studied were similar, with an increase in the mRNA level between birth and postnatal day 5, followed by a gradual decrease to 34–55% of the maximal value at postnatal day 30. These results are in agreement with a coordinately controlled expression of the genes involved in VLCFA beta-oxidation during brain development. Moreover, comparison of these developmental profiles with that obtained for ceramide galactosyltransferase showed that the set-up of the very-long-chain fatty acids beta-oxidation system is independent of the myelinating signal in the central nervous system.

For a large number of specific applications, optical materials must be used in powder forms. In this context it has become highly necessary to characterize the optical and microstructural properties of such powders. Preliminary scattering experiments have shown that the scattering intensity from materials in powder forms could be quite different than that of the same homogeneous materials. In particular we have noted a strong increase in the level of the scattered light that could come from the bulk scattering. Here we show how to use the light scattering techniques in order to separate and determine the roughness and inhomogeneities of the samples. The same techniques are used to determine with accuracy the refractive index and absorption of the powders. In a second step, the same powders are evaporated in thin film forms, and we use classical spectrophotometric techniques to determine their refractive index and dispersion laws. The result are compared and discussed with those obtained with light scattering. In a general way, this study involves surface and bulk theories of light scattering, together with angle- resolved measurements, and atomic force microscopy.

We report here the effects of chemical fixatives on lipids studied under conditions simulating the immunogold labelling of phosphatidylserine. Using anti-phosphatidylserine antibodies, it is shown that the labelling intensity of a phosphatidyl-serine/phosphatidylcholine coating depends largely on the conditions of fixation. In fact, the usual aldehydic fixatives washed out most of the phostphatidylserine, thus preventing the binding of anti-phosphatidylserine antibodies. This was confirmed on biological samples such as rat liver and brain by measuring the loss of radiolabelled lipids during the fixation procedure. Furthermore, the complete procedure of tissue preparation for electron microscopical observation was investigated. The loss of (radiolabelled) lipids was studied in tissue samples during fixation and resin embedding. The results showed that the classical procedure (glutaraldehyde fixation followed by epoxy resin embedding) results in the loss of 73–91% of the tissue lipids whereas in unfixed, freeze-substituted samples, more than 76% of the tissue lipids are preserved.

Cerulenin analogues with 16 or 18 carbon atoms inhibit both ATP-dependent and acyl-CoA-dependent fatty acid elongations. Prior incubation of microsomes with inhibitors is necessary to obtain maximal inhibition. The analogues act on the first reaction of the elongation process catalysed by the 3-ketoacyl-CoA synthase. The 18-carbon analogue has no, or little, effect on the fatty acid synthesis, while cerulenin and its 16-carbon analogue totally inhibit this synthesis. The 18-carbon analogue appears to be a specific inhibitor of the synthesis of very long-chain fatty acids, with no effect on de novo fatty acid synthesis.

The mechanisms by which lipids are sorted and transferred to the plasma membrane are poorly understood as compared to the situation of glyco- proteins but are now under intense investigations particularly in animal cells (Van Meer 1989, Voelker 1991, Koval and Pagano 1991).

Three principal methods have been employed for the study of intracellular transport in nervous tissues: autoradiography associated with electron microscopy, time-staggered double-isotope labelling and isotopic pulse-chase experiments. Although the autoradiographical (Gould and Dawson, 1976; Gould et al., 1987; Kumara-Siri and Gould, 1980; Rawlins, 1973) and the double-labelling methods (Konat et al., 1985; Pereyra et al., 1983; Shimomura et al., 1984) can provide useful complementary information, only the isotopic pulse-chase experiments (Benjamins and Iwata, 1979; Burkart et al., 1982; Konat, 1981; Konat et al., 1985), associated with the use of intracellular transport inhibitors, would be able to demonstrate unambiguously the existence of intermembrane transfer events implicated in membrane biogenesis. No in vivo studies of peripheral nerves have been carried out using this method, most probably because of the difficulty in controlling the experimental conditions.

In this paper, we present different results obtained by the in vivo approach on the intracellular transport of lipids and fatty acids to the plasma membrane of seven-day-old etiolated leek seedlings. The complexity of the processes involved in plasma membrane biogenesis needs further investigations at both the molecular and cellular levels, but, at the cellular level, this complexity probably exceeds the possibilities of the in vivo analysis.Accordingly, a new approach, based on in vitro cell-free systems, which has proved to be suitable for studies on protein transport, was developped recently to study the membrane transfer of lipids. Some preliminary results concerning this new approach are presented and discussed.

A partially purified acyl-CoA elongase from leek epidermal cells is able to condense malonyl-CoA to long-chain acyl-CoAs. No strict specificity towards the chain lenght is observed in the C12C24 range. Oleoyl-CoA is also accepted by the elongase. The products are released from the elongase as acyl-CoAs. β-ketoacyl-CoA is formed as an intermediate during the elongation process. The existence of the β-ketoacyl-CoA was demonstrated after non-enzymatic decarboxylation leading to a 2-ketone characterized by TLC and radio GLC.

Abstract The effects of monensin on the intracellular distribution of neosynthesized lipids and fatty acids between different membrane fractions prepared from etiolated leek seedlings, were investigated. The penetration of the drug into the seedlings was measured after resolution of monensin by thin-layer chromatography with a solvent system consisting of hexane/diethyl ether/acetic acid (20:80:2, v/v). The concentration of monensin in the microsomal membranes as a function of the external monensin concentration was quantified. The effects of various amounts of the drug on lipid metabolism were studied to determine monensin concentrations having only slight effects on the overall lipid synthesis. Using such conditions, an accumulation of neosynthesized lipids was found in a subcellular membrane fraction enriched in Golgi membranes.

The immunoblotting procedure ascertains the presence of Po in the sciatic nerve of Trembler. In the 2-d-old mice, Po is detected in essentially similar amounts in Trembler and normal PNS, whereas its level in adult mutant sciatic nerves is never greater than 20% of the control. The sharp increase in Po levels observed during the third week in the normal nerves is not observed in those of the mutant;

We quantitated the content of the fatty acyl groups of sciatic nerves from normal and Trembler mice between the postnatal ages of 5 and 60 d. Palmitoyl, stearoyl, and unsaturated 18-carbon groups increased normally in Trembler nerves during the first 9 d, after which their levels were notably lower than those observed for the normal littermates. In good agreement, the synthesis of palmitic acid by the fatty acid synthetase was normal in the PNS of 9-d-old Trembler mice. "Myelin-specific" saturated very long chain fatty acyl groups (VLCFAG) were deficient at all ages studied, the deficiency increasing from about 2.5-fold at 5 d, to 26-fold at 60 d, compared to the maximal 3- to 4-fold decrease observed for the more ubiquitous shorter chains. The results presented in this paper suggest that the highly abnormal VLCFAG content of the mutant nerves cannot be accounted for by an abnormal fatty acid synthetase activity. For the fatty acyl chains with 18 carbon atoms, however, the deficiency observed after 9 d of age can be almost entirely explained by the diminished levels of palmitic acid. The relatively late occurrence of the palmitic acid deficiency compared with that of the VLCFAG and the normal palmitate synthetase activity observed in young mutant mice indicates that the former is an indirect consequence of the Trembler mutation.

Myelin and premyelin material denser than myelin were obtained from quaking (Qk), shiverer (Shi), and myelin-deficient (mld) mutant and control mice, using zonal centrifugation on zonal rotor. On these fractions, we performed biochemical analysis (lipids and fatty acid), and, in parallel, we determined the physical structure of membranes by the spin-label method. The hyperfine splitting constant (2 T11) was used to determine the order of membranes and their rigidity, and freqeuncy of rotation (V c) was used to measure fluidity.