THE LIPIDS - MORE AND MORE ACTIVE AGENTS OF CELLULAR LIFE

Lipids, in living systems, do not only simply constitute an hydrophobi c matrix allowing the separation of the different aqueous compartments . Researchs in the field, for the last twenty years, have first demons trated that some lipids are playing an highly dynamic role in cellular signalling processes. It is, for example, the case of the phosphoryla ted derivatives of phosphatidylinositol but also of number of other li pids as phosphatidic acid, diacylglycerol or ceramides... These lipids are now considered as true ''seconder messengers''. On the other hand , it was demonstrated that fixation of some fatty acids or some lipids to proteins through covalent bonds, play a major role in regulating t he interactions of these proteins with membranes, Finally, application of methods as circular dichroism, magnetic nuclear resonance or X-ray diffraction for analysis of crystallized biological structures, have lead to the demonstration of highly specific inter-action between lipi ds and proteins inside the membranes themselves, All these aspects of lipid functions are analyzed in this paper.