Role of Phospholipids in Cell Function
A primary and essential role for phospholipids is defining the permeability barrier of the cell membrane and all internal organelles. However, due to the molecular diversity of phospholipids, individual phospholipid species must play a more dynamic role in cell function than simply defining the physical properties of the membrane. In addition to forming the membrane permeability barrier, phospholipids are intermediates in the synthesis of or direct precursors to other cellular components as well as regulatory molecules which affect cell physiology. Because of this pleiotropic requirement for phospholipids in maintaining normal cell function, it has often been difficult to assign a specific role to a particular phospholipid or group of phospholipids through in vivo studies. There are no direct assays for phospholipids function, as there are for enzymes, so the functions of individual phospholipids have come to light in many cases incidental to the study of a particular cellular process in vitro rather than by direct study of a particular phospholipid. In most cell types it is difficult to effect systematic and extensive alteration of the normal phospholipid composition which has made it difficult to verify in vivo the physiological significance of functions deduced from in vitro biochemical approaches alone. Utilization of classical genetic approaches has established the essential role of specific phospholipids for cell viability but has not provided a precise understanding at the molecular level for their requirement (Raetz and Dowhan, 1990). Application of more direct approaches of modern molecular genetics has made possible the design of mutants in which phospholipid metabolism and therefore phospholipid composition can be more precisely controlled (Dowhan, 1992). With such mutants it has been possible to establish new in vivo roles for phospholipids which has lead to biochemical studies to define the molecular basis for these functions.
KeywordsNADH Dehydrogenase Phospholipid Composition Phospholipid Metabolism Acidic Phospholipid DnaA Protein
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