Extracellular lipids of yeasts.

Although lipids were among the first natural products to be examined in detail (30), their study lagged far behind that of the proteins and carbohydrates for over a century. This neglect was due in large part to the unattractive physical properties of the lipids, which sometimes rendered impossible, and always very tedious, the isolation of these products in a state of purity meeting the strict requirements of the chemist. This unfavorable situation began to change after World War II with the development of elegant new methods for the separation, analysis, characterization, and structural determination of organic compounds. At about the same time, there was an abandonment of the old view that the only function of importance for lipids was their role as long-term storage materials. This restricted outlook was replaced by recognition of the great significance of minor lipid constituents (41), such as phospholipids, sphingolipids, and lipoproteins, some of which were finally becoming available in the pure state as a result of the advances in technique. This combination of a fresh viewpoint and improved laboratory practice resulted in a resurgence of interest in lipid