INCORPORATION OF CHOLESTEROL BY PLEUROPNEUMONIA-LIKE ORGANISMS

Abstract

Cholesterol is a necessary constituent of the culture medium for many pleuropneumonia-like organisms. Cholesterol-4C14 was shown to be removed from the supernatant medium by resting and growing cells and was found to be incorporated solely in the non-saponifiable lipid fraction, the major portion of which is located in the cell membrane. This distribution of non-saponifiable lipid was further verified by the lytic activity of digitonin on the cells containing sterol. The sterol is taken up by an irreversible adsorption process and can be removed only by solvent extraction. The initial adsorption process is affected by time, temperature, cell concentration, and pH, but not by respiratory poisons and destruction of protein end groups on the cell surface. Only steroids possessing a side chain similar to cholesterol are adsorbed, indicating that the adsorption of steroid occurs through the 8 carbon side chain. The uptake of sterol is relatively specific for pleuropneumonia-like organisms and osmotically stable L-forms. Some bacteria and osmotically labile L-forms also adsorb sterol but in a different manner and to a much lesser degree. The possible structural function of cholesterol is discussed.