Role of membrane sterols in Mycoplasma capricolum.

A low level of cholesterol in lanosterol-rich membranes of Mycoplasma capricolum exerts a synergistic effect on growth while leaving the bulk physical state of the membrane unchanged. This observation has led to the proposal that cholesterol may serve a dual role in membranes: one as a bulk component and another of a more specialized nature involving cholesterol-specific interactions. Lanosterol, while competent as a bulk membrane sterol, cannot effectively perform the second function. The fact that a low level of cholesterol in lanosterol-rich cells specifically alters the ability of these cells to incorporate unsaturated fatty acids suggests that this more specialized role for cholesterol may be concerned with fatty acid transport or phospholipid biosynthesis.