The influence of the fatty acid composition of Acholeplasma laidlawii membranes on the growth inhibitory activity of narasin, a polyether ionophorous antibiotic.

Narasin, apolyether ionophorous antibiotic capable of acting as a transmembrane carrier of cations, has a growth inhibitory effect on Acholeplasma laidlawii, permitting only 20% survival when present as 0.1 micrograms/ml in an undefined growth nutrient or fatty acid-deficient nutrient supplemented only with palmitic acid. When A. laidlawii is propagated in fatty acid-deficient nutrient supplemented with linoleic acid, however, the organisms become 40 times more sensitive to the growth inhibitory effect of this antibiotic. The actual fatty acid composition of the membranes would indicate that a higher degree of unsaturation enhances ionophore activity.