THE PROPERTIES OF ION CHANNELS FORMED BY THE COUMARIN ANTIBIOTIC, NOVOBIOCIN, IN LIPID BILAYERS

The coumarin antibiotic novobiocin forms ion channels of varying condu ctances in lipid bilayers. The conductances (about 20, 22, 14, 7 and 2 pS for 100 mM NH4Cl, CsCl, KCl, NaCl and LiCl, respectively) and sele ctivities (cation transference numbers in the range of 0.97-0.98) of o ne type of novobiocin-induced channel are similar to those found for c hannels formed by gramicidin A, an antibiotic of very different struct ure. The conductance of novobiocin channels of this type was independe nt of the species of the membrane lipid. This observation suggests tha t novobiocin molecules directly form these channels, and that channels are not formed through defects in lipid structure. The similarity in conductance and ion selectivity between channels induced by novobiocin and those formed by gramicidin A suggests that these structurally dif ferent molecules form channels with comparable internal diameter and i nternal surface charge distribution. Using HPLC purification we argue that the channel-forming activity of novobiocin is related to the acti vity of the novobiocin molecule itself, and not to a contaminant of th e commercially available novobiocin sodium salt preparation.