The properties of ion channels formed by the coumarin antibiotic, novobiocin, in lipid bilayers.

The coumarin antibiotic novobiocin forms ion channels of varying conductances in lipid bilayers. The conductances (about 20, 22, 14, 7 and 2 pS for 100 mM NH4Cl, CsCl, KCl, NaCl and LiCl, respectively) and selectivities (cation transference numbers in the range of 0.97-0.98) of one type of novobiocin-induced channel are similar to those found for channels formed by gramicidin A, an antibiotic of very different structure. The conductance of novobiocin channels of this type was independent of the species of the membrane lipid. This observation suggests that 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 different molecules form channels with comparable internal diameter and internal surface charge distribution. Using HPLC purification we argue that the channel-forming activity of novobiocin is related to the activity of the novobiocin molecule itself, and not to a contaminant of the commercially available novobiocin sodium salt preparation.