OPTICAL MODULATION OF THE INSERTION OF GRAMICIDIN INTO BILAYER-LIPID MEMBRANES

Gramicidin A (gA) has been synthesized with a photoisomerizable azoben zene group linked to the C-terminus of the channel. Using single-chann el BLM measurements, we have demonstrated the effect; of irradiating a n optically gateable gramicidin on gramicidin channel conduction. A pa rallel study was carried out using UV and NMR spectroscopy of samples after dark adaptation, after exposure to UV between 330 and 340 nm, an d after exposure to white light. A ''photostationary'' state of 3:1 tr ans-cis was observed on exposure to white light. It was found that cha nnel formation was substantially increased after exposure to UV irradi ation and that this was reversed after dark adaptation. These results were consistent with a mechanism in which membrane insertion of azoben zene-linked gA was optically modulated.