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