Selective excitation of tryptophans in OmpF: a fluorescence emission study

The fluorescence studies of E. coli porin OmpF at pH 7.5 were carried out using excitation at 280 and 305 nm. Similar studies were performed in presence of a denaturant (urea) and a quencher (KI). Results show that both the tryptophans present in OmpF (residue numbers 61 and 214) contribute to fluorescence at 280 nm excitation, whereas only one residue shows fluorescence emission when excited at 305 nm. Based on these findings and the available crystal structure, it is speculated that tryptophan 61 of OmpF is selectively excited at 305 nm. The present studies point out some interesting features of the tryptophan microenvironments in OmpF.