FLUORESCENCE PROPERTIES OF ISOTROPICALLY AND ANISOTROPICALLY EMBEDDED FLAVINS

— On the basis of corrected fluorescence excitation and emission spectra, flavin photo-processes in anisotropically vesicle-bound flavins have been studied. By means of aliphatic C18H37-chains at positions 3, 7 and 10, the flavin nucleus can be variously anchored within the membrane/water interface (amphiflavin), thereby mimicking the various positions and microenvironments of the isoalloxazine ring in flavoproteins. From polarization spectra, the angles between the different electronic transition moments of isotropically dissolved or membrane-bound flavins have been obtained. Polarization and angle spectra of isotropically and various anisotropically embedded flavins exhibit strong differences, reflecting the specific interaction with the matrices. Based on a slightly modified theory, originally developed by Perrin and Weber, using the concentration dependence of fluorescence polarization, it is found that the radiative flavin-flavin interaction (selfcontact) on the membrane is by a factor of 25 to 54 smaller than in isotropic solution. This is taken as further justification to study anisotropic flavin chemistry on the basis of flavin-loaded vesicles.