PHOTOFRIN PHOTOSENSITIZATION - CORRELATION OF PHOTOFRIN-ERYTHROCYTE BINDING PROCESSES WITH PHOTOLYSIS

Unilamellar suspensions of dimyristoylphosphatidylcholine (DMPC) can b e utilized to remove Photofrin from the erythrocyte. This enables corr elation of the Photofrin membrane-binding processes with Photofrin-sen sitized photolysis. The observed rates of erythrocyte binding as well as the observed rates of removal of Photofrin from the erythrocyte mem brane suggest the existence of two Photofrin species that differ in th eir rates of exchange between the erythrocyte and buffer phases. Selec tive depletion and readdition of these Photofrin species to the erythr ocyte membrane permits evaluation of their separate and joint photolyt ic efficiencies. These rapidly and slowly exchanging membrane-bound Ph otofrin species are separately much less efficient photosensitizers th an the two species together. The two Photofrin species exhibit essenti ally identical fluorescence emission spectra in the presence of DMPC. Nevertheless, models consistent with the results involve partitioning by chemically distinct Photofrin components or partitioning of chemica lly similar Photofrin components into distinct membrane environments, or a combination of these.