Photofrin photosensitization. Correlation of Photofrin:erythrocyte binding processes with photolysis

Unilamellar suspensions of dimyristoylphosphatidylcholine (DMPC) can be utilized to remove Photofrin from the erythrocyte. This enables correlation of the Photofrin membrane-binding processes with Photofrin-sensitized photolysis. The observed rates of erythrocyte biding as well as the observed rates of removal of PHotofrin from the erythrocyte membrane suggest the existence of two Photofrin species that differ in their rates of exchange between the erythrocyte and buffer phases. Selective depletion and readdition of these Photofrin species to the erythrocyte membrane permits evaluation of their separate and joint photolytic efficiencies. These rapidly and slowly exchanging membrane-bound Photofrin species are separately much less efficient photosensitizers than the two species together. The two Photofrin species exhibit essentially 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 chemically similar Photofrin components into distinct membrane environments, or a combination of these.