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Photosensitization of Liposomal Membranes by Hematoporphyrin Derivative¹

Biophysics Laboratory, Physics Department, Illinois Institute of Technology, Chicago, Illinois 60616

The putative tumor-localizing and -photosensitizing fraction of hematoporphyrin derivative, the fastest migrating fraction of hematoporphyrin derivative separated by polyacrylamide gel filtration (HPD-A), photosensitized lipid peroxidation and membrane lysis in egg phosphatidylcholine liposomes. The rate of membrane damage was approximately 4-fold faster in oxygen compared to anoxia, with evidence for the involvement of singlet oxygen. The diffusion of HPD-A into small liposomes led to a shift of the Soret band from 363 nm in buffer to 398 nm accompanied by 4-fold enhancement of the fluorescence. The presence of human serum albumin retarded the diffusion of HPD-A into small liposomes, which is attributed to partial complexing of the HPD-A. A different effect of serum albumin was the protection of large liposomes from photosensitized lysis by incorporated HPD-A. This protection is attributed to scavenging of singlet oxygen, as evidenced by oxidation of tryptophan in the protein.

¹ Supported by NIH Grant GM 20117 and Department of Energy Contract AC0276EV02217. This is Publication DOE/EV/02217-48.

² To whom requests for reprints should be addressed, at Department of Physics, Illinois Institute of Technology, IIT Center, Chicago, Ill. 60616.

Received 6/ 1/83. Accepted 9/ 6/83.