Binding of Hematoporphyrin Derivative to Human Serum Albumin

AbstractDialysis of hematoporphyrin derivative fraction A (HpD‐A) off human serum albumin at 38°C followed the Hill equation for cooperative binding with saturation at 5 to 8. 600 dalton porphyrin units. Approximately 15% of the HpD‐A was free for concentrations typical of human serum in photoradiation therapy. Possible structures of the tumor‐localizing and ‐photosensitizing component in HpD‐A are considered. Of these, a folded‐over, covalent dimer appears to be more consistent with the photophvsical properties.