Interaction of porphyrins with heme proteins--a brief review.

Two important porphyrins, protoporphyrin IX and hematoporphyrin IX, derivatives of which form the basis of photosensitization in the photodynamic therapy of cancer treatment, interact with two physiologically important heme proteins hemoglobin and myoglobin. The extent and modality of these interactions vary with the state of aggregation of the two porphyrins. Upon binding with these proteins, both the drugs change the protein conformations and release the heme-bound oxygen from the oxyproteins. At the same time, the peroxidase activities of these proteins are potentiated due to the protein-porphyrin complexation, as is found in case of horseradish peroxidase also. The effect of porphyrins on heme proteins should be given due consideration in elucidating the details of the mechanism of porphyrin actions in therapy.