Characterization of porphyrin interactions with peripheral type benzodiazepine receptors.

We have examined organ and species variations in interactions of porphyrins with peripheral-type benzodiazepine receptors and explored structure-activity requirements for porphyrin-receptor interactions. Whereas potency of the benzodiazepine RO5-4864 varies several orders of magnitude in competing for receptors in different organs and species, effects of porphyrins and the isoquinoline carboxamide PK11195 are relatively constant. The structural requirements determining porphyrin affinity for benzodiazepine binding sites are fairly strict. The most potent porphyrins are those with prominent physiological functions.