Pheophorbide or phaeophorbide is a product of chlorophyll breakdown and a derivative of pheophytin where both the central magnesium has been removed and the phytol tail has been hydrolyzed. It is used as a photosensitizer in photodynamic therapy. Pheophorbide may be generated by digestion of ingested plant matter. Both worm (Caenorhabditis elegans) and mouse mitochondria are able to use the molecule in a form of ad hoc photoheterotrophy.
In chlorophyll a metabolism Pheophorbide is a product of chlorophyll breakdown and a derivative of pheophytin where both the central magnesium ion has been removed and the phytol tail has been hydrolyzed as plants senesce.
Further reactions within the enzymes pheophorbide a oxygenase and red chlorophyll catabolite reductase convert pheophorbide via a red catabolite into a fluorescent final product. The oxygenase is a Rieske protein containing an iron–sulfur cluster that requires reduced ferredoxin to function. The reductase also requires ferredoxin.
The fluorescent product can exist in two diastereomeric forms. All plants in a given genera produce a single isomer. An alternative breakdown pathway for pheophorbide involves the action of pheophorbidase. This enzyme hydrolyses the methyl ester, giving an acid which spontaneously decarboxylates to pyropheophorbide a:
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