A fluorometric assay for measurement of protoporphyrinogen oxidase activity in mammalian tissue

The oxidation of protoporphyrinogen to protoporphyrin, which is catalyzed by the enzyme protoporphyrinogen oxidase, is an important step in heme biosynthesis. We describe a fluorometric assay for protoporphyrinogen oxidase activity in mammalian tissues which measures the conversion of the non-fluorescent protoporphyrinogen to the fluorescent protoporphyrin. Using these assay conditions, the mean level of protoporphyrinogen oxidase activity in sonicated rat liver mitochondria was 12.3, and in sonicated human cultured skin fibroblasts was 1.97 nmol protoporphyrin/mg protein/h.