Assay for enzymatic protoporphyrinogen oxidation, a late step in heme synthesis

Detailed directions are given for the spectrophotometric and fluorometric assays for protoporphyrinogen oxidation in rat liver mitochondria and other tissues. Linearity of the two assays with enzyme concentration is demonstrated. Some possible assay modifications and sources of error are mentioned. The fluorometric assay appears more sensitive, while the spectrophotometric assay may be more useful for assaying a wider variety of tissues. By both methods, rat liver mitochondria exhibit enzymatic oxidation at the rate of approximately 10 nmol protoporphyrin produced per hour per milligram protein.