Measurement of protoporphyrinogen oxidase activity.

Protoporphyrinogen oxidase catalyzes the oxidation of protoporphyrinogen to protophyrin. It is a membrane-bound mitochondrial enzyme and it is the target of photobleaching herbicides. The basic assay presented in this unit for measuring oxidase activity is based on oxidation of the colorless, nonfluorescent substrate, protoporphyrinogen, to the colored, fluorescent protophyrin. Alternate protocols are provided for the measuring the accumulation of protoporphyrinogen resulting from a decrease in oxidase activity due to treatment with diphenyl ether herbicides or oxidase inhibitor.