This porphyrin is the precursor to hemoglobin, the oxygen carrier in animals, and chlorophyll, the dye in plants.

One mutation, a substitution of the amino acid tryptophan for arginine at position 59 (also written as Arg59Trp or R59W), is found in about 95 percent of South African families with variegate porphyria.

This buildup, in combination with nongenetic factors (such as certain drugs, alcohol and dieting), causes this type of porphyria.

Inhibition of protoporphyrinogen oxidase is a mechanism of action for several commercial herbicides including the nitrophenyl ethers acifluorfen and fomesafen and the pyrimidinediones butafenacil and saflufenacil.

The damage is caused by an accumulation of protoporphyrin IX in the plant cells by inhibiting protox within the tetrapyrrole biosynthesis pathway.