Coproporphyrinogen III oxidase assay.

An assay for coproporphyrinogen oxidase activity is described which uses a [14C]-coproporphyrinogen substrate with product isolation by methylation, extraction, and thin layer chromatography. This method affords high sensitivity, since a high specific activity of the substrate and good reproducibility due to the incorporation of an internal standard can be obtained. The activity in rat liver and human lymphocytes was found to be 140 nmol protoporphyrin/h/g of liver and 483 pmol protoporphyrin/h/mg of lymphocyte protein, respectively.