A high-performance-liquid-chromatographic method for the assay of coproporphyrinogen oxidase activity in rat liver

An h.p.l.c. method was developed for the assay of coproporphyrinogen oxidase activity in rat liver. The protoporphyrinogen IX formed is completely oxidized to protoporphyrin IX for separation and quantification by reversed-phase chromatography with mesoporphyrin as the internal standard. The Km of coproporphrinogen oxidase is 1.01 +/- 0.23 microM. The activities are 4.07 +/- 0.40 nmol of protoporphyrin IX/h per mg of mitochondrial protein and 224 +/- 19 nmol of protoporphyrin IX/h per g of liver tissue homogenate. The method is sensitive enough for measuring enzyme activity in small amounts of human tissue from needle biopsy.