The enzymic conversion of coproporphyrinogen III into protoporphyrin IX

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Abstract
A reduced form of protoporphyrin IX, probably protoporphyrinogen IX, is formed during the conversion of coproporphyrinogen III into protoporphyrin IX by a mitochondrial extract. In addition to coprogenase this extract appears to contain protoporphyrinogen oxidase. The mitochondrial extract converts coproporphyrinogen III into protoporphyrin IX, coproporphyrinogen IV into an isomer of protoporphyrin as yet undefined, and deuteroporphyrinogen IX-4-propionic acid into 4-mono-vinyldeuteroporphyrin. Coproporphyrinogens I and II, and copropor-phyrins I and III, are inactive. Acid hydrolysis of the protein-bound porphyrins formed during incubation of the mitochondrial extract with coproporphyrinogen HI yielded a tetracarboxylic porphyrin, which appears to be coproporphyrin, and a monovinyl-dicarboxylic porphyrin. Coproporphyrinogen HI is readily oxidized by potassium ferricyanide, but is reasonably stable, at pH 7.4 in the dark, in the presence of FAD, methylene blue, phenazine methosulphate, 2,6-dichlorophenol-indophenol or oxidized cytochrome c. Formation of protoporphyrin IX from coproporphyrinogen HI by an extract of ox-liver mitochondria is an oxygen-dependent process. The maximum rate is observed at oxygen concentrations of 20% (v/v). Under anaerobic conditions oxygen could not be replaced by FAD, methylene blue, phenazine methosulphate, 2,6-dichlorophenolindophenol or oxidized cytochrome c.