MOLECULAR-CLONING, SEQUENCING, AND FUNCTIONAL EXPRESSION OF A CDNA-ENCODING HUMAN COPROPORPHYRINOGEN OXIDASE

Coproporphyrinogen oxidase (EC 1.3.3.3) catalyzes the sixth step in th e heme biosynthetic pathway, the oxidation of coproporphyrinogen III t o protoporphyrinogen IX. The activity of this enzyme is deficient in t he disease hereditary coproporphyria. The sequence of the cDNA and pre dicted amino acid sequence of the human coproporphyrinogen oxidase are presented. The human protein sequence contains a region completely ho mologous to that we obtained by sequencing an 11-amino acid peptide fr agment from purified murine fiver coproporphyrinogen oxidase. Results of Southern blotting were consistent with the presence of a single hum an coproporphyrinogen oxidase gene, and Northern blotting demonstrated one transcript of similar size in erythroid and nonerythroid cell lin es. Expression of the cDNA coding for the putative mature human coprop orphyrinogen oxidase in Escherichia coli resulted in a 17-fold increas e in coproporphyrinogen activity over endogenous activity.