Aerobic and Anaerobic Coproporphyrinogenase Activities in Extracts from Saccharomyces cerevisiae

Coproporphyrinogenase was isolated from mitochondrial extracts of Saccharomyces cerevisiae following mechanical disruption. The enzyme was purified 150-fold by a procedure involving ion exchange chromatography and gel filtration. The molecular weight of the enzyme was 75,000 ± 7,500. The purified enzyme catalyzed the conversion of coproporphyrinogen III to protoporphyrinogen IX under both aerobic and anaerobic conditions. In the presence of air, the conversion was not dependent upon the presence of an exogenous hydrogen acceptor or other cofactors. Under anaerobic conditions, however, coproporphyrinogenase had an absolute requirement for divalent metal ion, ATP, and l-methionine. NAD+ or NADP+ was required as an electron acceptor, the latter being more effective. A pH of 7.6 was optimal for both the aerobic and anaerobic reactions. Apparent Km values of 3.2 x 10-5 m and 2.6 x 10-5 m were determined for the aerobic and anaerobic reactions, respectively. In the presence of high salt concentrations, chelating agents, sulfhydryl reactive compounds, or GSSG both the aerobic and anaerobic coproporphyrinogenase activities were inhibited. Anaerobic activity was also inhibited in the presence of 5 mm GSH or l-ethionine, but neither of these compounds affected the aerobic enzyme activity. Both the aerobic and anaerobic coproporphyrinogenase activities were insensitive to FAD, FMN, 2,4-dinitrophenol, and cyanide.