Induction of delta-Aminolevulinic Acid Synthase Activity and Inhibition of Heme Synthesis in Euglena gracilis by N-Methyl Mesoporphyrin IX

N-Methyl mesoporphyrin IX, an inhibitor of heme synthesis, increases extractable δ-aminolevulinic acid (ALA) synthase activity when administered to growing cultures of Euglena gracilis Klebs strain Z Pringsheim in micromolar concentrations. Wild-type light-grown green cells and white aplastidic cells exhibited 2.8-fold and 1.8-fold increases, respectively, in ALA synthase activity within five to six hours after incubation with 4 × 10⁻⁶ molar N-methyl mesoporphyrin IX. Protoheme levels were decreased and ⁵⁹Fe incorporation into heme was inhibited by N-methyl mesoporphyrin IX, indicating that, as in animal cells, N-methyl mesoporphyrin IX acts specifically to block iron insertion into protoporphyrin IX. Chlorophyll synthesis in wild-type cells was not affected within the first 6 hours after administration of N-methyl mesoporphyrin IX.