Accumulation of porphobilinogen and other pyrroles by mutant and wild type Rhodopseudomonas spheroides: Regulation by heme

Abstract

Certain mutant strains of Rhodopseudomonas spheroides accumulate coproporphyrin(ogen) and porphobilinogen when incubated with low aeration in malate-glutamate medium supplemented with glycine and succinate. Strains 6-6 and 6-6R have barely detectable levels of uroporphyrinogen synthetase and accumulate porphobilinogen. Strain 6-6R is more active than 6-6 in porphobilinogen formation but is less active in heme synthesis. Production of porphobilinogen by strain 6-6 is stimulated by addition of δ-aminolevulinate or o-phenanthroline but neither additive affects strain 6-6R. Strain 2–33 accumulates porphobilinogen and coproporphyrin(ogen) and is exceptionally low in heme synthesis. Inhibition of bacteriochlorophyll synthesis by puromycin in the wild type and strain 6-6R is accompanied by an acceleration in heme synthesis. The wild type accumulates coproporphyrin(ogen) upon addition of o-phenanthroline but this is prevented by the prior addition of puromycin. It is concluded that the excess production of pyrroles by the mutants and by the wild type in response to o-phenanthroline is attributable to failure of feedback control of δ-aminolevulinate synthetase by heme. The mutants are convenient sources of porphobilinogen and coproporphyrin.