Evidence for an Atypical Tetrapyrrole Biosynthetic Pathway inDesulfovibrio: Back Conversion of Sirohydrochlorin into Porphyrins

Isotope labeling experiments performed onDesulfovibrio vulgarishave determined that two methyl groups of heme c and its precursors coprophyrin III and protoporphyrin IX come from theS-methyl group of methionine and not from the expected source which would be C2 of 5-aminolevulinic acid.In vitrobiosynthetic experiments with broken-cell extracts led to the isolation of small quantities of novel new tetrapyrrole intermediates which could be structurally identified by visible spectroscopy and mass spectrometry. These intermediates suggest that sirohydrochlorin is decarboxylated at pyrrole rings C and D and deacteylated at rings A and B to produce coproporphyrin.