Availability of porphobilinogen controls appearance of porphobilinogen deaminase activity in Escherichia coli K-12.

A hemin-permeable hemB mutant had no 5-aminolevulinate dehydratase (ALA D) and extremely low porphobilinogen deaminase (PBG D) activity. When the structural gene for hemB was introduced into this strain on a single-copy plasmid, both activities were observed. When the mutant was grown on PBG, normal PBG D activity was observed. Moreover, a hemA mutant had little or no PBG D activity unless it was grown on ALA or PBG. Neither hemin nor PBG affected the level of PBG D protein produced from in vitro transcription and translation of a plasmid harboring the hemC gene as an insert. We conclude that, in Escherichia coli, PBG availability controls the activity of PBG D at some posttranscriptional level.