Oxygen-mediated regulation of porphobilinogen formation in Rhodobacter capsulatus.
A Rhodobacter capsulatus hemC mutant has been isolated and used to show that oxygen regulates the intracellular levels of porphobilinogen. Experiments using a hemB-cat gene fusion demonstrated that oxygen does not transcriptionally regulate hemB transcription. Porphobilinogen synthase activity is not regulated by oxygen nor is the enzyme feedback inhibited by hemin or protoporphyrin IX. It was demonstrated that less than 20% of [(14)C]aminolevulinate was incorporated into bacteriochlorophyll, suggesting that the majority of the aminolevulinate is diverted from the common tetrapyrrole pathway. Porphobilinogen oxygenase activity was not observed in this organism; however, an NADPH-linked aminolevulinate dehydrogenase activity was demonstrated. The specific activity of this enzyme increased with increasing oxygen tension. The results presented here suggest that carbon flow over the common tetrapyrrole pathway is regulated by a combination of feedback inhibition of aminolevulinate synthase and diversion of aminolevulinate from the pathway by aminolevulinate dehydrogenase.
Biel
Alan J
AJ
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA. abiel1@lsu.edu
Canada
Keith
K
Huang
David
D
Indest
Karl
K
Sullivan
Karen
K
D000622:Aminolevulinic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D001429:Bacteriochlorophylls / Q000378:metabolism; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D006427:Hemin / Q000494:pharmacology; D011163:Hydroxymethylbilane Synthase; D006899:Mixed Function Oxygenases / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010100:Oxygen / Q000494:pharmacology*; D011162:Porphobilinogen / Q000378:metabolism*; D000623:Porphobilinogen Synthase / Q000378:metabolism; D011524:Protoporphyrins / Q000494:pharmacology; D016354:Rhodobacter capsulatus / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D029968:Escherichia coli Proteins; D011524:Protoporphyrins; D006427:Hemin; D011162:Porphobilinogen; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; D006899:Mixed Function Oxygenases; C022429:porphobilinogen oxygenase; D011163:Hydroxymethylbilane Synthase; C073160:hemC protein, E coli; D000623:Porphobilinogen Synthase; D010100:Oxygen