Oxygen-regulated steps in the Rhodobacter capsulatus tetrapyrrole biosynthetic pathway

Biel, A J

doi:10.1128/jb.174.16.5272-5274.1992

Cited by 21 publications

(17 citation statements)

References 18 publications

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“…While aminolevulinate increased the protoporphyrin IX levels, the levels were still regulated by oxygen. This is consistent with earlier results which suggest that feedback inhibition of aminolevulinate synthase cannot be the sole mechanism by which the common tetrapyrrole pathway is regulated (5).…”

Section: Resultssupporting

confidence: 82%

“…Aminolevulinate synthase activity is the same in cultures grown under high and low oxygen tensions (5,24), although a sixfold increase in enzyme activity has been reported in photosynthetically grown cultures (24). Additionally, it has been demonstrated that protoporphyrin accumulation in a bchH mutant is regulated by oxygen even in the presence of exogenous aminolevulinate, while the presence of exogenous porphobilinogen abolishes oxygen-mediated regulation, indicating that oxygen must regulate some step later in the pathway (5).…”

Section: Discussionmentioning

confidence: 95%

“…Surprisingly, protoporphyrin IX accumulation was still regulated by oxygen. However, when exogenous porphobilinogen, the second intermediate in the pathway, was added to a culture of the bchH mutant, protoporphyrin IX accumulation was no longer regulated by oxygen (5). This observation indicated that the major oxygen-regulated control point in the common tetrapyrrole pathway is not the synthesis of aminolevulinate.…”

mentioning

confidence: 75%

“…The results presented in Table 2 demonstrate that porphobilinogen levels are regulated by oxygen tension. Previous results demonstrated that the major regulatory point for oxygen-mediated control of the common tetrapyrrole pathway was after aminolevulinate formation (5). From this, it would seem most likely that oxygen would control the conversion of aminolevulinate to porphobilinogen.…”

Section: Discussionmentioning

confidence: 99%

“…This theory was tested in R. capsulatus by growing a bchH mutant (AJB456) under high and low oxygen concentrations in the presence of exogenous aminolevulinate (5). Surprisingly, protoporphyrin IX accumulation was still regulated by oxygen.…”

mentioning

confidence: 99%

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Oxygen-Mediated Regulation of Porphobilinogen Formation inRhodobacter capsulatus

et al. 2002

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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.

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Section: Resultssupporting

confidence: 82%