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Journal of Bacteriology, March 2002, p. 1685-1692, Vol. 184, No. 6
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.6.1685-1692.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Oxygen-Mediated Regulation of Porphobilinogen Formation in Rhodobacter capsulatus

Alan J. Biel,* Keith Canada,,{dagger} David Huang, Karl Indest,,{ddagger} and Karen Sullivan

Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803

Received 16 October 2001/ Accepted 5 December 2001

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 [14C]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.

* Corresponding author. Mailing address: Department of Biological Sciences, Louisiana State University, Rm. 202 Life Sciences Building, Baton Rouge, LA 70803. Phone: (225) 578-2791. Fax: (225) 578-2597. E-mail: abiel1{at}lsu.edu.

{dagger} Present address: Protein Sciences Corporation, Meriden, CT 06450.

{ddagger} Present address: U.S. Army Engineer Research and Development Center, Vicksburg, MS 39180

Journal of Bacteriology, March 2002, p. 1685-1692, Vol. 184, No. 6
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.6.1685-1692.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.





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