The Tetrapyrrole Biosynthetic Pathway and Its Regulation in Rhodobacter capsulatus

  • Sébastien Zappa
  • Keran Li
  • Carl E. Bauer
Conference paper
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 675)


The purple anoxygenic photosynthetic bacterium Rhodobacter capsulatus is capable of growing in aerobic or anaerobic conditions, in the dark or using light, etc. Achieving versatile metabolic adaptations from respiration to photosynthesis requires the use of tetrapyrroles such as heme and bacteriochlorophyll, in order to carry oxygen, to transfer electrons, and to harvest light energy. A third tetrapyrrole, cobalamin (vitamin B12), is synthesized and used as a cofactor for many enzymes. Heme, bacteriochlorophyll, and vitamin B12 constitute three major end products of the tetrapyrrole biosynthetic pathway in purple bacteria. Their respective synthesis involves a plethora of enzymes, several that have been characterized and several that are uncharacterized, as described in this review. To respond to changes in metabolic requirements, the pathway undergoes complex regulation to direct the flow of tetrapyrrole intermediates into a specific branch(s) at the expense of other branches of the pathway. Transcriptional regulation of the tetrapyrrole synthesizing enzymes by redox conditions and pathway intermediates is reviewed. In addition, we discuss the involvement of several transcription factors (RegA, CrtJ, FnrL, AerR, HbrL, Irr) as well as the role of riboswitches. Finally, the interdependence of the tetrapyrrole branches on each other synthesis is discussed.


Heme Synthesis Rhodobacter Capsulatus Ring Contraction Corrin Ring Cobalamin Biosynthesis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Authors and Affiliations

  1. 1.Biology DepartmentIndiana UniversityBloomingtonUSA

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