The cobinamide amidohydrolase (cobyric acid-forming) CbiZ enzyme: a critical activity of the cobamide remodelling system of Rhodobacter sphaeroides

Mol Microbiol. 2009 Dec;74(5):1198-210. doi: 10.1111/j.1365-2958.2009.06928.x. Epub 2009 Nov 2.


The chemical structures of cobamides [cobalamin (Cbl)-like compounds] are the same, except for the lower ligand, which in adenosylcobalamin (AdoCbl) is 5,6-dimethylbenzimidazole, and in adenosylpseudocobalamin (AdopseudoCbl) is adenine. Why the lower ligand of cobamides varies and what the mechanism of lower ligand replacement is are long-standing questions in the field of B(12) biosynthesis. Work reported here uncovers the strategy used by the photosynthetic alpha-proteobacterium Rhodobacter sphaeroides to procure the cobamide it needs to grow on acetate as a carbon and energy source. On the basis of genetic and biochemical evidence we conclude that, in R. sphaeroides, the activity of the cobyric acid-producing amidohydrolase CbiZ enzyme is essential for the conversion of AdopseudoCbl into AdoCbl, the cobamide needed for the catabolism of acetate. The CbiZ enzyme uses AdopseudoCbl as a substrate, but not AdoCbl. Implications of these findings for cobamide remodelling in R. sphaeroides and in other CbiZ-containing microorganisms are discussed.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amidohydrolases / genetics
  • Amidohydrolases / metabolism*
  • Benzimidazoles / metabolism
  • Cobamides / chemistry
  • Cobamides / metabolism*
  • Rhodobacter sphaeroides / enzymology*
  • Rhodobacter sphaeroides / genetics
  • Rhodobacter sphaeroides / metabolism


  • Benzimidazoles
  • Cobamides
  • 5,6-dimethylbenzimidazole
  • Amidohydrolases