Enzyme - Nicotinate-nucleotide--dimethylbenzimidazole phosphoribosyltransferase

Alternative Name(s)
  • N(1)-alpha-phosphoribosyltransferase.
  • Nicotinate mononucleotide-dimethylbenzimidazole
  • phosphoribosyltransferase.

Catalytic Activity

5,6-dimethylbenzimidazole + nicotinate beta-D-ribonucleotide = alpha-ribazole 5'-phosphate + H(+) + nicotinate


There are no Cofactors for this Enzyme

Reaction Mechanism

    Nicotinate mononucleotide:5,6- dimethylbenzimidazole (DMB) phosphoribosyltransferase (CobT) is crucial in the synthesis of alpha-ribose-5'-phosphate, a precursor to the lower ligand of colbamin. The biosynthesis of colbamin requires more than 25 committed enzymes, and the biosynthetic pathway has received much interest because of its complexity. Colbamin synthesis is also of interest in evolutionary biology because of its utilisation by early forms of bacteria and Archaea.

    The enzyme has also been shown to act on benzimidazole, and the clostridial enzyme acts on adenine to form 7-alpha-D-ribosyladenine 5'-phosphate.

    The carboxylate side chain of Glu317 acts as a catalytic base, abstracting the proton of the N3 of DMB, whereupon the N1 atom attacks the C1' carbon of ribose with concerted displacement of the nicotinate ring. This leads to the direct displacement reaction, with a inversion of configuration of the carbon centre.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Glu Q05603 317 1d0s 317
    Glu Q05603 174 1d0s 174
    Step Components

    overall reactant used, rate-determining step, bimolecular nucleophilic substitution, proton transfer, overall product formed

    Step 1.

    The N1 of dimethylbenzimidazole initiates a nucleophilic attack on the C1 of the nicotinate D-ribonucleotide in a substitution reaction, eliminating nicotinate.


    The products of the reaction.

Reaction Parameters

  • Kinetic Parameters
    Organism KM Value [mM] Substrate Comment
    Salmonella enterica 0.1 beta-nicotinate D-ribonucleotide mutant G257D, at 37°C
    Sporomusa ovata 3.9 5,6-Dimethylbenzimidazole pH 9.0, 37°C, wild-type
  • Temperature

    There are no reaction parameters information for this Enzyme.

  • pH
    Organism pH Range Comment
    Propionibacterium freudenreichii subsp. shermanii 7.3 - 9.7 pH 7.3: about 60% of maximum activity, pH 9.7: about 90% of maximum activity

Associated Proteins

Protein name Organism
Nicotinate-nucleotide--dimethylbenzimidazole phosphoribosyltransferase Salmonella typhimurium (strain LT2 / SGSC1412 / ATCC 700720)
Probable nicotinate-nucleotide--dimethylbenzimidazole phosphoribosyltransferase CobT Mycobacteroides abscessus
Nicotinate-nucleotide-dimethylbenzimidazole phosphoribosyltransferase Photobacterium aphoticum
Nicotinate-nucleotide dimethylbenzimidazole-P phophoribosyl transferase Ralstonia solanacearum
Nicotinate-nucleotide dimethylbenzimidazole-P phophoribosyl transferase (Part 1) Syntrophaceticus schinkii