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Intrigues and intricacies of the biosynthetic pathways for the enzymatic quinocofactors: PQQ, TTQ, CTQ, TPQ, and LTQ.

Author(s): Klinman, Judith P; Bonnot, Florence | Abstract: A primary focus to the variety of biosynthetic pathways for the production of quinocofactors is reviewed. Proteins containing a unique pair of heme iron enzymes are present in the pathways for the production of TTQ and CTQ. A nonheme iron monooxygenase may play a role in PQQ production and copper ions are essential for the production of TPQ and LTQ. In searching for common features among the pathways, in all cases the initial hydroxylation of either a Tyr or Trp appears necessary. By nature of the structure of Trp, a second ring hydroxylation must occur in some manner during the production of TTQ and CTQ. These hydroxylations are followed by the addition of either a hydroxide ion (TPQ) or a second amino acid side chain (PQQ, TTQ, CTQ, and LTQ), to initiate the final segment of cofactor production. The quinone-dependent enzymes are, in fact, more restrictive than flavin-dependent systems, either acting exclusively on primary amine substrates (TTQ, CTQ, TPQ, and LTQ) or a select number of primary alcohols.