title: The catalysis of redox cycling by pyrroloquinoline quinone (PQQ), PQQ derivatives, and isomers and the specificity of inhibitors.
abstract: Pyrroloquinoline quinone (PQQ) is a widely distributed redox-active cofactor and essential nutrient. For its detection in protein-free ultrafiltrates or dialysates, a highly sensitive amplification assay was developed on the basis of PQQ's ability to catalyze redox cycling at pH 10 in the presence of excess glycine, oxygen, and nitro blue tetrazolium. Herein, we examine the propensities of PQQ, PQQ triester, and its various isomers, and certain PQQ triester derivatives, to catalyze glycine-fueled redox cycling and show that PQQ is the most capable of catalyzing redox cycling. Furthermore, PQQ has a unique pattern of inhibition induced by a series of PQQ antagonists of different potencies. The data indicate that putative PQQ from a biological sample, separated by HPLC and detected by the glycine-fueled redox-cycling assay, can be further identified as PQQ based on the profile of inhibition it displays with the antagonists such as those employed in this study. The methodology presented here should facilitate the specific detection of PQQ in biological samples.
authors.affiliation: Laboratory of Human Biochemistry, Children's Hospital and Harvard Schools of Medicine and Dental Medicine, Boston, Massachusetts, 02115, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Paz
authors.forename: P
authors.initials: P
authors.lastname: Martin
authors.forename: R
authors.initials: R
authors.lastname: Flückiger
authors.forename: J
authors.initials: J
authors.lastname: Mah
authors.forename: P M
authors.initials: PM
authors.lastname: Gallop
mesh_terms: D000818:Animals; D002384:Catalysis; D003067:Coenzymes / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D066298:In Vitro Techniques; D007536:Isomerism; D010084:Oxidation-Reduction; D045542:PQQ Cofactor; D015363:Quinolones / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000302:isolation & purification; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D003067:Coenzymes; D015363:Quinolones; D045542:PQQ Cofactor