Separation of amino acid—oxazole derivatives of the redox coenzyme pyrroloquinoline quinone by capillary zone electrophoresis

Abstract Condensation products (oxazole derivatives) from the reaction of the coenzyme pyrroloquinoline quinone (PQQ) with several α-amino acids were successfully separated by capillary zone electrophoresis. Addition of a certain organic solvent such as dimethyl sulphoxide to the electrolyte solution is essential for reproducible and complete separation. The organic modifier appears to prevent the oxazole derivatives from adsorbing on the capillary wall. Product analysis of the condensation reactions of PQQ with amino acids was performed by this method and the mechanism is discussed briefly. PQQ-spiked bovine serum was also analysed. Unsubstituted type 1 oxazole derivative was predominantly detected. This result suggests that most of the PQQ in mammalian fluids, if any, exists as PQQ derivatives, probably as a type 1 oxazole derivative.