Kinetic analysis of oxazolopyrroloquinoline formation in the reaction of coenzyme PQQ with amino acids by capillary zone electrophoresis

Kinetics of the formation of oxazolopyrroloquinoline (OPQ) derivatives from coenzyme pyrroloquinoline quinone (PQQ) and three α-amino acids (glycine, serine and valine) was studied with the aid of capillary zone electrophoresis. Glycine and valine were, respectively, converted exclusively into the unsubstituted OPQ (OPQ1) and an OPQ with the valinyl residue (Val-OPQ2), while serine gave OPQ1 and Ser-OPQ2 under basic and acidic conditions, respectively. The OPQ formation exhibited a first-order dependence on each of PQQ and the amino acids. The OPQ1 generation from glycine is 45 times faster than that of Val-OPQ2 at pH 7.4. This result is in accord with an observation that PQQ spiked in bovine serum was converted predominantly into OPQ1. The mechanism of the OPQ formation is discussed in detail.