Unexplored interactions between pyrroloquinoline quinone and beta-nicotinamide adenine dinucleotide

摘要

The interactions between pyrroloquinoline quinone (PQQ) and beta-nicotinamide adenine dinucleotide (NAD(H)) characterized by spectral and voltammetric means are reported in this paper. PQQ exists with six major acid-base derivatives in aqueous solutions; the derivative predominating at pH 3, denoted H(2)Q(-), was characterized to be responsible for the electrochemical and photochemical activities of PQQ, such as for the photooxidation of NADH. In contrast, the derivatives predominating at pH > 5, such as HQ(2-) and Q(3-), are responsible for the interaction with NAD(+); the equilibrium constant was estimated to be similar to 10(6). Although the basic derivatives are less active in emission compared to H(2)Q(-), incorporating NAD(+) can enhance their activity in this respect. The titrations of NAD(+) with HQ(2-) and Q(3-) confirm the complexation reactivity of PQQ to NAD(+), and suggest that the reaction sites of PQQ for NAD(+) are the same as for Ca2+ ions. Thanks to those unique properties, PQQ can photochemically sense glucose and ethanol as NAD(+) and the respective dehydrogenases are incorporated. (C) 2007 Elsevier B.V. All rights reserved.