Kinetic Study of the Quenching Reaction of Singlet Oxygen by Pyrroloquinolinequinol (PQQH2, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

摘要

A kinetic study of the quenching reaction of singlet oxygen (~1O2) with pyrroloquinolinequinol (PQQH2, a reduced form of pyrroloquinolinequinone (PQQ)), PQQNa2 (disodium salt of PQQ), and seven kinds of natural antioxidants (vitamin C (Vit C), uric acid (UA), epicatechin (EC), epigallocatechin (EGC), α-tocopherol (α-Toc), ubiquinol-10 (UQ_(10)H2), and β-carotene (β-Car)) has been performed. The second-order rate constants k_Q(k_Q= k_q + K_r> physical quenching and chemical reaction) for the reaction of ~1O2 with PQQH2> PQQNa2, and seven kinds of antioxidants were measured in 5.0 wt % Triton X-100 micellar solution (pH 7.4), using UV-visible spectrophotometry. The k_Q values decreased in the order of β-Car > PQQH2 > α-Toc > UA > UQ_(10)H2 > Vit C ~ EGC > EC PQ.QNa2. PQQH2 is a water-soluble antioxidant. The singlet oxygen-quenching activity of PQQH2 was found to be 6.3, 2.2, 6.1, and 22 times as large as the corresponding those of water-soluble antioxidants (Vit C, UA, EGC, and EC). Further, the activity of PQQH2 was found to be 2.2 and 3.1 times as large as the corresponding activity of lipid-soluble antioxidants (a-Toc and UQ_(10)H2). On the other hand, the activity of PQQH2 is 6.4 times as small as that of β-Car. It was observed that the chemical reaction (k_r) is almost negligible in the quenching reaction of ~1O2 by PQQH2. The result suggests that PQQH2 may contribute to the protection of oxidative damage in biological systems, by quenching ~1O2.