Properties of a coenzyme, pyrroloquinoline quinone: generation of an active oxygen species during a reduction-oxidation cycle in the presence of NAD(P)H and O2 |
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| Authors: | K Sugioka M Nakano I Naito S Tero-Kubota Y Ikegami |
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| Institution: | College of Medical Care and Technology, Gunma University, Japan. |
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| Abstract: | The oxidation of NAD(P)H by pyrroloquinoline quinone (PQQ) was non-enzymatically carried out at physiological pH in the presence of O2. The PQQ-NAD(P)H system requires about 1 mol of O2 for the oxidation of 1 mol of NAD(P)H. The oxidation of NAD(P)H occurred at a pseudo-first-order rate with respect to NAD(P)H and was of zero order with respect to PQQ concentration in in the presence of O2: k0PQQ] NAD(P)H] = k1 NAD(P)H], where k0PQQ] = k1, in which PQQ] represents the initial concentration of PQQ. k0 values for NADH and NADPH were 3.4.10(2) M-1.min-1 and 2.0.10(2) M-1.min-1, respectively, at 25 degrees C and at 258 microM O2 (initial concentration). The system produced O-2, probably by the interaction of PQQ.H and/or NAD(P).with O2, during the oxidation of NAD(P)H. PQQH2 and PQQ.H were easily oxidized to PQQ in the presence of O2, yielding H2O2. |
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