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.
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: k0[PQQ] [NAD(P)H] = k1 [NAD(P)H], where k0[PQQ] = 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.
Sugioka
K
K
College of Medical Care and Technology, Gunma University, Japan.
Nakano
M
M
Naito
I
I
Tero-Kubota
S
S
Ikegami
Y
Y
D003067:Coenzymes; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007700:Kinetics; D009243:NAD; D009249:NADP; D010084:Oxidation-Reduction; D010100:Oxygen; D045542:PQQ Cofactor; D011804:Quinolines
D003067:Coenzymes; D005609:Free Radicals; D011804:Quinolines; D009243:NAD; D009249:NADP; D045542:PQQ Cofactor; D010100:Oxygen