Claiborne, A. and I. Fridovich (1979).
Biochemistry 18(11): 2324-2329.
Abstract:
Studies of the optical spectra of the products formed during peroxidn. of o-dianisidine by horseradish peroxidase (HRP) indicate at least 3 distinct species. At pH 3.7 and 4°, peroxidn. of dianisidine at low concns. yields the free dianisidine quinonediimine (the 2-equiv oxidized form) with λmax 452 and 514 nm. At higher concns., the 1st detectable product is not the free quinonediimine but an intermol. complex (meriquinone or charge-transfer complex) consisting of quinonediimine and parental diamine. This complex is freely reversible and is sensitive to simple diln. or acidification, either of which restores the spectrum of the free quinonediimine. Furthermore, at near-neutral pH, the quinonediimine appears to undergo irreversible self-coupling yielding yet a different optical spectrum presumably characteristic of the bisazobiphenyl structure proposed by K. M. Moller and P. Ottolenghi (1966). Butylated hydroxyanisole was shown to react in the presence of peroxidase-H2O2 and dianisidine to yield a spectrum (λmax 575 nm) nearly identical with that obtained when Gibbs' reagent (2,6-dichloroquinone-4-chloroimide) was incubated with butylated hydroxyanisole, thus suggesting that the free quinonediimine itself couples with the phenolic antioxidant. Finally, continuous-flow EPR studies of dianisidine oxidn. both with HRP-H2O2 and with ceric sulfate were unable to detect any free dianisidine semiquinone radical in the steady state; it is concluded that oxidn. of dianisidine occurs in a rapid 2-electron process in both the HRP-H2O2 and Ce(IV) systems
Biochemistry 18(11): 2324-2329.
Abstract:
Studies of the optical spectra of the products formed during peroxidn. of o-dianisidine by horseradish peroxidase (HRP) indicate at least 3 distinct species. At pH 3.7 and 4°, peroxidn. of dianisidine at low concns. yields the free dianisidine quinonediimine (the 2-equiv oxidized form) with λmax 452 and 514 nm. At higher concns., the 1st detectable product is not the free quinonediimine but an intermol. complex (meriquinone or charge-transfer complex) consisting of quinonediimine and parental diamine. This complex is freely reversible and is sensitive to simple diln. or acidification, either of which restores the spectrum of the free quinonediimine. Furthermore, at near-neutral pH, the quinonediimine appears to undergo irreversible self-coupling yielding yet a different optical spectrum presumably characteristic of the bisazobiphenyl structure proposed by K. M. Moller and P. Ottolenghi (1966). Butylated hydroxyanisole was shown to react in the presence of peroxidase-H2O2 and dianisidine to yield a spectrum (λmax 575 nm) nearly identical with that obtained when Gibbs' reagent (2,6-dichloroquinone-4-chloroimide) was incubated with butylated hydroxyanisole, thus suggesting that the free quinonediimine itself couples with the phenolic antioxidant. Finally, continuous-flow EPR studies of dianisidine oxidn. both with HRP-H2O2 and with ceric sulfate were unable to detect any free dianisidine semiquinone radical in the steady state; it is concluded that oxidn. of dianisidine occurs in a rapid 2-electron process in both the HRP-H2O2 and Ce(IV) systems
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