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CHEMIEXCITATION IN THE PEROXIDATIVE METABOLISM OF N ‐METHYLCARBAZOLE: MECHANISTIC IMPLICATIONS
Author(s) -
Melo Mariza Pires,
Cilento Giuseppe
Publication year - 1994
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1994.tb09675.x
Subject(s) - chemistry , peroxidase , horseradish peroxidase , excited state , photochemistry , electron transfer , metabolism , lipoxygenase , iminium , enzyme , organic chemistry , biochemistry , catalysis , physics , nuclear physics
The peroxidative metabolism of N ‐methylcarbazole emits light independently of the presence of oxygen. It is likely that two chemiexcited transients are formed by electron transfer to the activated peroxidase, the cation radical by one electron transfer and a cation biradical by two electron transfer consistent with the failure to observe horseradish peroxidase‐II in the steady state of the reaction. In the spectral range investigated (390–700 nm) the observed emission (570–700 nm) is ascribed to the biradical, as the latter is equivalent to an excited state of the postulated iminium cation. While lipoxygenase has no effect upon N ‐methylcarbazole, it markedly enhances the emission if peroxidase is present. This effect requires oxygen and is ascribed to an excited product formed by lipoxygenase acting upon an intermediate hydroperoxide of the aerobic process promoted by peroxidase. Our results are of importance on two counts. First they extend to N ‐rnethylcarbazole the formation of excited species in the peroxidative metabolism of important xenobiotics. Second, the mechanistic information they provide supports the scheme of metabolism postulated by Kedderis et al. (1986, J. Biol. Chem. 261, 15910–15914).