Cilento G, Nascimento A L
Department of Biochemistry, Universidade de São Paulo, Brazil.
Toxicol Lett. 1993 Apr;67(1-3):17-28. doi: 10.1016/0378-4274(93)90043-w.
Selected enzymatic systems can efficiently produce a product in the electronically excited triplet state. Earlier, only the formation of electronically excited singlet species was known. The formation of triplet species has been demonstrated with both normal substrates/metabolites and with xenobiotics, even at the cellular level. Triplet excited species have intrinsically much longer lifetimes than excited singlets, whereby they can be potentially important agents for normal and/or deleterious processes, including mutagenesis. Enzymically generated triplet species can damage DNA, even when protein coated, as in the case of the lambda-phage of Escherichia coli. Some evidence of damage by triplet species has also been reported for intact cells. Triplet excited species may produce their effects through type I and/or type II dark photosensitization, that is, the events may be started by H abstraction and/or singlet oxygen/superoxide ion production. The induction of lipid peroxidation, with concomitant clastogenic effects, appears to be of special importance.
特定的酶系统能够高效地产生处于电子激发三重态的产物。此前，人们只知道电子激发单重态物种的形成。三重态物种的形成已在正常底物/代谢物以及异源生物中得到证实，甚至在细胞水平也是如此。三重态激发物种的固有寿命比激发单重态长得多，因此它们可能是正常和/或有害过程（包括诱变）的重要介质。酶促产生的三重态物种即使在有蛋白质包裹的情况下（如大肠杆菌的λ噬菌体）也能损伤DNA。完整细胞中也有一些关于三重态物种造成损伤的证据。三重态激发物种可能通过I型和/或II型暗光敏化产生其效应，也就是说，这些事件可能由氢原子夺取和/或单线态氧/超氧离子的产生引发。脂质过氧化的诱导以及随之而来的致断裂效应似乎尤为重要。
