King M M, Lai E K, McCay P B
J Biol Chem. 1975 Aug 25;250(16):6496-502.
Evidence for the formation of singlet oxygen during the oxidation of NADPH by liver microsomes is presented. The evidence is based primarily on the enzyme-dependent formation of dibenzoylethylene from diphenylfuran, a reaction which is specific for singlet oxygen. The apparent formation of singlet oxygen is coupled to the occurrence of peroxidation of microsomal lipid, a phenomenon known to be associated with NADPH oxidation by the particles. Both the peroxidation of lipid and the apparent formation of singlet oxygen are related to the amount of Fe3+ present in the system and the results are consistent with the possibility that the singlet oxygen formed by this system is derived from the breakdown of lipid peroxides. If 1O2 is formed from breakdown of lipid peroxides, it would be dependent on O-/-2 formation because superoxide anion has been shown to undergo reactions in this system which generate extremely reactive free radicals (probably hydroxyl) that initiate lipid peroxidation. These peroxides are quite unstable and their degradation may be the source of 1O2. We have consistently observed that O-/-2 itself is not a reactive radical with respect to lipids or radical scavengers. Hence, O-/-2 cannot be the radical which initiates lipid peroxidation on which 1O2 generation appears to depend. The results may offer at least part of the explanation for the dietary requirement for alpha-tocopherol which not only scavenges free radicals but quenches singlet oxygen as well. This report also includes description of studies indicating that another enzyme, xanthine oxidase, which forms superoxide anion during its activity under aerobic conditions, does not form singlet oxygen during its function. This finding is in contrast to reports of others which indicate that xanthine oxidase activity does produce 1O2.
本文提供了肝脏微粒体氧化NADPH过程中形成单线态氧的证据。该证据主要基于从二苯基呋喃酶依赖性形成二苯甲酰乙烯，此反应对单线态氧具有特异性。单线态氧的明显形成与微粒体脂质过氧化的发生相关，脂质过氧化是一种已知与微粒体氧化NADPH有关的现象。脂质过氧化和单线态氧的明显形成均与系统中存在的Fe3+量有关，结果与该系统形成的单线态氧源自脂质过氧化物分解的可能性一致。如果单线态氧由脂质过氧化物分解形成，它将依赖于超氧阴离子的形成，因为已表明超氧阴离子在此系统中会发生反应，产生引发脂质过氧化的极具反应性的自由基（可能是羟基自由基）。这些过氧化物非常不稳定，其降解可能是单线态氧的来源。我们一直观察到，超氧阴离子本身对于脂质或自由基清除剂而言并非反应性自由基。因此，超氧阴离子不可能是引发脂质过氧化的自由基，而单线态氧的产生似乎依赖于脂质过氧化。这些结果可能至少部分解释了对α-生育酚的饮食需求，α-生育酚不仅能清除自由基，还能淬灭单线态氧。本报告还包括对研究的描述，这些研究表明另一种酶——黄嘌呤氧化酶，在有氧条件下其活性过程中会形成超氧阴离子，但在其功能过程中不会形成单线态氧。这一发现与其他一些报告相反，那些报告表明黄嘌呤氧化酶活性确实会产生单线态氧。
