Pascutti P G, Ito A S
Instituto de Física, Universidade de São Paulo, Brazil.
J Photochem Photobiol B. 1992 Dec;16(3-4):257-66. doi: 10.1016/1011-1344(92)80014-m.
The photo-induction of free radicals in synthetic L-dihydroxyphenylalanine (L-DOPA) melanin in the presence of bovine serum albumin (BSA) was studied by electron paramagnetic resonance (EPR) spectroscopy. By monitoring the signal intensities and progressive microwave power saturation it was shown that L-DOPA melanin in solution behaves as a single macromolecule, interacting with BSA and molecular oxygen. In the absence of oxygen, the EPR signal of L-DOPA melanin was homogeneously broadened; the magnetic interaction with oxygen induced inhomogeneous broadening. In aqueous solution, the presence of BSA decreased the accessibility of oxygen to paramagnetic centres in the melanin. On UV-visible illumination, the presence of BSA modified the rates of formation and decay of photoinduced free radicals, resulting in a net enhancement of the EPR signal compared with that observed in pure L-DOPA melanin.
利用电子顺磁共振（EPR）光谱研究了在牛血清白蛋白（BSA）存在下，合成的L-二羟基苯丙氨酸（L-DOPA）黑色素中自由基的光诱导作用。通过监测信号强度和连续微波功率饱和情况，结果表明溶液中的L-DOPA黑色素表现为单个大分子，与BSA和分子氧相互作用。在无氧条件下，L-DOPA黑色素的EPR信号均匀展宽；与氧的磁相互作用导致不均匀展宽。在水溶液中，BSA的存在降低了氧与黑色素中顺磁中心的可及性。在紫外-可见光照射下，BSA的存在改变了光诱导自由基的形成和衰减速率，与纯L-DOPA黑色素相比，导致EPR信号净增强。
