Ito A S, Azzellini G C, Silva S C, Serra O, Szabo A G
Instituto de Física, Universidade de São Paulo, Brasil.
Biophys Chem. 1992 Nov;45(1):79-89. doi: 10.1016/0301-4622(92)87025-e.
Optical absorption and fluorescence spectroscopies were employed in the study of the interaction between synthetic L-dopa (dihydroxyphenylalanine) melanin and the cationic porphyrins tetrakis(4-N-methylpyridyl) porphyrin (TMPyP), tetrakis(4-N-benzylpyridyl)porphyrin (TBzPyP), zinc tetrakis(4-N-methylpyridyl)porphyrin (ZnTMPyP) and zinc tetrakis (4-N-benzylpyridyl)porphyrin (ZnTBzPyP). Optical absorption and fluorescence properties of the porphyrins were dependent on the symmetry of the central ring. No evidence was found for dimerization of the porphyrins in phosphate buffer, pH 7, in the concentration range between 4 x 10(-8) to 5 x 10(-5) M. Addition of L-dopa melanin red shifted the optical absorption spectra of porphyrins, concomitant to broadening and reduction in intensity of the bands. L-Dopa melanin also strongly quenched the fluorescence of the porphyrins. Time resolution of the fluorescence decay of porphyrins showed at least two lifetimes that were only slightly modified in the presence of melanin. The interaction between melanin and porphyrin resulted in the formation of non-fluorescent ground state complexes. It was found that there are two different classes of binding sites in melanin for complexation with cationic porphyrins and the values of dissociation constants are of the order of 10(-8) M. These values and the number of binding sites are dependent on the nature of the porphyrins. It was shown that the binding has electrostatic origin, but it is also affected by metal coordination and hydrophobic interaction.
采用光吸收光谱和荧光光谱研究了合成的L-多巴（二羟基苯丙氨酸）黑色素与阳离子卟啉四（4-N-甲基吡啶基）卟啉（TMPyP）、四（4-N-苄基吡啶基）卟啉（TBzPyP）、四（4-N-甲基吡啶基）锌卟啉（ZnTMPyP）和四（4-N-苄基吡啶基）锌卟啉（ZnTBzPyP）之间的相互作用。卟啉的光吸收和荧光性质取决于中心环的对称性。在pH 7的磷酸盐缓冲液中，浓度范围为4×10⁻⁸至5×10⁻⁵ M时，未发现卟啉二聚化的证据。添加L-多巴黑色素使卟啉的光吸收光谱发生红移，同时谱带变宽且强度降低。L-多巴黑色素也强烈猝灭了卟啉的荧光。卟啉荧光衰减的时间分辨显示至少有两个寿命，在黑色素存在下仅略有改变。黑色素与卟啉之间的相互作用导致形成非荧光基态复合物。发现黑色素中有两类不同的结合位点可与阳离子卟啉络合，解离常数的值约为10⁻⁸ M。这些值和结合位点的数量取决于卟啉的性质。结果表明，这种结合具有静电起源，但也受金属配位和疏水相互作用的影响。
