Menter J M, Willis I
Department of Medicine, Morehouse School of Medicine, Atlanta, GA 30310-1495, USA.
Pigment Cell Res. 1997 Aug;10(4):214-7. doi: 10.1111/j.1600-0749.1997.tb00487.x.
The polyquinoid nature of eumelanin(s) enables them to couple oxidation of electron donors with the reduction of electron acceptors. We have studied the ability of synthetic (Sigma) and "biological" (cuttlefish sepia) melanins to mediate electron transfer between hydroxybenzene donors (tyrosine, dopa, chemical depigmenters) and model acceptors (ferricyanide, tyrosinase). 1) Depending on the reductant, melanin either retards or accelerates ferricyanide reduction. Reaction kinetics are consistent with a mechanism involving non-interactive binding of both hydroxybenzene and ferricyanide to melanin prior to coupled electron transfer. 2) Melanins also act as an electron conduit in markedly accelerating the tyrosinase-catalyzed oxygenation of p-hydroxyanisole (MMEH). The active species appears to be a complex between melanin and MMEH. The magnitude of both effects depend on the type of melanin as well as its oxidation state. Sepia (eu)melanin appears to protect against UV-induced damage to acid-soluble collagen, as judged by irreversible loss of intrinsic collagen fluorescence. Photoprotection against this type of damage appears primarily to involve optical absorption/scattering by the pigment.
真黑素的聚醌性质使其能够将电子供体的氧化与电子受体的还原偶联起来。我们研究了合成（西格玛）和“生物”（乌贼墨汁）黑素介导羟基苯供体（酪氨酸、多巴、化学脱色剂）与模型受体（铁氰化物、酪氨酸酶）之间电子转移的能力。1）根据还原剂的不同，黑素要么延缓要么加速铁氰化物的还原。反应动力学与一种机制相符，该机制涉及在偶联电子转移之前，羟基苯和铁氰化物与黑素的非相互作用结合。2）黑素还作为电子传导途径，显著加速酪氨酸酶催化的对甲氧基苯酚（MMEH）的氧化。活性物种似乎是黑素与MMEH之间的复合物。这两种效应的大小取决于黑素的类型及其氧化态。从酸性可溶胶原蛋白固有荧光的不可逆损失判断，乌贼墨汁（真）黑素似乎能防止紫外线诱导的损伤。针对此类损伤的光保护作用似乎主要涉及色素的光吸收/散射。
