Schlessinger Daniel I., Rahimi Nader, Schlessinger Joel
Massachusetts General Hospital
Boston University Medical Campus, Boston, MA
Melanin is a natural pigment found in various tissues throughout the body, most notably in the skin, hair, and eyes. Melanin is synthesized in the epidermis by specialized pigment-producing cells called melanocytes through a biochemical pathway that begins with the amino acid tyrosine. Although melanin's primary function is to protect cells from the damaging effects of UV radiation, it also plays essential roles in skin pigmentation, eye and hair color, evolutionary adaptation to sunlight, and aspects of cutaneous immune function. Disruptions in melanin production can lead to conditions such as albinism, characterized by little or no pigment in the skin, hair, and eyes. Oculocutaneous albinism type 1—the most common form—results from mutations in tyrosinase, a copper-dependent enzyme that is crucial for melanin synthesis. Phenylketonuria is another condition that affects pigmentation, a metabolic disorder characterized by elevated levels of phenylalanine due to a deficiency in phenylalanine hydroxylase. High phenylalanine levels competitively inhibit tyrosinase, thereby interfering with the conversion of tyrosine into melanin. As a result, individuals with phenylketonuria often exhibit fair skin, light hair, and blue eyes due to impaired melanin production.
黑色素是一种天然色素，存在于全身各处的各种组织中，最显著的是在皮肤、头发和眼睛中。黑色素由称为黑素细胞的特殊色素生成细胞在表皮中通过一条从氨基酸酪氨酸开始的生化途径合成。虽然黑色素的主要功能是保护细胞免受紫外线辐射的损害作用，但它在皮肤色素沉着、眼睛和头发颜色、对阳光的进化适应以及皮肤免疫功能方面也起着重要作用。黑色素生成的中断会导致诸如白化病等病症，其特征是皮肤、头发和眼睛中色素很少或没有色素。1型眼皮肤白化病——最常见的形式——是由酪氨酸酶突变引起的，酪氨酸酶是一种对黑色素合成至关重要的铜依赖性酶。苯丙酮尿症是另一种影响色素沉着的病症，是一种代谢紊乱，由于苯丙氨酸羟化酶缺乏导致苯丙氨酸水平升高。高苯丙氨酸水平竞争性抑制酪氨酸酶，从而干扰酪氨酸向黑色素的转化。因此，苯丙酮尿症患者由于黑色素生成受损，通常表现为皮肤白皙、头发浅色和眼睛蓝色。
