Tief K, Hahne M, Schmidt A, Beermann F
Swiss Institute for Experimental Cancer Research, Epalinges, Switzerland.
Eur J Biochem. 1996 Oct 1;241(1):12-6. doi: 10.1111/j.1432-1033.1996.0012t.x.
Tyrosinase is one of the key enzymes in mammalian melanin synthesis. The pigment is produced in two different cell types: the pigmented epithelial cell of the retina, and the melanocyte, a cell of neural-crest origin. We recently showed that a fusion gene between regulatory sequences of tyrosinase gene (tyr) and the beta-galactosidase gene (lacZ), when introduced into transgenic mice, resulted in embryonic expression in presumptive pigment cells but also in cells populations along the entire neural tube. This expression in the developing brain was striking, and we therefore asked whether this would still be detectable after birth. Transgenic mice carrying the tyr-lacZ fusion gene showed beta-galactosidase expression in adult brain. On Western blots, we detected tyrosinase-specific bands of 65-68 kDa in brain and eye. Using an affinity-purified antibody, we showed that detection of tyrosinase is specific and competed off by the presence of the cognate tyrosinase-derived peptide. However, neither tyrosine hydroxylase nor Dopa oxidase activity were detected in protein extracts of brain. We therefore suggest that tyrosinase is present in brain but either not functional or catalyzing different reactions compared to pigment cells.
酪氨酸酶是哺乳动物黑色素合成中的关键酶之一。黑色素在两种不同的细胞类型中产生：视网膜色素上皮细胞和神经嵴来源的黑素细胞。我们最近发现，将酪氨酸酶基因（tyr）的调控序列与β-半乳糖苷酶基因（lacZ）的融合基因导入转基因小鼠后，在假定的色素细胞中以及沿整个神经管的细胞群体中均有胚胎期表达。这种在发育中的大脑中的表达很显著，因此我们询问出生后是否仍能检测到。携带tyr-lacZ融合基因的转基因小鼠在成年大脑中显示出β-半乳糖苷酶表达。在蛋白质印迹法中，我们在大脑和眼睛中检测到了65 - 68 kDa的酪氨酸酶特异性条带。使用亲和纯化抗体，我们表明酪氨酸酶的检测是特异性的，并且会被同源酪氨酸酶衍生肽的存在所竞争抑制。然而，在大脑的蛋白质提取物中未检测到酪氨酸羟化酶或多巴氧化酶活性。因此，我们认为大脑中存在酪氨酸酶，但与色素细胞相比，它要么没有功能，要么催化不同的反应。
