Levine M
J Biol Chem. 1986 Jun 5;261(16):7347-56.
Ascorbic acid enhancement of norepinephrine formation from tyrosine in cultured bovine chromaffin cells was characterized in detail as a model system for determining ascorbate requirements. In resting cells, ascorbic acid increased dopamine beta-monooxygenase activity without changing tyrosine 3-monooxygenase activity. [14C]Norepinephrine specific activity was increased by ascorbic acid, while [14C]dopamine specific activity was unchanged. Dopamine content, dopamine biosynthesis, tyrosine content, and tyrosine uptake were also unaffected by ascorbic acid. Furthermore, increased norepinephrine formation could not be attributed to changes in norepinephrine catabolism. Enhancement of dopamine beta-monooxygenase activity was specific for ascorbic acid, since other reducing agents with higher redox potentials were unable to increase norepinephrine formation. The specific effect of ascorbic acid on enhancement of norepinephrine formation was also observed in chromaffin cells stimulated to secrete with carbachol, acetylcholine, veratridine, and potassium chloride. In stimulated cells with and without ascorbate, there were no differences in dopamine content, tyrosine uptake, dopamine specific activity, and norepinephrine catabolism. These data indicate that, under a wide variety of conditions, only one catecholamine biosynthetic enzyme activity, dopamine beta-monooxygenase, is specifically stimulated by ascorbic acid alone in cultured chromaffin cells. This model system exemplifies a new approach for determining ascorbic acid requirements in cells and animals.
在培养的牛嗜铬细胞中，以酪氨酸生成去甲肾上腺素过程中抗坏血酸的增强作用作为确定细胞抗坏血酸需求的模型系统进行了详细表征。在静息细胞中，抗坏血酸增加了多巴胺β-单加氧酶活性，而酪氨酸3-单加氧酶活性未改变。抗坏血酸增加了[14C]去甲肾上腺素的比活性，而[14C]多巴胺的比活性未变。多巴胺含量、多巴胺生物合成、酪氨酸含量和酪氨酸摄取也不受抗坏血酸影响。此外，去甲肾上腺素生成的增加不能归因于去甲肾上腺素分解代谢的变化。多巴胺β-单加氧酶活性的增强对抗坏血酸具有特异性，因为其他具有更高氧化还原电位的还原剂无法增加去甲肾上腺素的生成。在用卡巴胆碱、乙酰胆碱、藜芦碱和氯化钾刺激分泌的嗜铬细胞中也观察到了抗坏血酸对去甲肾上腺素生成增强的特异性作用。在有和没有抗坏血酸的刺激细胞中，多巴胺含量、酪氨酸摄取、多巴胺比活性和去甲肾上腺素分解代谢没有差异。这些数据表明，在多种条件下，在培养的嗜铬细胞中，仅有一种儿茶酚胺生物合成酶活性，即多巴胺β-单加氧酶，受到抗坏血酸的特异性刺激。该模型系统例证了一种确定细胞和动物抗坏血酸需求的新方法。
