Abou-Donia M M, Wilson S P, Zimmerman T P, Nichol C A, Viveros O H
J Neurochem. 1986 Apr;46(4):1190-9. doi: 10.1111/j.1471-4159.1986.tb00637.x.
Selective modification of the tetrahydrobiopterin levels in cultured chromaffin cells were followed by changes in the rate of tyrosine hydroxylation. Addition of sepiapterin, an intermediate on the salvage pathway for tetrahydrobiopterin synthesis, rapidly increased intracellular levels of tetrahydrobiopterin and elevated the rate of tyrosine hydroxylation in the intact cell. Tyrosine hydroxylation was also enhanced when tetrahydrobiopterin was directly added to the incubation medium of intact cells. When the cultured chromaffin cells were treated for 72 h with N-acetylserotonin, an inhibitor of sepiapterin reductase, tetrahydrobiopterin content and the rate of tyrosine hydroxylation were decreased. Addition of sepiapterin or N-acetylserotonin had no consistent effect on total extractable tyrosine hydroxylase activity or on catecholamine content in the cultured chromaffin cells. Three-day treatment of chromaffin cell cultures with compounds that increase levels of cyclic AMP (forskolin, cholera toxin, theophylline, dibutyryl- and 8-bromo cyclic AMP) increased total extractable tyrosine hydroxylase activity and GTP-cyclohydrolase, the rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin. Tetrahydrobiopterin levels and intact cell tyrosine hydroxylation were markedly increased after 8-bromo cyclic AMP. The increase in GTP-cyclohydrolase and tetrahydrobiopterin induced by 8-bromo cyclic AMP was blocked by the protein synthesis inhibitor cycloheximide. Agents that deplete cellular catecholamines (reserpine, tetrabenazine, and brocresine) increased both total tyrosine hydroxylase and GTP-cyclohydrolase activities, although treating the cultures with reserpine or tetrabenazine resulted in no change in cellular levels of cyclic AMP. Brocresine and tetrabenazine increased tetrahydrobiopterin levels, but the addition of reserpine to the cultures decreased catecholamine and tetrahydrobiopterin content and resulted in a decreased rate of intact cell tyrosine hydroxylation in spite of the increased activity of the total extractable enzyme. These data indicate that in cultured chromaffin cells GTP-cyclohydrolase activity like tyrosine hydroxylase activity is regulated by both cyclic AMP-dependent and cyclic AMP-independent mechanisms and that the intracellular level of tetrahydrobiopterin is one of the many factors that control the rate of tyrosine hydroxylation.
培养的嗜铬细胞中四氢生物蝶呤水平的选择性改变伴随着酪氨酸羟化速率的变化。添加蝶酰三谷氨酸，四氢生物蝶呤合成补救途径中的一种中间体，可迅速提高细胞内四氢生物蝶呤水平，并提高完整细胞中酪氨酸羟化的速率。当将四氢生物蝶呤直接添加到完整细胞的孵育培养基中时，酪氨酸羟化也会增强。当培养的嗜铬细胞用蝶酰三谷氨酸还原酶抑制剂N-乙酰血清素处理72小时后，四氢生物蝶呤含量和酪氨酸羟化速率降低。添加蝶酰三谷氨酸或N-乙酰血清素对培养的嗜铬细胞中总可提取酪氨酸羟化酶活性或儿茶酚胺含量没有一致的影响。用增加环磷酸腺苷水平的化合物（福斯可林、霍乱毒素、茶碱、二丁酰环磷腺苷和8-溴环磷腺苷）对嗜铬细胞培养物进行三天处理，可增加总可提取酪氨酸羟化酶活性和鸟苷三磷酸环化水解酶，后者是四氢生物蝶呤生物合成中的限速酶。8-溴环磷腺苷处理后，四氢生物蝶呤水平和完整细胞酪氨酸羟化明显增加。8-溴环磷腺苷诱导的鸟苷三磷酸环化水解酶和四氢生物蝶呤的增加被蛋白质合成抑制剂环己酰亚胺阻断。消耗细胞儿茶酚胺的药物（利血平、丁苯那嗪和布罗克辛）增加了总酪氨酸羟化酶和鸟苷三磷酸环化水解酶的活性，尽管用利血平或丁苯那嗪处理培养物后细胞内环磷酸腺苷水平没有变化。布罗克辛和丁苯那嗪增加了四氢生物蝶呤水平，但向培养物中添加利血平会降低儿茶酚胺和四氢生物蝶呤含量，并导致完整细胞酪氨酸羟化速率降低，尽管总可提取酶的活性增加了。这些数据表明，在培养的嗜铬细胞中，鸟苷三磷酸环化水解酶活性与酪氨酸羟化酶活性一样，受环磷酸腺苷依赖性和环磷酸腺苷非依赖性机制的调节，并且细胞内四氢生物蝶呤水平是控制酪氨酸羟化速率的众多因素之一。
