Ribeiro P, Kaufman S
Laboratory of Neurochemistry, National Institute of Mental Health, Bethesda, Maryland 20892.
Neurochem Res. 1994 May;19(5):541-8. doi: 10.1007/BF00971328.
Tetrahydrobiopterin (BH4), the obligatory cofactor of the aromatic amino acid hydroxylases, decreased the in situ 32P-phosphorylation of tyrosine hydroxylase (TH) in rat striatal synaptosomes. Incubation of pre-32P-labeled synaptosomes with BH4 in the presence of a permeant analogue of cAMP decreased the cAMP-stimulated level of 32P label incorporation into TH by about 50%, as determined by immunoprecipitation and autoradiography of SDS-polyacrylamide gels. The extent of inhibition mirrored changes in intrasynaptosomal BH4 levels and varied both as a function of BH4 concentration and length of incubation. A similar decrease in the amount of TH 32P-labeling was observed with the precursor of BH4, sepiapterin. This effect, in turn, was reversed by the inhibitor of sepiapterin reductase, N-acetyl-serotonin. Finally, exposure of pre-32P-labeled synaptosomes to the inhibitor of protein phosphatase 2A, okadaic acid, blocked the response to BH4. Collectively, the data suggest that BH4 stimulates the dephosphorylation of TH in situ and thus may play a dual role both as a cofactor for catalysis and a regulator of hydroxylase activity.
四氢生物蝶呤（BH4）是芳香族氨基酸羟化酶的必需辅因子，它降低了大鼠纹状体突触体中酪氨酸羟化酶（TH）的原位32P磷酸化水平。在存在cAMP通透类似物的情况下，将预先用32P标记的突触体与BH4一起孵育，通过SDS-聚丙烯酰胺凝胶的免疫沉淀和放射自显影测定，cAMP刺激的32P标记掺入TH的水平降低了约50%。抑制程度反映了突触体内BH4水平的变化，并且随BH4浓度和孵育时间而变化。用BH4的前体蝶啶观察到TH 32P标记量有类似的降低。反过来，蝶啶还原酶抑制剂N-乙酰血清素可逆转这种效应。最后，将预先用32P标记的突触体暴露于蛋白磷酸酶2A抑制剂冈田酸中，可阻断对BH4的反应。总体而言，数据表明BH4在原位刺激TH的去磷酸化，因此可能既作为催化的辅因子又作为羟化酶活性的调节剂发挥双重作用。
