Okuno S, Fujisawa H
J Biol Chem. 1985 Mar 10;260(5):2633-5.
Tyrosine 3-monooxygenase activity of the crude extract from rat striatum had a sharp pH optimum at pH 5.4 and showed almost no activity at or above pH 7. When the crude extract was partially purified by pH precipitation and chromatography on DEAE-cellulose, the enzyme showed a high activity in the pH range of 5.8 to 7.4. Incubation of the partially purified enzyme with catecholamines such as dopamine, norepinephrine, and epinephrine resulted in a remarkable decrease in the enzyme activity, as assayed at a neutral pH. This suppression of the enzyme activity by catecholamines differed from the well-known feedback inhibition which is competitive with respect to the pterin cofactor; the former occurred at a very much lower concentration of catecholamines even in the presence of a near-saturating concentration of a pterin cofactor, and the former was a time-dependent reaction. The enzyme, the activity of which had been suppressed by the incubation with dopamine, was remarkably activated by the incubation with the catalytic subunit of cyclic AMP-dependent protein kinase in the presence of an ATP-generating system. These results suggest that the activity of tyrosine 3-monooxygenase may be suppressed by its end products in a normal state and it may be stimulated by cyclic AMP-dependent protein kinase as occasion demands.
大鼠纹状体粗提物的酪氨酸3-单加氧酶活性在pH 5.4时具有尖锐的最适pH值，在pH 7或更高时几乎没有活性。当粗提物通过pH沉淀和DEAE-纤维素柱层析进行部分纯化时，该酶在5.8至7.4的pH范围内表现出高活性。在中性pH下测定，将部分纯化的酶与多巴胺、去甲肾上腺素和肾上腺素等儿茶酚胺一起孵育，导致酶活性显著降低。儿茶酚胺对该酶活性的这种抑制作用不同于众所周知的反馈抑制，后者对蝶呤辅因子具有竞争性；前者即使在蝶呤辅因子接近饱和浓度的情况下，也在非常低的儿茶酚胺浓度下发生，并且前者是一种时间依赖性反应。与多巴胺孵育后活性受到抑制的酶，在存在ATP生成系统的情况下，与环磷酸腺苷依赖性蛋白激酶的催化亚基一起孵育时会被显著激活。这些结果表明，酪氨酸3-单加氧酶的活性在正常状态下可能被其终产物抑制，并且可能根据需要被环磷酸腺苷依赖性蛋白激酶刺激。
