Lazarus R A, Wallick D E, Dietrich R F, Gottschall D W, Benkovic S J, Gaffney B J, Shiman R
Fed Proc. 1982 Jul;41(9):2605-7.
The site of oxygen binding during phenylalanine hydroxylase (PAH)-catalyzed turnover of phenylalanine to tyrosine has been tentatively identified as the 4a position of the tetrahydropterin cofactor, based on the spectral characteristics of an intermediate generated from both 6-methyltetrahydropterin and tetrahydrobiopterin during turnover. The rates of appearance of the intermediate and tyrosine are equal. Both rates exhibit the same dependence on enzyme concentration. PAH also requires 1.0 iron per 50,000-dalton subunit for maximal activity. A direct correlation between iron content and specific activity has been demonstrated. Apoenzyme can be reactivated by addition of Fe(II) aerobically or Fe(III) anaerobically and can be repurified to give apparently native protein. Evidence from electron paramagnetic resonance implicates the presence of high spin (5/2) Fe(III). As a working hypothesis we postulate that a key complex at the active site may be one containing iron in close proximity to a 4a-peroxytetrahydropterin.
基于苯丙氨酸羟化酶（PAH）催化苯丙氨酸向酪氨酸转化过程中生成的中间体的光谱特征，已初步确定四氢蝶呤辅因子的4a位是氧气结合位点，该中间体由6-甲基四氢蝶呤和四氢生物蝶呤在转化过程中生成。中间体和酪氨酸的出现速率相等。两种速率对酶浓度的依赖性相同。PAH每50,000道尔顿亚基还需要1.0个铁原子才能达到最大活性。已证明铁含量与比活性之间存在直接相关性。脱辅基酶可以通过需氧添加Fe(II)或厌氧添加Fe(III)重新激活，并可以重新纯化以得到明显天然的蛋白质。电子顺磁共振的证据表明存在高自旋（5/2）Fe(III)。作为一个工作假设，我们假定活性位点的一个关键复合物可能是一个铁与4a-过氧四氢蝶呤紧密相邻的复合物。
