Synthesis and Release of Biogenic Amines

酪氨酸羟化酶（TH）催化酪氨酸羟化为二氢苯丙氨酸，是儿茶酚胺生物合成的限速步骤。该反应需要将分子氧还原为水，其中氧原子并入酪氨酸的芳环中。TH依赖于四氢生物蝶呤以及非血红素铁的活性。苯丙氨酸羟化酶（PAH）和TH系统的现有证据表明，氢过氧四氢生物蝶呤是羟化物种。铁的作用尚不清楚;然而，在无铁TH中缺乏活性与Fe在催化中具有重要作用是一致的。建议Fe促进过氧中间体的形成，而Fe氧代中间体作为羟基化物种尚未被排除。目前的研究主要集中在羟化物种的TH反应和化学计量和反应物的结合顺序的识别。 通过用氧电极监测密封室中的反应，已经获得了初步结果。在空气饱和的缓冲液中，在没有酪氨酸的情况下，每摩尔TH活性位点消耗一摩尔分子氧。 这种氧摄取似乎依赖于四氢生物蝶呤而不是酪氨酸，这表明氧依赖性羟基化物质的形成可能与酪氨酸依赖性羟基化分开。进一步的研究正在进行中，以确认这些结果，以及从羟基化步骤分离氧活化到单独的好氧和厌氧反应。

Tyrosine hydroxylase (TH) catalyzes the hydroxylation of tyrosine to dihydrophenylalanine in the rate limiting step of catecholamine biosynthesis. The reaction requires the reduction of molecular oxygen to water with an oxygen atom incorporated into the aromatic ring of tyrosine. TH is dependent on tetrahydrobiopterin as well as a non-heme iron for activity. Current evidence for both the phenylalanine hydroxylase (PAH) and TH systems suggests that a hydroperoxytetrahydrobiopterin is the hydroxylating species. The role of the iron is unclear; however, the lack of activity in iron-free TH is consistent with the Fe having an essential role in catalysis. The Fe is proposed to facilitate the formation of the peroxy intermediate while an Fe oxo intermediate as the hydroxylating species has not been ruled out. Present studies are focused on the identification of the hydroxylating species of the TH reaction and the stoichiometry and order of binding of the reactants. Preliminary results have been obtained by monitoring the reaction in a sealed chamber with an oxygen electrode. In air-saturated buffer one mole of molecular oxygen is consumed for each mole of TH active sites in the absence of tyrosine. This oxygen uptake appears to be dependent on tetrahydrobiopterin and not tyrosine, evidence that the oxygen dependent formation of the hydroxylating species may be separate from the tyrosine dependent hydroxylation. Further studies are underway to confirm these results as well as to isolate the oxygen activation from the hydroxylation steps into separate aerobic and anaerobic reactions.