MECHANISMS OF PYRIDOXAL 5' PHOSPHATE DEPENDENT ENZYMES

含有吡哆醛-5 '-磷酸（PLP）的酶，也称为维生素B6， 在生物学中无处不在，在代谢中进行重要反应， 氨基酸和胺。 这些酶催化各种各样的 反应，包括外消旋化、转氨作用、α-和β- 脱羧、逆向醛醇裂解、β-和γ-消除和 替代。 PLP依赖性酶在代谢中的核心作用 氨基酸和胺的合成，以及重要生物活性物质的生物合成 代谢物，使它们成为机制设计的有吸引力的目标- 的抑制剂，其可用作药物。 碳碳裂解酶 （酪氨酸酚裂解酶和色氨酸吲哚裂解酶）是细菌酶 其催化L-酪氨酸或L-酪氨酸的水解β-消除， 色氨酸，分别得到苯酚或吲哚和丙酮酸铵。 这些酶是研究结构之间关系的理想模型 和PLP酶的机制。 它们的结构和机制 酶将通过诱变，X射线晶体学和预- 稳态动力学 犬尿氨酸酶催化 L-犬尿氨酸得到邻氨基苯甲酸和L-丙氨酸。 在真核 生物体，犬尿氨酸酶的产物，3-羟基邻氨基苯甲酸， 通过双加氧酶进行环裂解，得到α-氨基-β- 羧基粘康酸半醛，其可以自发地环化， 喹啉酸，一种已知的神经毒素。 犬尿氨酸酶的抑制剂可以 因此在一些严重的神经系统疾病的治疗中具有价值， 如亨廷顿舞蹈病、ALS、中风、癫痫和艾滋病相关 痴呆 为了帮助设计新的抑制剂，犬尿氨酸酶 将被克隆，测序，并确定三维结构。 去年，nifS的产物被发现是一种PLP依赖性酶 其催化L-半胱氨酸的脱硫产生L-丙氨酸， 元素硫 有人提出，这种酶是必需的， 铁硫中心的体外合成，这是必要的， 电子转移过程，因此在生物学中普遍存在。 的 L-半胱氨酸脱硫酶的作用机理将通过稳态和 预稳态动力学方法。 我们持续研究的结果 很可能会对改善 未来美国人的医疗保健

Enzymes containing pyridoxal-5'-phosphate (PLP), also known as vitamin B6, are ubiquitous in biology, performing essential reactions in metabolism of amino acids and amines. These enzymes catalyse a wide variety of reactions, including racemization, transamination, alpha- and beta- decarboxylation, retro-aldol cleavage, beta- and gamma-elimination and substitution. The central role of PLP-dependent enzymes in the metabolism of amino acids and amines, and the biosynthesis of important bioactive metabolites, makes them attractive targets for the design of mechanism- based inhibitors, which may be useful as drugs. The carbon-carbon lyases (tyrosine phenol-lyase and tryptophan indole-lyase) are bacterial enzymes which catalyse the hydrolytic beta-elimination of L-tyrosine or L- tryptophan to give, respectively, phenol or indole, and ammonium pyruvate. These enzymes are ideal models to study the relationship between structure and mechanisms in PLP enzymes. The structures and mechanisms of these enzymes will be studied by mutagenesis, X-ray crystallography, and pre- steady-state kinetics. Kynureninase catalyses the hydrolytic cleavage of L-kynurenine to give anthranilic acid and L-alanine. In eucaryotic organisms, the product of kynureninase, 3-hydroxyanthranilic acid, undergoes ring cleavage by a dioxygenase to give alpha-amino-beta- carboxymuconic semialdehyde, which can cyclize spontaneously to give quinolinic acid, a known neurotoxin. Inhibitors of kynureninase could thus be of value in the treatment of some serious neurological disorders, such as Huntington's chorea, ALS, stroke, epilepsy, and AIDS-related dementia. In order to aid in the design of new inhibitors, kynureninase will be cloned, sequenced, and the three dimensional structure determined. Last year, the product of nifS was found to be a PLP-dependent enzyme which catalyses the desulfurization of L-cysteine to give L-alanine and elemental sulfur. It has been proposed that this enzyme is required for the in vitro synthesis of iron-sulfur centers, which are necessary for electron transfer processes and are thus ubiquitous in biology. The mechanism of L-cysteine desulfurase will be studied by steady-state and pre-steady-state kinetic methods. The results of our continuing research are likely to make a significant contribution to the goal of improving health care for Americans in the future.