REACTION SPECIFICITY OF PYRIDOXAL PHOSPHATE ENZYMES

描述：磷酸吡哆醛（PLP）依赖性酶普遍存在于 氮代谢和催化许多医学上重要的转化。 作为一个群体，它们催化了非常广泛的反应， 这是一个基本的、尚未解决的问题， 抑制剂是给定的脱辅基酶如何决定独特的反应 的特异性 二烷基甘氨酸脱羧酶（DGD）是一种不寻常的PLP依赖性 一种能迅速催化脱羧作用和转氨作用的酶， 正常的催化循环，从而提供了一个工具，深入研究 酶促反应特异性的控制。 高分辨率x射线 DGD的结构是可用的，并揭示了两个碱金属离子特异性 结合位点。 一个在活性位点附近，负责激活 大离子（K+，Rb+）的作用和小离子（Na+，Li+）的抑制作用。 DGD区分和的机制的阐明， 碱金属催化调控具有非常广泛的生理活性， 意义 DGD在结构上代表了医学上重要的 一类能交替作用于伯胺的氨基转移酶 和α-氨基酸。 该项目的具体目标是测试 假设：1）C-C（脱羧）和C-H（转氨）键 裂解通过DGD活性物质中的单个底物结合亚位点发生 位点，其通过大的立体电子效应激活这些键; 2）DGD 特异性催化氧化与非氧化脱羧， 通过协调的过渡状态进行，其中CO2损失和质子 3）Ser 80活性位点的结构变化 Tyr 301由激活离子交换为抑制离子控制引起 催化活性; 4）几种氨基转移酶的作用能力， 在伯胺和α-氨基酸上的另一种半反应是 主要由两个活性位点残基Glu 215和Va 1244决定。

DESCRIPTION:Pyridoxal phosphate (PLP) dependent enzymes are ubiquitous in nitrogen metabolism and catalyze many medically important transformations. As a group, they catalyze an extraordinarily wide variety of reactions, and a fundamental, unresolved question that bears on the design of enzyme inhibitors is how a given apoenzyme determines a unique reaction specificity. Dialkylglycine decarboxylase (DGD) is an unusual PLP dependent enzyme that rapidly catalyzes both decarboxylation and transamination in its normal catalytic cycle, thereby providing a vehicle for incisive studies on the control of enzymatic reaction specificity. High resolution X-ray structures for DGD are available, and reveal two alkali metal ion-specific binding sites. One, near the active site, is responsible for the activating effects of large (K+, Rb+) and inhibitory effects of small (Na+, Li+) ions. The elucidation of the mechanisms by which DGD discriminates between and is catalytically controlled by alkali metals has very broad physiological significance. DGD is structurally representative of a medically important class of aminotransferases capable of acting alternately on primary amines and alpha-amino acids. The specific aims of this project are to test the hypotheses that: 1) C-C (decarboxylation) and C-H (transamination) bond cleavage occur via a single substrate binding subsite in the DGD active site, which activates these bonds by large stereoelectronic effects; 2) DGD specifically catalyzes oxidative vs. non-oxidative decarboxylation by proceeding through a concerted transition state in which CO2 loss and proton transfer occur simultaneously; 3) Active site structural changes in Ser80 and Tyr301 caused by exchange of activating for inhibitory ions control catalytic activity; 4) The ability of several aminotransferases to act in alternative half-reactions on primary amines and alpha-amino acids is largely determined by two active site residues, Glu215 and Va1244.