REACTION SPECIFICITY OF PYRIDOXAL PHOSPHATE ENZYMES

描述：磷酸吡哆醛(PLP)依赖的酶普遍存在于 氮代谢和催化许多医学上重要的转变。 作为一个基团，它们催化了非常广泛的反应，并且 与酶的设计有关的一个基本的、尚未解决的问题 抑制剂是特定的脱辅酶决定独特反应的方式 专一性。二烷基甘氨酸脱羧酶(DGD)是一种罕见的PLP依赖性酶 一种能快速催化ITS中的脱羧基和转氨基的酶 正常的催化循环，从而为深入研究 酶反应专一性的控制。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有的 结合部位。一个在活性部位附近负责激活 大离子(K+、Rb+)的影响和小离子(Na+、Li+)的抑制作用。 阐明DGD区分和IS的机制 碱金属催化控制具有非常广泛的生理功能 意义。DGD在结构上代表了一种具有重要医学意义的 一类能交替作用于伯胺的氨基转移酶 和α-氨基酸。这个项目的具体目标是测试 假设：1)C-C(脱羧基)和C-H(转氨基)键 在DGD活性中，通过单个底物结合亚位发生切割 Site，通过大的立体电子效应激活这些键；2)DGD 通过以下方式特异性地催化氧化性和非氧化性脱羧基 通过二氧化碳损失和质子的协调过渡状态 转移同时发生；3)Ser80的活动部位结构变化 和Tyr301引起的抑制离子调控的激活交换 催化活性；4)几种氨基转移酶作用于 伯胺和α-氨基酸的替代半反应是 主要由两个活性位点残基Glu215和Va1244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.