Regulation of Amino Acid Biosynthesis

葡糖激酶在细菌氨基酸生物合成中起核心作用。它催化天冬氨酸途径的第一步，其产物包括成人营养所必需的八种氨基酸中的四种。天冬氨酸途径的控制很大程度上取决于天冬氨酸激酶同工酶的存在，其在合成和活性的调节方面不同。我们在过去两年中的主要研究成果包括在遗传，酶，和生理水平的完整的枯草芽孢杆菌的葡激酶同工酶模式的一般定义和详细的特性的操纵子，编码这些同工酶之一，葡激酶II（AKII）。拟议的研究的主要目的是研究控制AKII操纵子表达的分子机制，AKII通过其反馈抑制剂L-赖氨酸的变构调节模式，以及AKII的两个不同亚基的生理功能。在AKII研究进行的同时，将开始一项平行的研究，重点关注B的其他天冬氨酸激酶同工酶。枯草杆菌，其中一种（AKI）被细胞壁抑制，构成二氨基苯二酸，另一种（AKIII）被苏氨酸和赖氨酸抑制。AKI主要在富培养基中生长期间合成二氨基庚二酸中起作用，并且在孢子形成期间产生二氨基庚二酸和吡啶二羧酸中起作用，而AKII和AKIII在生长细胞中生物合成赖氨酸、苏氨酸和甲硫氨酸中起作用。初步实验将涉及编码AKI和AKIII的基因的克隆和测序，随后将研究调节这些酶的合成和活性的机制。对这些重要调控酶的深入研究将有助于我们理解代谢调控的原理和策略。

The enzyme aspartokinase plays a central role in bacterial amino acid biosynthesis. It catalyzes the first step in the aspartate pathway, whose products include four of the eight amino acids that are essential for the nutrition of the adult human. The control of the aspartate pathway depends largely on the presence of isozymes of aspartokinase, which differ in the regulation of their synthesis and activity. Our major research accomplishments in the last two years include the general definition at the genetic, enzymatic, and physiological level of the complete aspartokinase isozyme pattern of Bacillus subtilis and the detailed characterization of the operon that encodes one of these isozymes, aspartokinase II (AKII). The primary aim of the proposed research is to study the molecular mechanisms controlling the expression of the AKII operon, the mode of allosteric regulation of AKII by its feedback inhibitor L- lysine, and the physiological function of the two non-identical subunits of AKII. A parallel line of investigation, to be begun while the studies on AKII are in progress, will focus on the other aspartokinase isozymes of B. subtilis, of which one (AKI) is inhibited by the cell wall constitute diaminopmelate and the other (AKIII) by threonine and lysine. AKI functions primarily in the synthesis of diaminopimelate during growth in rich media and in the production of diaminopimelate and dipicolinate during sporulation, whereas AKII and AKIII serve in the biosynthesis of lysine, threonine, and methionine in growth cells. Initial experiments will involve the cloning and sequencing of the genes encoding AKI and AKIII and will be following by the study of the mechanisms that regulate the synthesis and activity of these enzymes. The in-depth study of the control of these important regulatory enzymes will contribute fundamentally to our understanding of the principles and strategies of metabolic regulation.