Research Center for Cell and Tissue Culture, Faculty of Agriculture, Kyoto University, Kyoto 606, Japan.
Plant Physiol. 1987 Sep;85(1):145-51. doi: 10.1104/pp.85.1.145.
Dihydrodipicolinate synthase, the first enzyme unique to lysine biosynthesis in higher plants, was purified about 5100-fold from suspension-cultured cells of wheat (Triticum aestivum var Chinese Spring). The synthase has an average molecular weight of 123,000 as determined by gel filtration and exhibited maximum activity at pH 8.0. The kinetics of the condensation reaction are compatible with a "Ping Pong" mechanism in which pyruvate reacts first with the enzyme to form a Schiff base. Pyruvate and l-aspartic-beta-semialdehyde (ASA) have respective K(m) values of 11.76 and 0.80 millimolar. Allosteric inhibition was observed with increasing concentrations of l-lysine and its structural analogs, including threo-4-hydroxy-l-lysine and S-(2-aminoethyl)-l-cysteine, with respective I(0.5) values of 51, 141, and 288 micromolar. These amino acids were competitive inhibitors with respect to ASA and noncompetitive inhibitors with respect to pyruvate. We propose that the binding site for lysine overlaps with the ASA binding site, possibly by an attachment of the common alanyl moiety. The wheat enzyme was inhibited by Zn(2+), Cd(2+), and Hg(2+) and also by sulfhydryl inhibitors, p-(hydroxymercuri)benzoic acid and p-chloromercuribenzenesulfonic acid.
二氢二吡啶羧酸合酶是高等植物赖氨酸生物合成中特有的第一种酶，从小麦（中国春）悬浮培养细胞中经约 5100 倍纯化得到。该合酶的凝胶过滤平均分子量为 123000，在 pH 8.0 时表现出最大活性。缩合反应的动力学与“乒乓”机制相兼容，其中丙酮酸首先与酶反应形成希夫碱。丙酮酸和 L-天冬氨酸-β-半醛（ASA）的 K(m)值分别为 11.76 和 0.80 毫摩尔。随着 L-赖氨酸及其结构类似物（包括 threo-4-羟基-L-赖氨酸和 S-（2-氨基乙基）-L-半胱氨酸）浓度的增加，观察到别构抑制，相应的 I(0.5)值分别为 51、141 和 288 微摩尔。这些氨基酸对 ASA 为竞争性抑制剂，对丙酮酸为非竞争性抑制剂。我们提出，赖氨酸的结合位点与 ASA 的结合位点重叠，可能是通过共同的丙氨酸部分的附着。小麦酶被 Zn(2+)、Cd(2+)和 Hg(2+)以及巯基抑制剂 p-（羟基汞）苯甲酸和对氯汞苯磺酸钠抑制。
