Forman M, Aronson A
Biochem J. 1972 Feb;126(3):503-13. doi: 10.1042/bj1260503.
Some of the early enzymes in the lysine-biosynthetic pathway also function for dipicolinic acid synthesis in sporulating Bacillus cereus T. 1. The first enzyme, aspartokinase, loses its sensitivity to feedback inhibition by lysing. This change occurs before the time of dipicolinic acid synthesis but at a time when diaminopimelic acid is required for spore cortex formation. 2. A possible regulatory change at a branch point in the pathway was studied by examining the properties of a key enzyme, dihydrodipicolinic acid reductase. No alteration in the feedback sensitivity or sedimentation rate of this enzyme could be detected during sporulation. 3. Two mutants producing heat-sensitive spores were analysed. Both produced spores that contained decreased amounts of dipicolinic acid. Although neither was a lysine auxotroph, they both had greatly decreased activities of certain lysine-biosynthetic enzymes in sporulating cells. 4. Starvation of cells for calcium also results in the production of spores that are heat-sensitive and contain less dipicolinic acid than the control. A decreased content of one of the lysine-biosynthetic enzymes, dihydrodipicolinic acid synthetase, in calcium-starved cells could account for the lower concentration of dipicolinic acid in the spores.
赖氨酸生物合成途径中的一些早期酶在蜡样芽孢杆菌T. 1形成芽孢的过程中也参与吡啶二羧酸的合成。1. 第一种酶，天冬氨酸激酶，通过裂解失去对反馈抑制的敏感性。这种变化发生在吡啶二羧酸合成之前，但在芽孢皮层形成需要二氨基庚二酸的时候。2. 通过研究关键酶二氢吡啶二羧酸还原酶的性质，对该途径分支点处可能的调节变化进行了研究。在芽孢形成过程中未检测到该酶的反馈敏感性或沉降速率有改变。3. 分析了两个产生热敏性芽孢的突变体。两者产生的芽孢中吡啶二羧酸含量均降低。虽然两者都不是赖氨酸营养缺陷型，但在形成芽孢的细胞中，它们的某些赖氨酸生物合成酶的活性都大大降低。4. 细胞缺乏钙也会导致产生热敏性芽孢，且其吡啶二羧酸含量比对照少。钙缺乏细胞中赖氨酸生物合成酶之一二氢吡啶二羧酸合成酶的含量降低，这可以解释芽孢中吡啶二羧酸浓度较低的原因。
