Marty-Teysset C, Lolkema J S, Schmitt P, Diviès C, Konings W N
Department of Microbiology, Groningen Biotechnology and Biomolecular Sciences Institute, University of Groningen, The Netherlands.
J Bacteriol. 1996 Nov;178(21):6209-15. doi: 10.1128/jb.178.21.6209-6215.1996.
Citrate metabolism in Leuconostoc mesenteroides subspecies mesenteroides is associated with the generation of a proton motive force by a secondary mechanism (C. Marty-Teysset, C. Posthuma, J. S. Lolkema, P. Schmitt, C. Divies, and W. N. Konings, J. Bacteriol. 178:2178-2185, 1996). The pathway consists of four steps: (i) uptake of citrate, (ii) splitting of citrate into acetate and oxaloacetate, (iii) pyruvate formation by decarboxylation of oxaloacetate, and (iv) reduction of pyruvate to lactate. Studies of citrate uptake and metabolism in resting cells of L. mesenteroides grown in the presence or absence of citrate show that the citrate transporter CitP and citrate lyase are constitutively expressed. On the other hand, oxaloacetate decarboxylase is under stringent control of the citrate in the medium and is not expressed in its absence, thereby blocking the pathway at the level of oxaloacetate. Under those conditions, the pathway is completely directed towards the formation of aspartate, which is formed from oxaloacetate by transaminase activity. The data indicate a role for citrate metabolism in amino acid biosynthesis. Internalized radiolabeled aspartate produced from citrate metabolism could be chased from the cells by addition of the amino acid precursors oxaloacetate, pyruvate, alpha-ketoglutarate, and alpha-ketoisocaproate to the cells, indicating a broad specificity of the transamination reaction. The alpha-ketocarboxylates are readily transported across the cytoplasmic membrane. alpha-Ketoglutarate uptake in resting cells of L. mesenteroides was dependent upon the presence of an energy source and was inhibited by inhibition of the proton motive force generating F(0)F(1) ATPase and by selective dissipation of the membrane potential and the transmembrane pH gradient. It is concluded that in L. mesenteroides alpha-ketoglutarate is transported via a secondary transporter that may be a general alpha-ketocarboxylate carrier.
肠系膜明串珠菌肠系膜亚种中的柠檬酸代谢与通过二级机制产生质子动力相关（C. Marty-Teysset、C. Posthuma、J. S. Lolkema、P. Schmitt、C. Divies和W. N. Konings，《细菌学杂志》178:2178 - 2185，1996年）。该途径包括四个步骤：（i）柠檬酸的摄取，（ii）柠檬酸分解为乙酸盐和草酰乙酸，（iii）草酰乙酸脱羧形成丙酮酸，以及（iv）丙酮酸还原为乳酸。对在有或无柠檬酸存在的情况下生长的肠系膜明串珠菌静息细胞中柠檬酸摄取和代谢的研究表明，柠檬酸转运蛋白CitP和柠檬酸裂合酶是组成型表达的。另一方面，草酰乙酸脱羧酶受到培养基中柠檬酸的严格调控，在没有柠檬酸时不表达，从而在草酰乙酸水平阻断该途径。在这些条件下，该途径完全导向天冬氨酸的形成，天冬氨酸是由草酰乙酸通过转氨酶活性形成的。数据表明柠檬酸代谢在氨基酸生物合成中起作用。通过向细胞中添加氨基酸前体草酰乙酸、丙酮酸、α - 酮戊二酸和α - 酮异己酸，可以将由柠檬酸代谢产生的内化放射性标记天冬氨酸从细胞中追踪出来，这表明转氨反应具有广泛的特异性。α - 酮羧酸盐很容易穿过细胞质膜。肠系膜明串珠菌静息细胞中α - 酮戊二酸的摄取依赖于能量源的存在，并受到产生质子动力的F(0)F(1) ATP酶的抑制以及膜电位和跨膜pH梯度的选择性耗散的抑制。得出的结论是，在肠系膜明串珠菌中，α - 酮戊二酸通过一种二级转运体转运，该转运体可能是一种通用的α - 酮羧酸盐载体。
