Neijssel O M, Buurman E T, Teixeira de Mattos M J
Department of Microbiology, University of Amsterdam, The Netherlands.
Biochim Biophys Acta. 1990 Jul 25;1018(2-3):252-5. doi: 10.1016/0005-2728(90)90260-b.
In this contribution we describe the occurrence of futile cycles in growing bacteria. These cycles are thought to be active when organisms contain two uptake systems for a particular nutrient (one with a high, the other with a low affinity for its substrate). The high-affinity system is responsible for uptake of the nutrient, some of which is subsequently lost to the medium again via leakage through the low-affinity-system. A special futile cycle is caused under some growth conditions by the extremely rapid diffusion of ammonia through bacterial membranes. When the ammonium ion is taken up via active transport, the couple NH3/NH4+ will act as an uncoupler. This is aggravated by the chemical similarity of the potassium and the ammonium ion, which leads to ammonium ion transport via the Kdp potassium transport system when the potassium concentration in the medium is low. Other examples of futile cycles, such as those caused by the production of fatty acids by fermentation, are briefly discussed.
在本论文中，我们描述了生长中的细菌中无效循环的发生情况。当生物体含有针对特定营养物质的两种摄取系统（一种对其底物具有高亲和力，另一种具有低亲和力）时，这些循环被认为是活跃的。高亲和力系统负责营养物质的摄取，其中一些随后会通过低亲和力系统渗漏回培养基中。在某些生长条件下，氨通过细菌膜的极快速扩散会导致一种特殊的无效循环。当铵离子通过主动运输被摄取时，NH3/NH4+ 对会起到解偶联剂的作用。钾离子和铵离子的化学相似性加剧了这种情况，当培养基中的钾浓度较低时，会导致铵离子通过Kdp钾转运系统进行运输。本文还简要讨论了其他无效循环的例子，例如发酵产生脂肪酸所导致的无效循环。
