Figure 7
A possible mechanism for slow growth on glucose with poor nitrogen source such as proline, glutamate or arginine.
(a) On ammonia, TCA cycle intermediates, symbolized here by αKG, are consumed rapidly for amino acid biosynthesis. (b) On proline, glutamate or arginine, TCA cycle intermediates are consumed more slowly because of nitrogen shortage. With glucose as carbon source TCA intermediates, symbolized here by αKG build up to high levels which inhibit cAMP levels. cAMP levels fall so low that important genes under control of cAMP-CRP are expressed in inappropriate levels leading to growth limitation. Importantly, uptake of glucose continues even under very low cAMP levels. (c) For other carbon sources, such as lactose, cAMP-independent uptake does not take place and their uptake is reduced severely when cAMP levels drop: this creates a feedback control system that prevents cAMP levels from going too low.
