Stringent control of intermediary metabolism in Escherichia coli: pyruvate excretion by cells grown on succinate.
A large amount of pyruvate was excreted into the medium by CP78 (rel+) cells grown on succinate when they were starved for amino acids. In contrast, no such excretion was observed with CP79 (rel-) cells. This phenomenon was also seen with two other isogenic pairs of strains: NF161 (rel+) and NF162 (rel-), and 10B601 (rel+) and 10B602 (rel-). Besides succinate, L-malate, and fumarate were effective carbon sources for the excretion, but glucose, glycerol, and acetate were not. When DL-lactate was used, not only CP78 but also CP79 cells excreted pyruvate. Experiments using [1,4-14C]succinate as a carbon source revealed that pyruvate was formed by decarboxylation of one carboxyl group of succinate and that the pyruvate excretion amounted to about 40% of the total succinate degraded. Experiments designed to elucidate the mechanism of the excretion yielded the following observations. (i) The concentration of pyruvate in CP78 cells grown on the C4-dicarboxylic acids mentioned above was not significantly changed upon amino acid starvation. (ii) Guanosine 5'-diphosphate-3'-diphosphate exerted no effect on the activities of several enzymes thought to be involved in pyruvate-related metabolism. It is suggested firstly that the excretion was not due to some impairment in the biosynthetic pathway of a particular amino acid, but was due to the stringent control of central amphibolic metabolism, and secondly that no de novo protein synthesis was involved in the excretion.
D000596:Amino Acids / Q000502:physiology; D003470:Culture Media / Q000032:analysis; D004926:Escherichia coli / Q000378:metabolism*; D006159:Guanosine Tetraphosphate / Q000494:pharmacology; D007651:Keto Acids / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism*; D019289:Pyruvic Acid; D013386:Succinates / Q000378:metabolism*
D000596:Amino Acids; D003470:Culture Media; D007651:Keto Acids; D011773:Pyruvates; D013386:Succinates; D006159:Guanosine Tetraphosphate; D019289:Pyruvic Acid