Concerted Regulation in Vitro of Phosphoenolpyruvate Carboxylase from Escherichia coli

Ultrasensitive regulation of anapleurosis via allosteric activation of PEP carboxylase

Anapleurosis is the filling of the tricarboxylic acid cycle with four-carbon units. The common substrate for both anapleurosis and glucose phosphorylation in bacteria is the terminal glycolytic metabolite phosphoenolpyruvate (PEP). Here we show that Escherichia coli quickly and almost completely turns off PEP consumption upon glucose removal. The resulting buildup of PEP is used to quickly import glucose if it becomes available again. The switch-like termination of anapleurosis results from depletion of fructose-1,6-bisphosphate (FBP), an ultrasensitive allosteric activator of PEP carboxylase. E. coli expressing an FBP-insensitive point mutant of PEP carboxylase grow normally when glucose is steadily available. However, they fail to build up PEP upon glucose removal, grow poorly when glucose availability oscillates and suffer from futile cycling at the PEP node on gluconeogenic substrates. Thus, bacterial central carbon metabolism is intrinsically programmed with ultrasensitive allosteric regulation to enable rapid adaptation to changing environmental conditions.

Fructose-1,6-bisphosphate, a regulator of metabolism

Fructose-1,6-bisphosphate affects the rate of a large variety of enzyme reactions. In some instances its role as a physiologic effector is well documented. In many cases the effects of fructose bishosphate on particular enzymes have been demonstrated in vitro but the link to physiologic conditions has not yet been established. It is the purpose of this paper to summarize the scattered findings in fructose bisphosphate as an effector of enzyme reactions and to draw some conclusions about the role of the compound in metabolic regulation.