Abstract
We studied the effects of decreased aeration, chloramphenicol succinate, and 2,4-dinitrophenol on the cellular rates of glycogen synthesis and glucose utilization and on the cellular concentrations of adenine nucleotides, glucose 6-phosphate, fructose 1,6-diphosphate, and phosphoenolpyruvate during the first two periods of nitrogen starvation of Escherichia coli W4597(K). A quantitative relationship between the changes in the rates and the accompanying changes in the hexose phosphates is demonstrated. However, the relationship for glycogen synthesis is different in different sets of metabolic conditions. We suggest that this difference reflects a change in the steady state level of a previously unknown effector of ADP-glucose synthetase (glucose 1-phosphate adenylyltransferase, EC 2.7.7.27) the rate-limiting enzyme of bacterial glycogen synthesis. We show that the properties of the hypothetical in vivo effector are consistent with the inhibitory effects of ppGpp (guanosine 3'-diphosphate 5'-diphosphate) and pppGpp (guanosine 3'-diphosphate 5'-triphosphate) on this enzyme in vitro. In addition, tetracycline, an inhibitor of the synthesis of these nucleotides, apparently prevents the change in the quantitative relationship. The relationship between glucose utilization and the hexose phosphates is altered at the transition to Period II of nitrogen starvation. We propose that this change reflects the alteration of the cellular steady state level of an unknown effector of the glucose phosphotransferase system. In contrast to the ATP-hexose phosphate system of shared regulatory effects, the specific effects of the unknown effectors allow the rates of glucose utilization and glycogen synthesis to be altered independently of each other and independently of changes in the rate of glycolysis. This independence allows a greater latitude of response for the individual pathways in more severe metabolic stress or in accommodating the metabolic changes necessary for long term survival.
Highlights
We studied the effects of decreased aeration, chloramphenicol succinate, and 2,4-dinitrophenol on the cellular rates of glycogen synthesis and glucose utilization and on the cellular concentrations of adenine nucleotides, glucose 6-phosphate, fructose 1,6-diphosphate, and phosphoenolpyruvate during the first two periods of nitrogen starvation of Escherichia coli W4597(K)
During the first 4 h of nitrogen starvation the increase in cellular glycogen and the decrease in glucose in the medium were linear over time, that is, during this period the rates of glycogen synthesis and glucose utilization were constant
As we have observed previously (l), after about 4 h of nitrogen starvation these constant rates shifted simultaneously and abruptly to different constant rates (Fig. 1). These newly established rates were maintained throughout the 6 h of nitrogen starvation. We have designated these two periods in which the rates of glycogen synthesis and glucose utilization are constant as Periods I and II of nitrogen starvation
Summary
The relationship between glucose utilization and the hexose phosphates is altered at the transition to Period II of nitrogen starvation We propose that this change reflects the alteration of the cellular steady state level of an unknown effector of the glucose phosphotransferase system. At the transition from Period I to Period II of nitrogen starvation or when a certain degree of metabolic stress arises, additional regulatory factors are apparently introduced These factors appear to have exclusive effects on either glycogen synthesis or glucose utilization, allowing a more independent regulation of these processes during severe metabolic stress or metabolic reorganization related to long term survival
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
