Evidence for the coordinate control of glycogen synthesis, glucose utilization, and glycolysis in Escherichia coli. II. Quantitative correlation of the inhibition of glycogen synthesis and the stimulation of glucose utilization by 2,4-dinitrophenol with the effects on the cellular levels of glucose 6-phosphate, fructose, 1,6-diphosphate, and total adenylates

Escherichia coli glycogen metabolism is controlled by the PhoP-PhoQ regulatory system at submillimolar environmental Mg2+ concentrations, and is highly interconnected with a wide variety of cellular processes

Using the Keio collection of gene-disrupted mutants of Escherichia coli, we have recently carried out a genome-wide screening of the genes affecting glycogen metabolism. Among the mutants identified in the study, Delta mgtA, Delta phoP and Delta phoQ cells, all lacking genes that are induced under low extracellular Mg2+ conditions, displayed glycogen-deficient phenotypes. In this work we show that these mutants accumulated normal glycogen levels when the culture medium was supplemented with submillimolar Mg2+ concentrations. Expression analyses conducted in wild-type, Delta phoP and Delta phoQ cells showed that the glgCAP operon is under PhoP-PhoQ control in the submillimolar Mg2+ concentration range. Subsequent screening of the Keio collection under non-limiting Mg2+ allowed the identification of 183 knock-out mutants with altered glycogen levels. The stringent and general stress responses, end-turnover of tRNA, intracellular AMP levels, and metabolism of amino acids, iron, carbon and sulfur were major determinants of glycogen levels. glgC::lacZY expression analyses using mutants representing different functional categories revealed that the glgCAP operon belongs to the RelA regulon. We propose an integrated metabolic model wherein glycogen metabolism is (a) tightly controlled by the energy and nutritional status of the cell and (b) finely regulated by changes in environmental Mg2+ occurring at the submillimolar concentration range.

Prediction of the rate of glucose utilization from cellular levels of glucose 6-phosphate and fructose 1,6-diphosphate in Escherichia coli

A comprehensive equation, upsilon = VM/[1 + (A0.5/Fru-P2)n] [ 1 + (Glc-6-P/I0.5)], has been proposed to represent the quantitative interrelationships between the rate of glucose utilization and the levels of glucose-6-phosphate and fructose-1,6-diphosphate in the intact Escherichia coli cell. This comprehensive equation was derived from empirical equations that describe the relationship between the rate of glucose utilization and one of these hexose phosphates in metabolic situations where the other hexoses phosphate was not altered. In the experiments described in this report, treatment of nitrogen (NH4+)-starved cultures of E. coli W4597 (K) with various concentrations of sodium azide altered the levels of both hexose phosphates as well as the rate of glucose utilization. In each case the observed rate and the rate predicted by the comprehensive equation agreed closely, substantiating the validity of this comprehensive relationship as a quantitative indicator of metabolic events in the intact cell. The mechanism of metabolic regulation that is represented by this equation is discussed in light of the cellular levels of adenosine 5'-triphosphate and phosphoenolpyruvate observed in these experiments.