Deuterium isotope effects on the central carbon metabolism of Escherichia coli cells grown on a D2O-containing minimal medium

Isotope effects on the central carbon metabolism due to the addition of var iable amounts of D2O (0 to 70%) were investigated with biosynthetically dir ected fractional C-13-labeling for Escherichia coli BL21(DE3) cells during exponential growth on a M9 minimal medium containing a mixture of 70% unlab eled and 30% uniformly C-13-labeled glucose as the sole carbon source. The resulting C-13-labeling patterns in the amino acids were analysed by two-di mensional [C-13,H-1]-correlation spectroscopy. With the aforementioned grow th conditions, higher D2O contents resulted in an increase of the anaplerot ic supply of the tricarboxylic acid cycle via carboxylation of phosphoenolp yruvate when compared to the influx of acetyl-CoA. Furthermore, the additio n of D2O affected the C-1 metabolic pathways that involve Ser and Gly. Othe rwise the E. coli cells showed identical topologies of the active biosynthe tic pathways in H2O and at elevated D2O contents, and the metabolic flux ra tios characterizing glycolysis and the pentose phosphate pathway were not m easurably affected by the addition of D2O. Cells that had been adapted for growth in D2O exhibited the same response to the presence of D2O in the nut rient medium as non-adapted cells. Implications of these data for the prepa ration of recombinant deuterated proteins for NMR studies are discussed.