Fig. 3.

TCA cycle-triggered membrane depolarization. a Summary of metabolic flux through the TCA cycle in the presence of serum, serum plus glycine, or glycine. Change in metabolite abundance is indicated as follows: red, upregulation; green, down-regulation; gray, not detected. NAD⁺, nicotinamide adenine dinucleotide; NADH, reduced nicotinamide adenine dinucleotide (n = 6). b NADH concentration in E. coli K12 and Y17 in the presence of 100 μL serum, 100 mM glycine or both for 2 h (n = 3). c, d Membrane potential (c) and percent survival (d) of E. coli K12 and Y17 treated with 100 µL serum for 2 h in presence or absence of 100 mM glycine or/and CCCP (n = 3). For membrane potential, 50,000 cells were recorded with forwarding versus side scatter and were gated before data acquisition. e Percent survival of E. coli, ΔatpA, ΔatpC, and ΔatpD in the presence of 100 mM glycine, 100 µL serum, or both for 2 h (n = 3). f Mass isotopomer distributions for ¹³C labeled glycine detected in a nontargeted manner in the presence of 100 mM glycine. The relative flux for that metabolite in the TCA cycle (υ_TCA/υ_GLY) is defined (M2 + M3 + M4)/(M1 + M2 + M3) ratio, where υ_TCA refers to the turnover of a particular metabolite pool and υ_GLY refers to the flux of glycine carbon atoms to the TCA cycle. g qRT-PCR for relative expression of genes contributed to the flux from serine to the upper TCA cycle in the presence or absence of 100 mM glycine (n = 3). Results are displayed as mean ± SEM (b–g), and significant differences are identified (*p < 0.05, **p < 0.01) as determined by two-tailed Student’s t test (a–e, g)