Figure 6.

Differences in potential and effective cellular LDH activities and their relation to the conversion rate of hyperpolarized [1-¹³C]pyruvate-to-[1-¹³C]lactate. (A,B) Potential LDH (LDH_max) was determined in lysates from monolayer cultures using the LDH-based assay with saturating substrate concentrations. (C,D) Effective LDH activities (LDH_eff) were calculated with values of the intracellular metabolite and coenzyme concentrations (Table S1 and Figure 5) and the maximal LDH_max activity (Figure 6A,B and Table S2). Values of the speckled bars are from cell lysates after ¹³C-MRS-measurements. The Michaelis–Menten equation was applied with the assumption that NADH is already bound (K_M-values in Figure 3). The speckled bars represent values from trypsinized cells after MRS. (E,F) Ratio of k_pl to LDH_eff activity (k_pl-values from Figure 2G,H). LDH_max values were obtained from three independent experiments using lysates from monolayer cultures and from two experiments following ¹³C-MRS measurements of cell suspensions (Figure 2 and Table S2).