Import rate of amino acids. Each square symbol represents a cell line, the red solid lines indicate the expected amount given the demand of protein synthesis and the dashed red lines are linear fits to the data points. (a) Valine versus leucine import rate. (b) The import rate of serine as a function of the maximum likelihood estimate (MLE) protein synthesis rate. (c) The import rate of glycine as a function of the MLE protein synthesis rate. The cell lines below the blue dashed-dotted line export glycine. (d) The sum of serine and glycine exchange rates results in a net import that matches the overall serine and glycine requirements for protein synthesis. (e) Putative rate of serine to glycine conversion (catalyzed by serine hydroxymethyl transferase), calculated as the expected glycine supply for protein synthesis minus the observed glycine exchange. (f) Lactate excretion as a function of the glucose uptake rate. (g) Lactate excretion as a function of the MLE protein synthesis rate. The red line represents the ATP demand of protein synthesis (4.27 ATP/amino acid ). (h) Glycine exchange rate as a function of the proliferation rate. (i) Glycine exchange rate as a function of the DNA synthesis rate.