Figure 4. Stable isotope tracing reveals substantial contribution of protein scavenging to amino acid pools.
(A) Schematic of isotope tracing experiment enabling separate quantification of amino acids derived from serum protein and amino acids initially taken up as monomers. (B, C) Fractional contribution of extracellular protein to intracellular (B) and extracellular (C) amino acid pools in KRPC cells. (D, E) Bafilomycin A1, an inhibitor of lysosomal acidification, reduces intracellular (D) and extracellular (E) serum protein-derived amino acid pools in a dose-dependent fashion. For B–E, data are means ± SE of n ≥ 3.