Figure 1.

Mitochondrial proteins are exceptionally longlived in tissues containing enduring postmitotic cells. (A) Whole-animal metabolic pulse ¹⁵N labeling scheme to identify and measure LLPs (≥4 mo) in mice. (B) Analytical workflow illustrating how the dissected tissues were homogenized and digested to peptides, and ¹⁵N and ¹⁴N peptides were identified and quantitated with LC-MS/MS–based proteomics. (C) Summary of protein identifications. Left plot indicates the number of ¹⁵N proteins identified (i.e., new, ≤4 mo old), right plot indicates ¹⁴N proteins identified (i.e., ≥4 mo old). (D) Tissues enriched with long-lived cells selectively harbor LLPs despite a similar number of total proteins identified in most tissues. (E) GO analysis of the LLPs in tissues that contain enduring postmitotic cells revealed that terms related to mitochondria (mito.) are significantly enriched. syn., synthesis; trans., transport. Data in C and D are mean ± SEM; in C–E, n = three mice for each tissue analyzed. *, P < 0.05; **, P < 0.01; ***, P < 0.001 by Kruskal–Wallis ANOVA with Tukey’s multiple comparisons test. See also Fig. S1 and Table S1.