We used ubiquitin (Ub) as an indirect measure of protein damage/turnover. Soluble protein samples of known concentration were diluted and 5 µg of protein was dotted on a nitrocellulose membrane as in MacLellan et al. (2015). To ensure equal protein loading, a Ponceau-S stain (Sigma-Aldrich) was applied to each membrane after imaging, according to manufacturer's instructions.