Saccharopine, a lysine degradation intermediate, is a mitochondrial toxin

Saccharopine, a nonproteinogenic amino acid originally isolated from the yeast Saccharomyces cerevisiae, is an intermediate in lysine metabolism. In this issue, Zhou et al. (2019. J. Cell Biol. https://doi.org./10.1083/jcb.201807204) show that abnormal accumulation of saccharopine results in defective mitochondrial dynamics and function in worm and mouse models.