Updated project metadata. Biosynthesis of mitochondrial genome-encoded proteins is carried out by the mitoribosome, a specialized apparatus that has evolved and diverged dramatically since its bacterial origin. Recent studies across various eukaryotes have demonstrated widespread structural and compositional diversity of mitoribosomes. We used sucrose gradient centrifugation and Blue-Native PAGE to separate mitoribosomes of Diplonema papillatum, the type species of diplonemids, a widespread group of single-celled marine flagellates.