Positively regulates mitochondrial complex assembly and/or stability (By similarity). Increases mitochondrial membrane potential while decreasing mitochondrial reactive oxygen species (PubMed:29949756). Increases mitochondrial respiration rate (PubMed:29949756). Increased mitochondrial respiratory activity promotes myogenic differentiation which facilitates muscle growth and regeneration (By similarity). Increases mitochondrial calcium retention capacity (PubMed:29949756). Plays a role in maintenance of cellular lipid composition through its interaction with cytochrome b5 reductase CYB5R3 which is required for mitochondrial respiratory complex I activity (By similarity). Interacts with the mitochondrial trifunctional enzyme complex (MTE) and enhances fatty acid beta- oxidation (PubMed:32243843). Not required for MTE formation or stability (By similarity). Modulates triglyceride clearance in adipocytes through its role in regulating fatty acid beta-oxidation and lipolysis (PubMed:32243843). {ECO:0000250|UniProtKB:Q8BT35, ECO:0000269|PubMed:29949756, ECO:0000269|PubMed:32243843}. This is the function of ENSG00000175701 (MTLN, mitoregulin).