Deubiquitinating enzyme tethered to the mitochondrial outer membrane that acts as a key inhibitor of mitophagy by counteracting the action of parkin (PRKN): hydrolyzes ubiquitin attached by parkin on target proteins, such as RHOT1/MIRO1 and TOMM20, thereby blocking parkins ability to drive mitophagy (PubMed:18287522, PubMed:24896179, PubMed:25527291, PubMed:25621951). Preferentially cleaves Lys-6- and Lys-11-linked polyubiquitin chains, 2 types of linkage that participate to mitophagic signaling (PubMed:25621951). Does not cleave efficiently polyubiquitin phosphorylated at Ser-65 (PubMed:25527291). Acts as negative regulator of mitochondrial fusion by mediating deubiquitination of MFN1 and MFN2 (By similarity).