Component of the anaphase promoting complex/cyclosome (APC/C), a cell cycle-regulated E3 ubiquitin ligase that controls progression through the cell cycle (PubMed:18485873, PubMed:27120157, PubMed:27509861). Together with the RING-H2 protein ANAPC11, forms the catalytic component of the E3 ubiquitin ligase complex (PubMed:18485873, PubMed:27120157, PubMed:27509861). APC/C acts by mediating ubiquitination and subsequent degradation of target proteins: it mainly mediates the formation of 'Lys-11'-linked polyubiquitin chains and, to a lower extent, the formation of 'Lys-48'- and 'Lys-63'- linked polyubiquitin chains (PubMed:18485873). APC/C catalyzes assembly of branched 'Lys-11'-/'Lys-48'-linked branched ubiquitin chains on target proteins (PubMed:29033132). APC/C is activated by CDC20 in the metaphase/anaphase transition of cell cycle, targeting the degradation of cyclin B and securin (PubMed:27120157, PubMed:27509861). APC/C is regulated by the mitotic checkpoint complex (MCC), which inhibits APC/C and delays chromosome segregation (PubMed:27509861). May recruit the E2 ubiquitin-conjugating enzymes to the complex (PubMed:18485873). {ECO:0000269|PubMed:18485873, ECO:0000269|PubMed:27120157, ECO:0000269|PubMed:27509861, ECO:0000269|PubMed:29033132}. This is the function of CDC26 (cell division cycle 26, Ensembl gene identifier ENSG00000176386).