Apcin is an inhibitor of the anaphase-promoting complex/cyclosome (APC/C), a large multimeric complex that functions as a ubiquitin ligase, initiating the metaphase–anaphase transition and regulating ordered transitions through the cell cycle by controlling the ubiquitin-mediated proteolysis of cell cycle proteins. Apcin prevents substrate recognition and inhibits APC/C-dependent ubiquitylation by binding to the D-box binding site of Cdc20, a coactivator required for full activation of APC/C and substrate recognition. The effectiveness of apcin in blocking mitotic exit was synergistically amplified by co-addition of TAME (tosyl-L-arginine methyl ester) or its cell permeable prodrug proTAME, which block Cdc20 binding to the APC/C at a different site than apcin.

Apcin is an inhibitor of the anaphase-promoting complex/cyclosome (APC/C).