BAP37, (also known as B-cell receptor-associated protein, repressor of estrogen receptor activity, and prohibitin 2) is a 37 kD erythrocyte band 7 integral membrane protein that contains an SPFH domain. BAP37 is located in the inner mitochondrial membrane that selectively potentiates the inhibitory effectiveness of antiestrogen-occupied ER. BAP37 plays a possible role in cell aging and acts as a mitochondrial protein chaperone. This protein has been shown to interact with the estrogen receptor, prohibitin, and IgM. The Poly6118 antibody has been shown to be useful for Western blotting of the human and mouse BAP37 protein.