Bif is a protein of 40 kDa that may be required for normal outer mitochondrial membrane dynamics and for coatomer-mediated retrograde transport in certain cells. It may recruit other proteins to membranes and may promote membrane fusion. It localizes to Golgi apparatus membrane as well as mitochondrion outer membrane, but association with the Golgi apparatus depends on the cell type. Expression is found in heart, skeletal muscle, kidney, and placenta, in brain, colon, thymus, spleen, liver, small intestine, lung, and peripheral blood leukocytes.