Can bind protoporphyrin IX and may play a role in the transport of porphyrins and heme (By similarity). Promotes the transport of cholesterol across mitochondrial membranes and may play a role in lipid metabolism (PubMed:24814875), but its precise physiological role is controversial. It is apparently not required for steroid hormone biosynthesis. Was initially identified as peripheral-type benzodiazepine receptor; can also bind isoquinoline carboxamides (PubMed:1847678). Interacts with TSPOAP1 (By similarity). May interact with STAR (By similarity). Interacts with MOST-1. Found in many tissue types. Expressed at the highest levels under normal conditions in tissues that synthesize steroids. In erythrocytes, expression levels decrease throughout differentiation (PubMed:27641616). Not expressed in mature erythrocytes (PubMed:27641616). Belongs to the TspO/BZRP family.