StAR and TSPO are involved in the transport of cholesterol from the outer mitochondrial membrane (OMM) to the IMM, which is a highly regulated step. In the IMM, cholesterol is transformed into pregnenolone by P450scc, the first steroidogenic enzyme. StAR, TSPO and P450scc form a multimolecular complex, termed the transduceosome, together with other proteins, including the 31 kDa voltage-dependent anion-selective channel (VDAC) in the OMM and the 35 kDa mitochondrial adenine nucleotide translocator (ANT) in the IMM143. Pregnenolone is then converted to other steroids through a series of consecutive steps (see the figure, right panel) in the endoplasmic reticulum.