Essential component of the TIM23 complex, a complex that mediates the translocation of transit peptide-containing proteins across the mitochondrial inner membrane. Required to direct preproteins in transit and direct them to the channel protein TIM23, and possibly facilitates transfer of the translocating proteins from the TOM complex to the TIM23 complex. Does not act as a structural subunit of the TIM23 complex but plays a dynamic role in protein import. Has no phosphatase activity. Component of the TIM23 complex, at least composed of TIM23, TIM17, TIM50 and TIM21. Interacts directly with TIM23. Interacts with preproteins in transit. The mitochondrial intermembrane region is required for generation but not stabilization of the TIM23 complex. The FCP1 homology domain does not contain the canonical D-x-D-x-[TV] active site, suggesting that it probably does not display phosphatase activity. Present with 2400 molecules/cell in log phase SD medium. Belongs to the TIM50 family.