Essential component of the TIM23 complex, a complex that mediates the translocation of transit peptide-containing proteins across the mitochondrial inner membrane. Component of the TIM23 complex at least composed of TIMM23, TIMM17 (TIMM17A or TIMM17B) and TIMM50. The complex interacts with the TIMM44 component of the PAM complex and with DNAJC15. Expression is abundant in heart and skeletal muscle, intermediate in brain, and weak in pancreas, placenta, kidney and liver. Forms one disulfide bond. Belongs to the Tim17/Tim22/Tim23 family.