Isolation of mitochondrial cyclophilin from bovine heart

Peptidyl-Prolyl cis-trans isomerase was isolated from bovine heart mitochondrial matrix. The enzyme has a M(r) of 19,000 and its activity was inhibited by cyclosporin A (inhibition constant, 6.9 nM), but not by FK-506. The mitochondrial content of the enzyme is in good agreement with the number of binding sites for cyclosporin A (85 pmol/mg of matrix protein). Partial amino acid sequencing showed that the enzyme has a serine-rich N-terminal extension and is similar to human cyclophilin 3 (Bergsma et al. (1991) J. Biol. Chem. 266, 23204-23214) rather than the cytosolic and endoplasmic reticulum isoforms. We conclude that this protein is mitochondrial cyclophilin and a homologue of human cyclophilin 3.