The characterization of a cyclophilin-type peptidyl prolyl cis-trans-isomerase from the endoplasmic-reticulum lumen.

A luminally located peptidyl prolyl cis-trans-isomerase (PPI) has been purified from bovine liver microsomes. It has a molecular mass of 20.6 kDa, and N-terminal sequencing demonstrates strong sequence similarity to the sequences of the cyclophilin B family. The enzyme catalyses the isomerization of the standard proline-containing peptide N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide, as well as the refolding of RNAase T1. Kinetic properties, substrate-specificity data and inhibition by cyclosporin A indicate that it is a cyclophilin-type PPI, consistent with the amino-acid-sequence results.