Cyclophilin‐B is an abundant protein whose conformation is similar to cyclophilin‐A

Cyclophilin‐B (bCyP‐20) was isolated in a relatively high quantity from calf brain and spleen tissues consecutively applying weak cation exchange, chromatofocusing and strong cation exchange chromatographies. Edman degradation yielded the N‐terminal sequence NH 2 ‐DEKKKGPKVTVK‐VYFDLRIGDEDIGRVVIGLFGKTVPKTVDNFVAL. Bovine cyclophilin‐B possesses the peptidylproline cis‐trans isomerase activity which is inhibited by nM concentrations of CsA. bCyP‐20 has a strong tendency to bind to cation exchangers including DNA and heparin. It could be released from DNA affinity column at concentrations of NaCl higher than 200 mM. Circular dichroism spectroscopy revealed that bovine cyclophilin‐A (bCyP‐18) and bCyP‐20 in aqueous solution have similar conformations.