Folding of barstar C40A/C82A/P27A and catalysis of the peptidyl‐prolyl cis/trans isomerization by human cytosolic cyclophilin (Cyp18)

Refolding of b*C40A/C82A/P27A is comprised of several kinetically detectable folding phases. The slowest phase in refolding originates from trans → cis isomerization of the Tyr47–Pro48 peptide bond being in cis conformation in the native state. This refolding phase can be accelerated by the peptidyl‐prolyl cis/trans isomerase human cytosolic cyclophilin (Cyp18) with a k_cat/K_M of 254, 000 M^–1 s^–1. The fast refolding phase is not influenced by the enzyme.