THE CIS TRANS INTERCONVERSION OF THE CALCIUM REGULATING HORMONE CALCITONIN IS CATALYZED BY CYCLOPHILIN/

The cytosolic peptidyl-prolyl cis/trans isomerase cyclophilin from pig kidney can accelerate catalytically the cis/trans isomerization of pr olyl peptide bonds. One- and two-dimensional H-1 NMR spectroscopy was used to prove that the polypeptide hormone calcitonin is a substrate f or cyclophilin. Isomerization of only one of the two prolyl peptide bo nds is catalyzed significantly. The efficiency of catalysis was calcul ated by lineshape analysis and NOESY spectroscopy. Cyclosporin A compl etely blocks the effect of the enzyme on the conformational dynamics o f the polypeptide.