PPIase activity assay. The PPIase activities of CrTIG1 and EcTF were measured with a protease-coupled assay. The prolyl cis–trans isomerization of the tetrapeptide succinyl-Ala-Phe-Pro-Phe-para-nitroanilide as a substrate was monitored by measuring the absorbance changes at 395 nm at different CrTIG1 concentrations. EcTF was used as a positive control. The inset shows the change of the rate constants depending on the CrTIG1 concentration.