A. The optical spectra of 0.6 mM solutions of cPTIO (—), hcPTIO (---), cPTI (-·-·-) and hcPTI (·····). Spectra were recorded in quartz cuvette with light pass 4 mm. hcPTIO and hcPTI were prepared by reduction with 0.25 mM ascorbic acid. B. Representative differential optical spectra of mixture of 0.4 mM cPTIO and 0.2 mM hcPTIO after addition of 125 μM Angeli’s salt measured at time points 6.6, 13.2, 19.8, 26.4 and 46.1 min. Spectra were recorded in cuvette with light pass 4 mm. C. The kinetics of hcPTI formation from hcPTIO calculated using differential extinction coefficient at wavelength 299 nm, ε299 (hcPTIO/hcPTI) = 1.5 mM−1cm−1. Solid line represents the monoexponential approximation with τ1/2=(14±1) min.