Nanosecond-time-resolved infrared spectroscopic study of fast relaxation kinetics of protein folding by means of laser-induced temperature-jump

Elucidating the initial kinetics of folding pathways is critical to the understanding of the protein folding mechanism. Transient infrared spectroscopy has proved a powerful tool to probe the folding kinetics. Herein we report the construction of a nanosecond laser-induced temperature-jump (T-jump) technique coupled to a nanosecond time-resolved transient mid-infrared (mid-IR) spectrometer system capable of investigating the protein folding kinetics with a temporal resolution of 50 ns after deconvolution of the instrumental response function. The mid-IR source is a liquid N_2 cooled CO laser covering a spectral range of 5.0\mum (2000 cm^-1) \sim 6.5\mum (1540 cm^-1). The heating pulse was generated by a high pressure H_2 Raman shifter at wavelength of 1.9\mum. The maximum temperature-jump could reach as high as 26\pm 1^\circC. The fast folding/unfolding dynamics of cytochrome C was investigated by the constructed system, providing an example.