Time-Resolved Vibrational Spectroscopic Study of Higher Order Structural Changes of Protein Induced by Nanosecond Temperature Jump.

点击翻译按钮获取中文摘要

A nanosecond temperature jump (T-jump) apparatus was constructed and combined with time-resolved Raman measurements to investigate thermal unfolding of a protein for the first time. The 1.56 μm-heat pulse with 9 ns width, 10 Hz was obtained through the two-step stimulated Raman scattering in D_2 gas involving seeding and amplification. To achieve uniform temperature rise, the counter-propagation geometry was adopted. The temperature rise was determined by anti-Stokes to Stokes intensity ratios of the 317 and 897 cm^<-1> bands of MoO^<2->_4 aqueous solution. The T-jump as large as 9℃ in 10 ns was attained. The unfolding of bovine pancreatic ribonuclease A was monitored with time-resolved Raman spectra excited at 532 nm. In the initial 200 ns after T-jump, the C-S stretch of Met residues exhibited 10% change of that expected from the steady state spectra and another 10% in 5 ms. The Raman intensity of S0^<2->_4 ions around 980 cm^<-1> increased at 100 μs delay and was shifted to a lower frequency than the steady state frequency of the elevated temperature, presumably due to partial release from the active site. The S-S stretches and tyrosine doublets displayed little change within 5 ms. Thus, the conformation change in the initial step of unfolding is not always concerted.