Femtosecond study of partially folded states of cytochrome C by solvation dynamics

Using femtosecond time-resolved fluorescence spectroscopy, it is shown that the solvation dynamics in the two partially folded states (I-S' and I-S") of a protein, cytochrome C, are very different. In the case of I-S' (formed by the addition of 2 mM sodium dodecyl sulfate, SDS) almost the entire dynamic solvent shift of coumarin 153 (C153) is captured in a picosecond setup and the contribution of the ultrafast component (0.5 ps) is very small (5%). Solvation dynamics of I-S" (formed by 2 mM SDS and 5 M urea) displays a major component (47%) of 1.3 ps. This indicates that the structure of I-S" is much more open and exposed compared to that of I-S'. The difference in the dynamics of I-S' and I-S" is attributed to differences in their structure, particularly near the heme region, and the presence of urea in I-S".