Optical Triggers of Protein Folding

In our report about the electron-transfer (ET)-initiated folding of ferrocytochrome c (cyt c^(II)) (1), we noted rapid changes the visible absorption spectrum corresponding to a process with a time constant of ~40 µs. We indicated that this observation consistent with studies of cyt c^(ll) folding by CO dissociation where the fast were attributed to changes in heme (2). We also suggested that these might correspond to the collapse of protein into a compact denatured state, as been proposed for apomyoglobinon the of laser-temperature-jump measurements (3). Our transient absorption data could not between the two possibilities, and fast folding dynamics were a relatively component of the study described in report. Chan et al., with the use of tryptophan (Trp) fluorescence as a probe, found significant collapse of the protein on the time scale following dissociation CO from unfolded cyt c^(II). Clearly, pectroscopic probes must be employed study protein folding; accordingly, are currently developing time-resolved Trp as a probe for ET-initiated folding cyt c^(II).