Influence of isotopic substitution on the conformational dynamics of frozen proteins

The spectral diffusion dynamics was measured over 3 orders of magnitude in time of a myoglobin-type protein with the heme group substituted by Zn-pheo phorbid a. After burning a photochemical hole at 4.2 K, the width of the sp ectral diffusion kernel is well described by a power law in waiting time wi th an exponent of 0.24. Spectral diffusion broadening is subject to "aging, " viz., to the equilibration time at 4.2 K before hole burning. It decays w ith a power law in aging time. Deuteration of the solvent has a significant effect on the dynamics of the protein. Spectral diffusion broadening is sm aller in the deuterated sample, however, the respective power law is not ch anged. The aging dynamics, on the other hand, does not seem to be influence d significantly by deuteration. The conclusion is that deuteration influenc es the fluctuations but not the relaxation. In addition to spectral diffusi on, we also measured the recovery dynamics of the hole. It is slowed down t remendously by deuteration, confirming that the photoreaction is based on a light-induced proton transfer. (C) 2001 American Institute of Physics.