01840nas a2200157   4500008004100000245008700041210006900128490000600197520134000203100001101543700001601554700001701570700001401587700001801601856006301619       2010                        eng d00aWhy is THz Sensitive to Protein Functional States? Oxidation State of Cytochrome C0 aWhy is THz Sensitive to Protein Functional States Oxidation Stat0 v33 a<p>We investigate the presence of structural collective motions on a picosecond time scale for the heme protein, cytochrome c, as a function of oxidation and hydration, using terahertz (THz) time-domain spectroscopy and molecular dynamics simulations. Structural collective mode frequencies have been calculated to lie in this frequency range, and the density of states can be considered a measure of flexibility. A dramatic increase in the THz response occurs with oxidation, with the largest increase for lowest hydrations and highest frequencies. For both oxidation states the measured THz response rapidly increases with hydration saturating above ~25% (g H<sub>2</sub>O/g protein), in contrast to the rapid turn-on in dynamics observed at this hydration level for other proteins. Quasi-harmonic collective vibrational modes and dipole-dipole correlation functions are calculated from the molecular dynamics trajectories. The collective mode density of states alone reproduces the measured hydration dependence providing strong evidence of the existence of these collective motions. The large oxidation dependence is reproduced only by the dipole-dipole correlation function, indicating the contrast arises from diffusive motions consistent with structural changes occurring in the vicinity of a buried internal water molecule.</p>1 aHe, Y.1 aChen, J.-Y.1 aKnab, J., R.1 aZheng, W.1 aMarkelz, A.G.  uhttp://www.tstnetwork.org/10.11906/TST.149-162.2010.12.15/