Terahertz Dielectric Response Sensitivity to Protein Oxidation State

Abstract

Previously we have shown that the terahertz dielectric response is sensitive to the oxidation state for cytochrome c (CytC) films. Here we discuss the origin of this sensitivity through hydration dependent measurements on films, solution phase measurements as a function of temperature and normal mode calculations as a function of hydration. We find that the hydration dependence of the terahertz response rapidly approaches its fully solvated value for ferri CytC, whereas for ferro CytC the effect of added water is more gradual, with the system not reaching fully hydrated values up to 0.5 gm water/gm protein. For solution phase samples below 270 K we do not see a significant difference in the terahertz response suggesting that the fully hydrated ferro cytochrome c has the same picosecond dynamics as ferri cytochrome c. These results contradict X-ray B factor measurements that suggest that ferri cytochrome c is significantly more flexible than ferro suggesting that the B-factor determination from X-ray crystal measurements may not represent in vivo values as crystal water is less than 0.5 gm water/gm protein.

Pulsed terahertz reflection imaging of tumors in a spontaneous model of breast cancer

“…This suggested that water content and lipid concentration might lead to strong changes in the terahertz reflection. Nevertheless, a number of studies have imaged biologic samples that were fixed in formalin, dehydrated, and paraffin embedded for histopathologic examination and still found contrast between tumor and the surrounding normal tissue [7][8][9][10][11][12][13] suggesting that in addition to lipid changes, other factors such as increased cell density or the presence of certain proteins may also be responsible for contrast [16].…”