posted on 2012-03-07, 00:00authored byLior Sepunaru, Noga Friedman, Israel Pecht, Mordechai Sheves, David Cahen
Electron transport (ETp) across bacteriorhodopsin (bR),
a natural
proton pump protein, in the solid state (dry) monolayer configuration,
was studied as a function of temperature. Transport changes from thermally
activated at T > 200 K to temperature independent
at <130 K, similar to what we have observed earlier for BSA and
apo-azurin. The relatively large activation energy and high temperature
stability leads to conditions where bR transports remarkably high
current densities above room temperature. Severing the chemical bond
between the protein and the retinal polyene only slightly affected
the main electron transport via bR. Another thermally activated transport
path opens upon retinal oxime production, instead of or in addition
to the natural retinal. Transport through either or both of these
paths occurs on a background of a general temperature-independent
transport. These results lead us to propose a generalized mechanism
for ETp across proteins, in which tunneling and hopping coexist and
dominate in different temperature regimes.