Low-energy dynamics and biological function

Abstract

Results from QENS experiments using a resolution of 93 μ e V on a biological system are reported. The photocycle of the proton pump bacteriorhodopsin (BR) is known to slow down with decreasing temperature and humidity, a behaviour related to the ‘dynamic transition’. We have achieved a separation of the pure thermal activation effect involving the plasticizing action of hydration water, from effects due to the variation of the hydration level on the dynamics of purple membrane (PM) with its integral protein BR, and have correlated this with its ability to function. This demonstrates that the biological function of BR requires molecular dynamics in the ps range.