The dynamical transition in proteins of bacterial photosynthetic reaction centers observed by echo-detected EPR of specific spin labels

Wageningen University Laboratory of Biophysics Wageningen The Netherlands
Applied Magnetic Resonance (Impact Factor: 1.17). 03/2007; 31(1):159-166. DOI: 10.1007/BF03166253


An echo-detected electron paramagnetic resonance (ED EPR) approach was used to study molecular dynamics in photosynthetic
reaction centers (RCs) fromRhodobacter sphaeroides R26, employing the specific spin label methanethiosulfonate and 3-maliemido proxyl. ED EPR has recently been shown to be
sensitive to so-called dynamical transition in disordered media, which is characterized by the transition from a harmonic-like
librational motion of a molecule to an anharmonic one or to a stochastic wobbling motion. ED EPR line shapes studied over
a wide temperature range reveal a sharp transition occurring above 180 K. The possible relation of the found transition to
the temperature dependence of electron transfer reactions in RC is discussed.

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