C. Vanderstruijf et al., ROTATIONAL MOTION OF CA-ATPASE MONITORED BY ELECTRON-SPIN ECHOES, Journal of magnetic resonance. Series B, 111(2), 1996, pp. 158-167
Electron spin echoes are used to study the dynamics of different aggre
gational forms of spin-labeled Ca-ATPase in the sarcoplasmic reticulum
membrane, The 2D-ESE measurements are sensitive to motions on the mic
rosecond time scale, The motional information is extracted from the va
riation of the echo decays across the CW-ESR absorption spectrum, The
motional contribution to the decays is described by assuming that the
Ca-ATPase molecule is perfectly oriented along the normal to the membr
ane surface and only undergoes rotational motion about its long axis,
The echo-amplitude decays have been evaluated in the time domain by so
lving the Bloch equations for the stochastic spin Hamiltonian on makin
g use of stochastic trajectories for the orientational behavior of the
spin-labeled protein, This approach provides a useful insight into th
e information provided by the 2D-ESE measurements and affords a direct
comparison of the results obtained with different experimental techni
ques, It is shown that the 2D-ESE technique monitors the orientational
motions of dimers or larger aggregates of Ca-ATPase molecules whose r
otational correlation times vary between 200 mu s and 1 ms for the tem
perature range between 37 and 4 degrees C. (C) 1996 Academic Press, In
c.